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CHEMICAL ESSAYS..
CHEMICAL ESSAYS.
Richard
BY
bp. of Llandaff
WATSON, D.D. F.R.S.
AND REGIUS PROFESSOR OF DIVINITY IN
THE UNIVERSITY OF CAMBRIDGE.
VOL. III.
FOURTH EDITION.
3
LONDON.
PRINTED FOR T. EVANS,
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MDCCLXXXVII.
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SOLD BY OPDER OF THE
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Hodgson
7-5-37
3867 CONTENTS.
ESSAY
I. Of Bitumens and Charcoal. Page 1
II. Of the Quantity of Water evapo-
rated from the Surface of the Earth
in hot Weather.
III. Of Water diffolved in Air.
51
75
IV. Of Cold produced during the Eva-
poration of Water, and the Solu-
tion of Salts.
119
V. Of the Degrees of Heat in which
Water begins to part with its Air,
and in which it boils.
143
VI. Of Water in a folid State; of the
Heat of Spring Water; and of a
probable Cauſe of the Impregnation
of fuipbureous Waters.
171
VII. Of
3
CONTENT S.
ESSAY
VII. Of Derbyshire Lead Ore.
207
VIII. Of the fmelting of Lead Ore, as
practifed in Derbyshire.
251
IX. Of Silver extracted from Lead. 301
X. Of Red and White Lead.
337
:
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COLLECTION of THEOLOGICAL TRACTS,
"A By RICHARD WATSON, D. D. F. R.S.
Lord Bishop of Landaff, and Regius Profeffor of Divinity in
the University of Cambridge.
In Six large Volumes, Octavo, Price 11. 11s. 6d. fewed.
2. The Works of SAMUEL JOHNSON, L. L. D. with
his Life, by Sir John Hawkins. Eleven vols. 8vo. Price
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3. The Hiftory of the firft Ten Years of the Reign of George
the Third, King of Great Britain, &c. from his Acceffion
to the Throne, in 1760, to the Conclufion of the Third
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4. The Hiftory of the Second Ten Years of the Reign of
George the Third, King of Great Britain, &c. from the
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teenth Parliament of Great Britain, in 1780. 8vo. Price
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the Reign of George the Third, King of Great Britain, &c.
to the Conclufion of the War which was terminated by the
Independence of America, and the Peace of Paris, in 1763.
This Work is printed in the fame Size and Manner
with Rapin's Hiflory of England, and Tindal's Continua-
tion.
5. The Reports from the Committee of Secrecy, appoint-
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the First Seffion of the Fift enth Parliament of Great Britain,
to inquire into the Caufes of the War in the Carnatic, and
of the Condition of the Bitish Poffeffions in thoſe Parts
;
and also the Report from the Committee to whom the Peti.
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i
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Edward Wheler, Efqts. Counsellors for the Government
of the Prefidency of Fort William in Bengal; and the Peti-
tion of the United Company of Merchants of England trad
ing to the East Indies, were feverally referred. Alſo,
The Reports of the Select and Secret Committees
appointed by the Houfe of Commons, affembled at Weft-
minster, in the Fifth and Sixth, Seffions of the Thirteenth
Parliament of Great Britain, to inquire into the State
Nature, and Condition of the Eaft-India Company, and of
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mittees, form the most authentic Hiftory of the Eaft-India
Company's Affairs, from the Commencement of Lord
Clive's Government, to the Conclufion of the First Sefon.
of the Fifteenth Parliament in 178,
1
6. Minutes of the Evidence taken at the Bar of the Houfe
of Commons, affembled at Westminster, in the Third Seffion
of the Fifteenth Parliament of Great Britain, and of the
Proceedings of the Houfe on the hearing of Counſel on the
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lors and Members of the aid Committee, of the Settlement
of Fort St. George, on the Coast of Coromandel, in the
Eaft Indies, In One Volume Folio. Price 11. 11. 6d..
fewed.
ESSAY I
OF BITUMENS AND CHARCOAL.
THE
HE analyfes of pitcoal and of
different woods, mentioned in
the laft Effay, may ferve as inftances
of the products obtainable by diftil-
lation from bituminous and vege-
table fubftances in general. They
all of them yield water impregnated
with an acid, and often alfo with a
volatile alkaline falt, air, oils of dif-
ferent colours, weights, and conſiſt-
ences, and a black coaly refiduum.
The bitumens generally taken notice
VOL. III.
A
of
( 2 )
of by writers on Natural Hiftory
are, with reſpect to their confiftence,
either as fluid as oil, or as thick and
tenacious as tar, or quite folid. The
fluid bitumens are two, Naptha, and
Petroleum, or rock-oil. Theſe are oils
which differ from each other in co-
lour and confiftence, and fome other
properties; the naptha is pale, light,
and very inflammable; the petroleum
is yellow, brown, or blackiſh, hea-
vier and lefs inflammable than nap-
tha: its difference from naptha is
attributed to its containing a greater
quantity of acid in its compofition.
Both thefe oils are found in many
parts of the globe, either floating on
ſpring water, or dripping from the
crevices of rocks. Mineral pitch is
a bitumen which differs from petro-
leum in being thicker, heavier,
4
and
( 3 )
and more glutinous; it was formerly
found in the environs of Babylon, and
conftituted, according to Vitruvius,
when mixed with lime, the cement
which was uſed in building the walls
of that city. At prefent it is met.
with in feveral parts of Europe, and
in America, where it drips from
rocks, and is called by us Barbadoes
tar: it has a very offenfive ſmell,
and great tenacity, and is called
by the inhabitants of Auvergne, in
France, where it exudes from the
earth, and ſticks to the feet, devils
dung. The Afpbaltum, or Jews-pitch,
is a bitumen much refembling mine-
ral pitch; it is thrown up in a liquid
form from the bottom of the lake
where Sodom and Gomorrah ftood,
otherwife called the Dead Sea, or the
lake Afphaltes, from a Greek word
denoting
A 2
( 4 )
denoting a bitumen. This lake in the
time of Efdras yielded Bitumen-re-
member what I did to Sodom and Gomor-
rab, whofe land lieth in clods of pitch*.
The bitumen floating upon the fur-
face of the falt water, is condenfed by
the heat of the fun into a ſolid form,
and is gathered by the Arabs on the
fhore where it is thrown. It is faid
to be the fame fubftance which the
Egyptians uſed in embalming their
mummies, and it was called by them
mumia mineralis. This bitumen has
been found in many places of Afia
and Europe, as well as on the fhores
of the Dead Sea; all that we meet
with in the ſhops, is either an arti-
ficial compofition, or an European
afphaltum, the Eaftern ones being
feldom brought into Europe, but
uftd
* Efd. B. 2. c. 2.
Haffelquift's Voy, p. 285,
( 5 )
ufed by the natives either as pitch
for their fhips, or as an ingredient
in varnishing, or dying wool,
There is a very curious experi-
ment which illuftrates the relation
which thefe four bitumens bear to
each other. The moft tranfparent
oil of turpentine, refembling nap-
tha, may be changed into an oil re-
fembling petroleum, by mixing it
with a ſmall portion of the acid of
vitriol; with a larger proportion of
the acid the mixture becomes black
and tenacious, like Barbadoes tar;
and the proportions of the ingre-
dients may be fo adjufted, that the
mixture will acquire a folid confift-
ence, like afphaltum. This experi-
ment teaches us to conclude that
naptha, petroleum, Barbadoes tar,
and afphaltum, differ chiefly from
each
A 3
( 6 )
each other, with refpect to the quan-
tity of acid which enters into their
compoſition; and the ſubſtances pro-
cured by diftilling pitcoal, or refi-
nous vegetables may furniſh no im-
probable conjecture concerning the
origin of theſe bitumens.
Let us fuppofe then a fubterra-
neous fire to be fituated in or near
a ftratum of pitcoal, of turf, of
foffil wood, or of any other ſuch
bituminous matter; it is manifeft
that the inflammable air, and the dif-
ferent kinds of oils, which were col-
lected by diftilling fmall portions of
theſe ſubſtances, would be elevated
by the heat into the crevices of the
fuperincumbent ftrata; the light and
pale oil would be a fort of naptha,
or petroleum, the black and tena-
cious oil would be a Barbadoes tar,
and
( 7 )
and this might be fo dried by the
heat as to become an afphaltum.
The oils not being mifcible with
water, would be found floating upon
its furface, as it iffued out of the
bowels of the earth, and being very
inflammable, might conftitute burn-
ing wells, fuch as have been met
with near Wigan, at Brofely, and in
many other places: or where the oil
did not meet with water, or was too
heavy to float on it, we may conceive
that it would impregnate the porous
ftrata of feveral kinds of ftones and
earth. It has been obferved in another
place, that they formerly obtained a
fort of tar, from a ſtone at Brofely,
and the ftratum, which is called
fale in Derbyshire, is fo ftrongly im-
pregnated with oil, that it will burn
* Vol. II. p. 347.
A 4
of
( 8 )
of itſelf, when fet on fire : the work-
men in digging through the black
ftone, which is incumbent on the
fhale, fometimes meet with cavities
containing a thick black oil, which
has oozed out of the furrounding
ftone. One of the greateft foughs, or
fubterraneous paffages, which has,
perhaps ever been formed in Great
Britain, is that which is called Hell-
car fough, in Derbyshire; this fough
is driven through a ftratum of fhale,
and the workmen are much troubled
with inflammable air, which general-
ly breaks into the fough, through the
fame crannies which give paffage to
little streams of water: they ſecure
themſelves from the air, by keeping
great fans conftantly in motion; for
the inflammable air, being lighter
than common air, floats near the roof
of
(9)
of the fough, and being drawn down
from thence, and mixed with the
common air by the motion of the
fans, it is circulated in the fough
without danger. I am fenfible that
inflammable air may be produced by
various other ways, as well as by the
application of heat, to bituminous
ftrata; but as bitumens do yield in-
flammable air by diftillation, it is
probable enough, that fuch as is met
with in bituminous ftrata, may fome-
times, at leaft, be referred to the
action of a fire, fituated, perhaps, at
too great a diſtance from the furface
of the earth, to produce any other
fenfible effect.
In the Duchy of Modena in Italy,
there is a remarkable rock, which
confirms very much the notion of
oils and pitchy fubftances being fe-
parated
( 10 )
parated from bitumens by a kind of
fubterraneous diftillation. The in-
habitants of the district, by piercing
the fides of this rock, at different
diſtances from its fummit, obtain
oils of different natures, thickening
and growing heavier and deeper
coloured, as the canals through
which they flow approach to the fur-
face of the earth; at the distance of
a few feet below the furface, they
find a very thick oil, which in dig-
ging deeper becomes foft as butter,
and at ftill a greater depth, it is
found to be as folid as pitch.
Befides pitcoal and afphaltum, there
are three other folid bitumens which
deferve to be mentioned-Fet-
Amber—Ambergris. Jet fo much
refembles cannel-coal in its colour,
in its hardneſs, in its receiving a
poliſh,
( 11 )
polish, in its not foiling the fingers
when rubbed upon it, and in other
properties, that many authors con-
found the two fubftances together;
and indeed they agree in fo many
qualities that it is fomewhat difficult
to ſay in what they difagree. Jet,
however, when warmed by friction,
has the property of attracting bits
of ſtraw, feathers, and other light
bodies; but I never obferved this
property in any of the cannel-coals
which I have tried. This property,
if it may be generally relied on, as
appertaining to jet, and not to can-
nel-coal, is a very eafy characteriſtic,
by which theſe fubftances may be
diftinguifhed from each other. Jet
is faid to be found only in fmall de-
tached pieces, and that it is thereby
diftinguishable from cannel-coal,
which
( 12 )
J.
which is found in large beds. Some
think that the woody fibrous tiffue
of jet, may ferve to diftinguish it
from cannel-coal, but whoever ex-
amines large quantities of this kind
of coal, will fee many pieces which
much reſemble wood in texture.
The weight of a cubic foot of can-
nel-coal is 1273 ounces; a cubic foot
of jet is faid by one author to weigh
1238,* by another 1180 ounces.
The natural hiftory of Amber is
very obfcure.
This bitumen was
for a long time thought to be re-
ftricted to the coafts of Pruffia, on
the Baltic Sea. It was fuppofed to
owe its origin to the exudations of
certain trees on the coaſt of Sweden,
which falling into the fea, were there
hardened by the continual action of
Martin. Lewis, Newm. Chem.
the
( 13 )
the falts, and thence carried by par
ticular winds to the open coafts of
Pruffia. This opinion was fupported
by, and formed to account for, the
ants, flies, fpiders, leaves of trees,
and other terreftrial matters, which
are almost always found incloſed in
pieces of amber, and which no doubt
muſt be admitted, as proving its be-
ing originally in a fluid ftate. In
Pruffia they not only gather amber
on the fea coaft, but they frequently
find it at the depth of eight or ten
feet beneath the furface of the earth,
but at no great diſtance from the fea.
The fuperincumbent ſtrata are fand,
clay, foffil-wood, pyrites, fand again,
in which the amber is found, fome-
times in detached pieces, fometimes
in little heaps. This diftribution of
the ftrata, where amber is found, to-
0:1
gether
( 14 )
gether with their proximity to the
fea, has made it with fome degree of
probability be imagined, that this
mineral owed its fituation to the
inundation and receffion of the fea,
and that it was derived partly from
an oil arifing from the decompofition
of vegetables by fubterraneous fires,
and partly from a mineral acid.
Amber is frequently found in Italy,
where they have no foffil-wood, but
great plenty of petroleum.
The natural history of Ambergris is
as uncertain as that of amber, unless we
admit the defcription which has been
lately given of its origin, as the true
one. We are told that ambergris is
a part of the Cachalot or Spermaceti-
whale. "It is found in this animal,
in the place where the feminal veffels
are ufually fituated in other animals.
It
( 15 5)
)
It is found in a bag of three or four
feet long, in round lumps, from one
to twenty pounds weight, floating in
a fluid rather thinner than oil, and of
a yellowish colour. There are never
feen more than four at a time in one
of thefe bags; and that which weigh-
ed twenty pounds, and which was
the largest ever feen, was found
fingle. Theſe balls of ambergris are
not found in all fishes of this kind,
but chiefly in the oldeſt and ſtrong-
eft.*" This account feems probable
enough, for ambergris is a fine per-
fume, and we know that other per-
fumes, fuch as civet, mufk, and caf-
tor, are fituated in the inguinal re-
gions of the civet cat, the mufk ani-
mal and the beaver.
All vegetable, and bituminous,
and
Goldſmith's Nat. Hift. Vol. VI. p. 220.-
(16)
and indeed all animal fubftances,
leave, after their volatile principles
have been feparated by diftillation,
a black coal. Thefe coals differ fome-
what from each other, with refpect
to their proneness to catch fire, and
their ability to fupport it, but I will
content myfelf with examining the
nature of the refidue, from the dif
tillation of wood.
This refidue does not differ from
what is generally called charcoal; the
flightest attention to the manner of
obtaining this refidue, and of making
charcoal, will convince us, that no
difference ought to be expected.
When the wood is distilled, its com-
munication with the external air is
obftructed, its volatile parts are ele-
vated from it, by the heat to which
it is expofed, and the refidue is that
part
( 17 )
part of the wood which remains after
all the volatile parts are driven off.
In making charcoal they conftruct
a pile of wood upon the furface of
the ground, they cover the pile
with a coating of turf, or other fub-
ſtances, and make the coating fo
compact, that it will not admit of
air, except through fome little round
holes, which are purpoſely made in
it, and which can be ſtopped at plea-
fure. When the pile, thus conftruct-
ed, is fet on fire, part of the oil of
the wood is confumed during the
burning of the pile, the other part,
together with the air and water con-
tained in the wood, is evaporated,
and there remains, when the opera-
tion is finished, the earthy part of
the wood, called in that ftate, char-
coal. Thus the making of charcoal
VOL. II.
В
is
( 18 )
is a kind of diſtillation, for the coat-
ing which furrounds the pile of
wood, may be compared to a retort.
Henckel informs us, that 150lbs.
of oak, will produce 62 lbs. of char-
coal; but he does not inform us
whether the oak was dry or green,
whether it had its bark on or was
peeled, whether it was all heart of
oak, or partly heart, and partly fap,
whether the operation of making the
charcoal was difcontinued as foon as
the wood ceafed to fmoke, or pro-
tracted fome time longer; and yet a
difference in any one of thefe circum-
ftances, will fenfibly influence the
weight of the charcoal, procurable
from a definite weight of wood.
The woods which I converted into
charcoal were dry, and had been fel-
* For. Satur. c. iv. p. 55.
led
( 19 )
led many years; their relative weights
were taken with great exactnefs.
Weight of a cubic foot of
Water
1000 avoir, ounces.
Box
9.50
Oak
892
Afh
832
Mahogany
816
Walnut
790
Deal
61.5
Authors differ very much as to the
weights which they have affigned to
definite bulks of the fame kind of
wood. Thus, one eftimates the
weight of a cubic foot of dry box at
1030*; another at 1201 ounces:
one puts the weight of a cubic foot
of dry oak at 925; another at 800
ounces. To the more obvious
B 2
* Cotes's Hydrof. p. 73.
Tab. p. 237. Cotes.
P. 132.
fources
+ Ferguſon's
Emerfon's Mech.
(20)
&
Sources of this diverfity, in the
weights of equal bulks of the fame
kind of wood,-fuch as the wood
being green or dry, being cut from
the boll or branch of a tree,-one
may be added, which has not, I be-
lieve, been fufficiently attended to
I mean the great lofs of weight
►
i
which in certain circumstances, the
fame piece of wood fuftains, by a
fimple expoſure to the atmoſphere,
in the courſe of a few days.
From the middle of a branch of
an oak tree, which had been felled in
April, and expofed without its bark,
to the hot fummer of 1779, I. cut,
Sept. 4, a round piece, about fix inches
in diameter, and three in thickness:
Sept. 15, I cut from the heart of
this piece of oak a ſmall flip, 3
-inches in length,
I
of an inch in
thick.
( 21 )
I
I
thickneſs, and 79 grains in weight;
at the fame time, I cut a fimilar flip
from the fap of the fame piece, the
weight of which alfo was 79 grains :
theſe two pieces were put into the
drawer of my ſtudy table, and being
weighed again, Sept. 25, the heart
of oak had loft 8 grains, or near
of its weight; the fap had loft 12
grains, or above of its weight.
Now if the weights of feveral equal
bulks of thefe woods had been taken
on the 15th, and on the 25th of Sep-
tember, it is obvious (notwithſtand-
ing the contraction they might have
fuffered) that there would have been
fome difference in them, though the
woods themselves appeared equally
dry on both days.
This ſpeedy diminution of weight
which wood undergoes by expoſure
B 3
to:
( 22 )
to the air, being a matter of fome
importance in an economical view,
I will mention another experiment
which I made on the fubject. A
piece of afh cut March 17, 1780,
from the middle of a large tree,
which had been felled fix weeks be-
fore, was accurately weighed'; its
weight was 317 grains, its length 3
inches, and its breadth 2. It was
weighed again March 24, it had loft
in the courfe of 7 days 62 grains, or
near of its weight. I weighed this
I
S
fame piece of wood on the 25th of
Auguft in the fame year, but it had
not loft any thing of its weight, from
the 24th of March to the 25th of
Auguft. The two pieces of oak,
mentioned in the laft experiment,
were weighed alfo, on the 25th of
Auguft, 1780; they had neither of
them
( 23 )
them loft, in the courfe of eleven
months, quite grain; hence it ap-
pears, that the matter which is dif
perfed from wood after it is cut, is
foon evaporated: this matter proba-
bly confifts chiefly of water. The
carriage of wood, efpecially by land,
is very expenfive: if an oak or an
afh tree was cut into boards, or
fcantlings, upon the fpot where it is
felled, there would be a faving of
the carriage of one ton in fix or ſeven,
from the evaporation of the fub-
ftance of the wood; to fay nothing.
of chips and other refufe parts.
It is well known that all wood
becomes heavier than water, by hav-
ing the air extracted from the pores,
either by an air-pump, or by boiling.
it in water. The woods of which.
I have given the relative weights,
B 4
were
( 24 )
¡
were all of them rendered heavier
than water, by a long continuance
in cold water; for the heat of the
water in which they were put, never
exceeded 60 degrees. They funk in
the water after they had been foaked
in it for different lengths. of time,.
but it required above 100 days foak-
ing before the deal would fink. After
they had all lain in water for 110.
days, I took them out, and let them
dry by the gradual heat of the at-
moſphere for above a month; I then
weighed them, and found that box,
oak, and aſh, had each of them loft
of the weight they had before
JZ
they were put into the water; but
that mahogany, walnut, and deal,
이
​had loft only of their weight.
This lofs of weight is occafioned,
partly by the escape of fome portion
of
( 25 )
of air, and partly by a diffolution of
fome of the other principles of the
woods; for the water, in which they
were placed, had evidently acted
upon them, its colour and confift--
ence being both changed. Moſt
woods contain both a gummy and a
refinous part; and gums being folu-
ble, and refins not foluble in water,
we can have no difficulty in appre-
hending the reafon, why fome forts
of wood lofe a greater proportion of
their weight, by being immerfed in
water, and afterwards dried, than
others. Since the fame piece of
wood has very different weights,
when dry and when foaked with wa-
ter; the covering carts, ploughs,
and other huſbandry gear, ufually
made of aſh, with a coarfe kind of
paint which will keep out the rain,
is
( 26 )
is a practice full as ferviceable in
leffening the weight of the imple-
ment which is to be moved by the
ftrength of a man or horfe, as in
preferving the wood of which it is
made from decay.
I took fquare pieces of the woods
before mentioned, each piece being
3 inches in length, and weighing
exactly 96 grains, and expofed them,
when covered with fand, in a cru-
cible, to the action of the fame fire,
which was ftrong enough to keep
the crucible red hot, for three hours;.
they were, at the end of that time,
all of them converted into perfect
charcoals; the weights of the refpec-
tive charcoals were taken, whilft
they were ſtill warm, from the ope-
ration, and are expreffed in the fol-
lowing table:
5
Walnut
( 27 )
Walnut
Oak
Box
Afli
Deal
96 grs. gave 25 grs. of charcoal.
96
96
Mahogany 96
96
96
I
1
1
}
22
20
20
17
15
There is a good reaſon for remark-
ing, that the charcoals were weighed
whilft they were warm, for in weigh-
ing them a few days afterwards, I
found that they had all increafed in
weight in confequence of fomething
which they had attracted from the
atmoſphere; their weights then were
-walnut 28-oak 24-box 23-
mahogany 24-afh 18-deal 16-
grains.
The quantities of refidue remain-
ing from the diftillation of 96 ounces
of oak, box, and mahogany, were
refpectively 30, 26, and 27
ounces
(28)
4
ounces, which numbers are feverally
larger than thofe, expreffing the
quantities of charcoal obtainable
from 96 parts of thofe woods; this
difference may proceed from the
woods, employed in the two pro-
ceffes, being of different qualities,
or, more probably, from the heat in
which the charcoal was made, being
greater than that employed in the
diftillation; for the ftronger the fire,
the lefs is the quantity of charcoal,
which a definite weight of wood will
yield.
In making charcoal the workmen
obferve, that the pile of wood is
fenfibly diminiſhed in fize by the
operation; this proceeds from the
fhrinking of the wood. All the
kinds of wood which I charred were
diminished in all their dimenfions,
the
( 29 )
the mahogany, oak, and walnut,
were the leaft diminished, and the
box was the moft diminished; I
thought it had loft an eighth part of
its length. This diminution not only
depends upon the nature of the
wood, but it is influenced by the
ftrength and continuance of the heat,
that being moft diminished, which
has fuſtained the greateſt heat.
Though charcoal, from every fort
of wood, is incapable of being de-
compofed, by the ftrongest fires in
clofe veffels, yet it is a compound-
ed body, and may be decompofed
by being burned in the open air.
Van Helmont fays, that 62 pounds
of oak charcoal will, by burning,
yield only 1lb. of white afhes. The
other 61 pounds which are difperfed
into the air, he confiders as a vapour,
; of
( 30 )
of an elaſtic nature, which can neither
be collected in veffels, nor reduced
into a viſible form. This vapour he
called by a new name, gas.
*
Stahl is of opinion, that 10lbs. of
charcoal made from porous woods,
fuch as fir and fallow, will not, when
burned with a very flow fire, yield
above 1 lb. of afhest; this quan-
tity however, it muſt be remarked,
is above fix times the quantity affign-
ed by Van Helmont to oak, which
probably contains more afhes in a
definite weight of charcoal, than
either fir or fallow.
Geoffroy
* Hunc fpiritum, incognitum hactenus,
novo nomine gas, voco, qui nec vafis cogi nec
in corpus vifibile reduci poteft. Van Hel. Op.
omn. p. 193. Some derive gas from the Dutch
ghoaſt-ſpirit; others from the German gaſcht,
a frothy ebullition.
Stahlii Exper. Numero CCC. p. 17.
( 31 )
Geoffroy, from fomewhat lefs than
34 ounces of the charcoal, remaining
after the diſtillation of the heart of
guaiacum, got near three ounces of
white afhes, by calcining the coal in
an open fire for 12 hours. From
near 23 ounces of the coal, remain-
ing from the diftillation of the fap
of guaiacum, he got near 1 ounce
of afhes. And 29 ounces of the
coal, from the bark of guaiacum,
gave him 13 ounces of white
afhes*.
Laftly, M. Sage affures us that
100 pounds of charcoal will not,
when burned, furnish quite 2 ounces
of ashes t.
...
Theſe accounts, it muſt be ac-
know-
*Geoff. Mat. Med. or treatife on foreign
vegeta. by Thicknefs, p. 112.
† Exper. fur l' Alk. Vol. fluor. p. 27.
( 32 )
knowledged, differ very much, as
to the quantity of afhes obtainable
from a definite weight of charcoal;
and the difference, I think, is much
greater than what can wholly be at-
tributed to the different textures of
the feveral woods; a part of this di-
verſity may, probably, arife from a
difference in the manner of burning
the charcoal. When charcoal is
burned in fmall quantities, and in a
flow fire, lefs of its fubftance will be
diſperſed into the air, than when the
quantity is larger, and the ftream of
air which fupports the fire, is more
rapid. This feems not improbable;
but if the weight of the afhes re
maining from the burning of a defi-
nite weight of charcoal, be at all in-
fluenced by the degree of fire, it
feems reaſonable to fuppofe, that
what
( 33 )
what is driven off by the violence of
the fire, is of the fame earthy nature
as that which remains when the fire
is more moderate; at leaſt it may be
argued, that when charcoal is burned
with a flow fire, fome of its prin-
ciples, its oily principle for inftance,
though it, probably, alfo contains a
faline one, are more completely de-
compofed, than when it is confumed
with a violent fire, and that the de-
compoſition of theſe principles gives
an additional quantity of earth or
falt to the afhes.
If there be any truth in this notion,
we muſt not ſay, that the 61 pounds
of matter which, according to Van
Helmont, are difperfed into the air
from 62 pounds of charcoal, are
wholly of an elaſtic nature; fince
they may confift principally of an
VOL. III.
C
attenu-
1
(34
attenuated earth, which being driven
off by the current of air, requifite
for the maintenance of the fire, re-
mains for a time fufpended in the at-
moſpherical air, without being in its
own nature elaftic. I would not be
underſtood to ſay, that the whole of
what is diffipated, during the burn-
ing of the charcoal, is an attenuated.
earth, fince it is certain, that the
earth of the afhes is not inflammable,
and that charcoal contains fomething
which is inflammable; it is allowed.
alfo, that fimple earth is inodorous :
and it is well known that charcoal,
during its inflammation, difperfes
fomething into the air, which has a
ftrong ſmell; this fomething by which
charcoal is rendered inflammable,
and by which the air is infected with
a particular finell, during the burn-
ing
(35)
ing of the charcoal, is called by moſt
*. This
che nifts the phlogiston *.
C 2
phlogifton
Phlogiſton is a constituent part of me-
tallic fubftances, and it feeins, when fepa-
rated from them, to be of an elaftic nature.
I diftilled zinc with frong acid of vitriol, and
obtained a portion of fulphur, produced as
it fhould feem, by the acid's uniting itſelf
with the phlogiston of the zinc. No inflam-
mable vapour was produced, till the fulphur
began to be fublimed; then indeed, there
efcaped a vapour, compofed, I think, of the
attenuated parts of fulphur, which upon the
approach of a candle took fire. Another
portion of zinc was diftilled with weak acid
of vitriol; before the zinc felt the heat of the
fire, the inflammable air, feparable from zinc
by a weak acid of vitriol, paffed into the
receiver, and being fet on fire, burst it with
a great exploſion: another receiver was ap-
plied, and the diftillation continued to dry-
nefs, but not a particle of fulphur was pro-
duced, the phlogifton neceffary for its for-
mation having, probably, been feparated
from the zinc, by the violent action of the
S
acid,
}
( 36 )
phlogifton, whether it be an elaftic
inflammable fluid, or an unelaftic
earth of a particular kind, conftitutes,
probably, but a very fmall portion
of the weight of what is difperfed
into the air, from burning charcoal :
we all know what a ftrong fmell
may be diffuſed through a large
room, from the ignited fnuff of a
candle, or from a very fmall piece
of charcoal, which has not been
thoroughly burned; the vapours
iffuing from thefe fubftances are of
an oily faline nature, and are viſible:
the vapour of charcoal, though it is
too fubtle to be feen, may be of a
nature fomewhat fimilar, and capa-
ble
acid, and confumed at once by the inflam-
mation. May it not, from the compariſon
of thefe experiments, be conjectured, that the
phlogifton of metals is an elastic inflamma-
ble air?
( 37 )
ble of a very extenfive diffufion
through the air. An infant has been
known fuddenly to expire, from the
ſmoke of a candle blown out under
its noſe, and the vapour of charcoal
is moſt dangerous, when the charcoal
has not been thoroughly burnt.
It has been found by experiment,,
that the common atmofpherical air
is much altered in its properties, by
being made to pafs through red-hot
charcoal, into the vacuum of an air-
pump; it then extinguiſhes the flame
of a candle, and animals die in it *.
A fimilar change takes place, when
charcoal is confumed in an apart
ment, which has not a fufficient fup-
ply of fresh air; the inftances of per-
fons who have unhappily loft their
lives in ſuch air, are very common in
all
c 3
*Haukfbee's Exper. p. 287.
( 38 )
all countries, where much ufe is
made of charcoal; but efpecially in
Ruffia, where their apartments are
heated by ovens, containing red hot
charcoal. The change which the
atmoſpherical air undergoes, from
the burning of charcoal, may pro-
ceed either from the air, having loft
fome of its conftituent parts in com-
ing in contact with the burning char-
coal, or from its having gained
fomething from the charcoal, cr from
its having done both at the fame
time; juft as water, which paffes
through a lump of falt or fugar, lofes
a great
* Philof. Tranf. 1779, p. 325— Where
there is mention made of the Ruffian method
of recovering perfons who have been rendered
fenfeleſs by the vapour of the charcoal; it
confifts in carrying the perfon into the open
air, rubbing him with fnow or cold water, and
pouring water or milk down his throat.
( 39 )
a great part of the air it contains in:
its natural ftate, and gains a portion
of the falt, which becomes diffolved:
in it, and upon both accounts fuffers.
a change of its properties.
It is generally admitted, that char
coal and all other bodies, nitrous:
ones excepted, ceafe to burn, as foon
as they cease to be fupplied with
fresh air, and the air has, chiefly on
this account, been thought to com-
municate fomething to the fire, by
which the fire was maintained, and:
the air was confumed. And this:
opinion has been confirmed by ob-
ferving, that a definite quantity of
air was much diminiſhed in bulk by
bodies being burned in it. Thus,
if 10 cubic inches of air be made to
paſs through red hot charcoal, they
will be reduced to nine, and there.
C 4:
are:
( 40 )
are means of making the diminution
ftill greater.
Dr. Hooke advances another hy-
pothefis; he allows air to be neceſ-
fary to the ſupport of fire, but he
thinks that it contributes to this fup-
port, not by imparting any thing of
its own fubftance to the fire, but by
diffolving the inflammable principle
of bodies, as water diffolves falts:
according to the former hypothefis,
air is the food; according to this, it is
the receptacle or ſolvent of fire.
Dr. Priestley, to whofe inventive
genius and indefatigable induftry the
philo-
* Hooke's Micogr. p. 103. and Pofthum.
Works, p. 169. Juncker feems to have en-
tertained a fimilar notion-ingens aeris quan-
titas requiritur ad diffolvendas et recipiendas.
ignitas illas et ultimo motu attenuatas parti-.
culas, unde nifi fat aeris fit extinguitur ignis.
Junck, Conf. Chem. Vol. I. p. 157.
( 41 )
philofophic world is peculiarly in-
debted for his inquiries into the na-
ture of fictitious airs, has obferved,
that common air is diminiſhed one
fifth by the fumes of burning char-
coal; and this diminution, he thinks,
is fome how or other effected by the
air being highly charged with the
phlogiston of the charcoal; and he
obferves, which agrees very well with
Dr. Hooke's hypothefis, that when
any definite quantity of air is fully
faturated with phlogifton from char-
coal, no heat that he had ever ap-
plied was able to produce any more.
effect upon the charcoal *.
Though common air is diminiſhed
in bulk by the fumes of burning char-
coal, and of other bodies in a ſtate of
combuftion, yet a bottle or a bladder.
filled
Philof. Tranf. 1772. P. 225-230, . ;
( 42 )
filled with this diminiſhed air, weighs
lefs than when it is filled with com-
mon air *, in the proportion of 183
to 185. That 5 cubic inches of
common air fhould be reduced by
the fumes of burning charcoal to 4
cubic inches, and that thefe 4 cubic
inches of infected air fhould weigh
leſs than 4 cubic inches of common
air, cannot well be accounted for
without admitting, that a part of the
cubic inches of atmoſpherical air
has been, by fome means or other,
taken away, at the fame time that its
bulk was reduced to 4 cubic inches.
5
Being defirous of feeing, whether
the property I had obferved in char-
coal, with respect to its weighing lefs
when it was quite cold, than when
it was warm from the fire in which
*Prieft. Exp. and Ob. vol. II. p. 94°.
it
( 43 )
(43
it had been made, was a general pro-
perty appertaining to all hot and
cold charcoal, I weighed ſeveral
pieces when they were cold, and
again, when they were fo hot as to be
handled with difficulty, and found
that they all loft (they were of the
fame kind of wood) about 1 part in
12 of their weight, and that being.
left to cool in the open air, they re-
gained what they had loft in a few
days. This acquifition of weight
was made moſt rapidly at first, a
piece which weighed 240 grains
when cold, was reduced by being
heated, to 220 grains, and being left
to cool, it gained 9 grains in 4 hours,
and 15 grains in 8 hours. From the
manner in which charcoal is made,
it is probable that what remains ad-
herent to the wood, is not greatly
different
( 44 )
different from what is forced from
it by the laſt degree of heat; now
this confifts of an acid, and an oil
rendered thick and pitchy by its
union with an acid; may we not
hence fuppofe, that it is a portion of
fixed acid, which attracts the humi-
dity of the air, or perhaps the air it-
felf, when the charcoal is hot, and
becomes faturated therewith, and
that what was attracted is again dri-
ven off, when the charcoal is again
heated; and thus the charcoal be-
comes again capable of exerting its
attraction, and acquiring an increaſe
of weight? It is fome confirmation
of this hypothefis, that charcoal,
when taken out of hot fand, takes
fire upon expofure to the air, and
for much the fame reafon, probably,
that Homberg's pyrophorus takes
fire
(45)
裙
​fire in the open air *. Guaiacum
contains a ftronger acid than moſt
kinds of wood; and Geoffroy has
obferved, that "the coal of guaia-
cum being taken out of the retort,
and expofed to the air, even two or
three days after the procefs, takes
fire immediately of its own accord;
pro-
to
Homberg's Pyrophorus is known
every ſchool-boy. It is made by calcining
together for a proper time, and in proper
quantities, either alum or any falt containing
the vitriolic acid, with honey, fugar, flour, or
any animal or vegetable fubftance, capable
of being reduced to a coal. Part of the vi-
triolic acid being uncombined with the phlo-
gifton of the coal, and being in a dry con-
denfed ftate, attracts the humidity of the at-
inoſphere, and generates fuch a degree of heat
by its mixture with water, as is fufficient te
inflame the other part of the pyrophorus. Py-
rophori may be made without the vitriolic acid,
but fome acid probably enters into their com
pofition.
( 46 )
provided, that when the diftillation
is over, the neck of the retort be
carefully ſtopped, and the veffels and
furnace be left to cool of them-
felves *.
This property of increaſing in
weight by expofure to the air, be-
longs to the hot coal of pitcoal, as
well as to that of wood; I took
fome red hot cinders, and weighing
them in that ftate, left them to cool;
in 12 hours they had gained one
75th part in weight, and in 4 days
they had gained one thirtieth of
their weight. Some coak which had
been burned with a strong fire,
gained much less than the cinders.
It has been obferved in another
place, that charcoal may be decom-
pofed, by being diftilled with the
**
acid
Treatife on Foreign Veget. p. 111,
( 47 )
acid of vitriol; this acid robs the
charcoal of its inflammable principle,
and reduces it to an earth: no other
menftruum ſeems to have any action
upon it. What alteration might be
produced in charcoal, by quenching
it when red hot, in various menftru-
ums, or by boiling it in them, or by
keeping it immerfed in them, when
cold, for a long time, or by other
lefs obvious proceffes, it does not
fall within my deſign to inquire.
Animals and vegetables are foon
reduced by putrefaction to an earth;
many forts of ftones and metallic
fubftances are crumbled into duft by
the action of air and water; but char-
coal remains unchanged for ages,
whether it be expofed to the air, or
immerfed in water, or buried in the
earth. The beams of the theatre
* Vol. I. p. 175.
at
( 48 )
at Herculaneum were converted into
charcoal by the Lava, which over-
flowed that city; and during the
lapſe of above feventeen centu-
ries the charcoal has remained as
intire as if it had been formed but
yeſterday, and it will probably con-
tinue fo to the end of the world.
This incorruptibility, as it may be
called, of charcoal, has been known
in the moſt diſtant ages: for it has
been obferved, that the famous temple
of Epheſus was built upon wooden
piles which had been charred on the
outfide. The cuſtom of charring
the ends of pofts, which are to be
fixed in the earth, is very common;
and I have often wondered that the
fame cuſtom has not prevailed with
refpect to the wood ufed in mines.
and fubterraneous drains. The tim-
bers
(( 49 49
)
bers which fupport, in many places,
the roof of the foughs through
which there is a current of water,
are wafted away in a few years, that
part of them eſpecially which is ex-
pofed to the alternatives of moiſture
and dryness by the rifing and falling
of the water is foon rotted, and this
part one would think would be char-
red with great advantage.
VOL. III.
D
ESSAY
ESSAY II.
OF THE QUANTITY OF WATER EVA-
PORATED FROM THE SURFACE OF
THE EARTH IN HOT WEATHER.
THE
HERE are many operations.
conftantly carrying on by na-
tural means, which, though they
efcape the ordinary obfervation of
our fenfes, fufficiently excite our af-
toniſhment, when once difcovered.
The vast quantity of a particular
kind of air, with which the atmo-
ſphere is daily impregnated, from
the combuſtion of all forts of fuel, is
D 2
One
( 52 )
one inftance of this kind; and the
water which is raifed into the atmo-
fphere from the furface of the earth,
is another. Who would have con-
jectured, that an acre of ground,
even after having been parched by
the heat of the fun in fummer, dif-
perfed into the air above 1600 gal-
lons of water in the fpace of twelve
of the hotteft hours of the day? No
vapour is feen to afcend, and we
little fuppofe that in the hotteft part
of the day, more ufually does afcend
than in any other. The experiment
from which I draw this conclufion,
is fo eafy to be made, that every one
may fatisfy himſelf of the truth of it.
On the 2d of June, 1779, when the
fun fhone bright and hot, I put a
large drinking glaſs, with its mouth
downwards, upon a grafs-plat which
5
was
( 53 )
was mown clofe; there had been no
rain for above a month, and the
grafs was become brown; in lefs
than two minutes the infide of the
glafs was clouded with a vapour,
and in half an hour drops of water
began to trickle down its infide, in
various places. This experiment was
repeated ſeveral times with the fame
fuccefs.
That I might accurately estimate
the quantity, thus raifed, in any cer-
tain portion of time, I measured the
area of the mouth of the glafs, and
found it to be 20 fquare inches :
there are 1296 fquare inches in a
fquare yard, and 4840 fquare yards
in a ſtatute acre; hence, if we can
find the means of meafuring the
quantity of vapour raifed from 20
fquare inches of earth, fuppofe in
D 3
one
( 54 )
one quarter of an hour, it will be an
eafy matter to calculate the quantity
which would be raifed with the fame
degree of heat, from an acre in 12
hours. The method I took to mea-
fure the quantity of vapour, was not
perhaps the most accurate which
might be thought of, but it was fim-
ple and eaſy to be practifed: when
the glaſs had ſtood on the graſs-plat
one quarter of an hour, and had
collected a quantity of vapour, I
wiped its infide with a piece of muf-
lin, the weight of which had been
previouſly taken; as foon as the
glafs was wiped dry, the muflin was
weighed again, its increaſe of weight
thewed the quantity of vapour which
had been collected. The medium
increaſe of weight, from feveral ex-
periments made on the fame day,
between
1
( 55 )
between 12 and 3 o'clock, was 6
grains collected in one quarter of an
hour, from 20 fquare inches. of
earth. If the reader takes the trou-
ble to make the calculation, he will,
find that above 1600 gallons, reck-
oning 8 pints to a gallon, and efti-
mating the weight of a pint of wa-
ter at one pound avoirdupois, or
7000 grains troy weight, would be
raifed, at the rate here mentioned,
from an acre of ground in 24 hours.
It may eafily be conceived, that
the quantity thus elevated will be
greater when the ground has been
well foaked with rain, provided the
heat be the fame; I did not happen
to mark the heat of the ground when
I made the fore-mentioned experi-
ments; the two following are more
circumftantial: the ground had been
WEE-
( 56 )
wetted the day before I made them
by a thunder fhower, the heat of the
earth, at the time of making them,
eftimated by a thermometer laid on
the grafs, was 96 degrees; one ex-
periment gave 1973 gallons from
an acre in 12 hours, the other gave
1905. Another experiment made,
when there had been no rain for a
week, and the heat of the earth was
110 degrees, gave after the rate of
2800 gallons from an acre in 12
hours; the earth was hotter than the
air, as it was expofed to the reflec-
tion of the fun's rays from a brick.
wall.
The heat in Bengal in the fummer
months is variable, in the ſhade from
98 to 120 degrees *, and in the fun
it probably does not fall fhort of
140
* Philof. Tranf. 1767, page 218, and for
the year 1775, p. 202.
( 57 )
140 degrees; hence, after the earth
has been well drenched by the over-
flowing of the Ganges, immenſe
quantities of vapours must be daily
raiſed, to the amount, perhaps, of
five or fix thoufand gallons from an
acre, in twenty-four hours. The
rainy feafon in Bengal lafts from the
beginning of June to the middle of
October; all this interval is confidered
as an unhealthy time, but especially
the latter part of it, for then the
earth begins to grow dry, the flime
left upon its furface, confifting of
decayed vegetables and other putref-
cent bodies, begins to corrupt; and
the fun, by its violent and continued
action, raiſes up into the air not a
pure water, but water impregnated
with putrid particles of all kinds.
Whether a merely moift fituation
be
( 58 )
be unwholeſome, may be much
queftioned; but that moiſture arifing
from earth or water in a ſtate of pu-
trefaction is fo, cannot well be
doubted. The overflowing of the
Nile puts a ſtop to the plague in
Egypt, infomuch, probably, as it puts
a ſtop to the putrefaction of the ca-
nals of Grand Cairo and other places.
Agues and putrid fevers are much
more frequent in the fens of Cem-
bridgeshire and Lincolnshire in very
dry, than in wet years; the Irish, who
annually come to reap the harveft in
the fens of Cambridgeshire, have
been ſo ſenſible of the difference,
that for the three or four years lat
paſt, which have been very dry, they
have entered upon their task with
great reluctance, and apprehenfion of
what they call the Fen-fbake. The
States
( 59 )
States of Holland, in the year 1748,
laid the country around Breda under
water, and ordered the water to be
kept up till the winter, in order to
ftop a fickneſs which had ariſen from
the moist and putrid exhalations of
half-drained grounds *. The Arabs
are faid to take a horrid kind of
vengeance when they think them-
felves injured by the Turks at Baffora;
they contrive to overflow the adjoin-
ing country a peftilential fever be-
gins to fhew itfelf as the land begins
to grow dry by the evaporation of
the water, and it rages with fuch
violence as to carry off many thou-
fands of the inhabitants of that city .
The nature of the foil muſt have
a great influence on the health of the
people
*Sir J. Pringle's Dif. of the Army, p. 63.
+ Philof. Tranf. 1778, p. 215.
( 60 )
people who inhabit it, fo far as that
is dependent on the moisture or dry-
neſs of the air. There is, probably,
as much water raifed into the air,
in a hot day, from an acre of ground
in the fens of Cambridgeshire, as is
raiſed in two or three days from an
equal furface in the fandy parts of
Norfolk and Sufolk. Not but the
moft fandy country may have a very
moiſt atmoſphere, when water hap-
pens to be found near the ſurface;
for the heat of the fun will penetrate
through the fand, and raife the water
in vapour, which will find an eaſier
paffage through the fand than it
would do through a lefs open foil.
Thus the foil in fome parts of Dutch
Brabant is a barren fand, but water
is every where to be met with at the
depth of two or three feet, and in
propor-
( 61 )
proportion to its diftance from the
furface the inhabitants are free from
difeafes *
Vegetation must be greatly influ-
enced by the quantity of water which
is raiſed from the earth; fome foils
retain humidity much longer than
others, and one great ufe of marles
and other manures, is, to render the
foil on which they are put lefs liable
to be deprived of its moiſture by
the heat of fummer. The water, in af-
cending from the bofom of the earth,
moiſtens the roots, and in being dif-
folved in the air, it affords nutriment
to the branches of vegetables; but
as vegetation may be injured either
by a defect, or an excefs of moiſture,
and as different plants require dif-
ferent quantities of it, for attaining
*Difeaf. of the Army, p. 62.
their
( 62 )
their utmoſt perfection, it merits the
attentive obfervation of the farmer
to fuit his plants and his manures to
the nature of the foil. There are many
fandy and limeftone foils, which are
covered almoſt with flints or lime-
ftone pebbles; the crop of corn
would, probably, be lefs, if thefe
ftones were removed: for they are
ferviceable, not only in fheltering
the firft germs of the plant from
cutting winds, but they impede the
eſcape of moisture from the earth;
the afcending vapour ftrikes upon
that ſurface of the ftone which is
contiguous to the earth, and is there-
by condenſed, and thus its further af-
cent is for a time, at leaſt, prevented.
Upon the fame grafs-plat, and
contiguous to the glaſs uſed in the
experiments, I placed a filver cup,
with
( 63 )
with its mouth downwards, of a
fhape fimilar to that of the glaſs, and
nearly of the fame dimenfions; but
I could never obferve that its infide
had collected the leaft particle of
vapour, though I frequently let it
ftand on the graſs for half an hour,
or more.
By means of a little bees wax, I
faftened an half crown very near, but
not quite contiguous, to the fide of
the glafs, and fetting the glafs, with
its mouth downwards, on the grafs,
it prefently became covered with va-
pour, except that part of it which
was near to the half crown. Not
only the half crown itſelf was free
from vapour, but it had hindered
any from fettling on the glafs which
was near it, for there was a little
ring of glafs furrounding the half
crown
( 64 )
crown to the diſtance of of an inch
which was quite dry, as well as that
part of the glafs which was imme-
diately under the half crown; it
feemed as if the filver had repelled
the water to that diſtance. A large
red wafer had the fame effect as the
half crown; it was neither wetted
itſelf, nor was the ring of glaſs
contiguous to it wetted. A circle of
white paper produced the fame effect,
fo did ſeveral other fubftances, which
it would be tedious to enumerate.
Theſe phenomena, refpecting the
different difpofitions of different bo-
dies to attract the rifing vapour, are
fimilar to what others have taken
notice of concerning the falling of
dew, and are, probably, to be ex-
plained upon the fame principles,
whatever they may be. Mufchen-
broek
( 65 )
broek placed on the leaden terrace of
the Obfervatory at Utrecht, veſſels
of glaſs, china, varniſhed wood, po-
liſhed brass, and pewter; he found
that in the courſe of a night the glaſs,
china, and varniſhed wood, had col-
lected a great abundance of dew,
but that not a drop had fallen on any
of the poliſhed metals *. M. du
Fay expofed to the air, when the
dew was falling, two large funnels,
one made of glafs, the other of po-
liſhed pewter; the necks of the fun-
nels being inferted into veffels pro-
per to retain any moisture which
might be collected by them; he
fometimes found in the morning that
the veffel under the glafs funnel con-
tained an ounce or more of water,
VOL. IIJ.
E
but
* Introd. ad Philof. Nat. Tom. I. p. 992.
( 66 )
but he never obferved fo much as a
drop in the other*.
A great part of the water which
is raiſed into the air from the per-
fpiration of the earth during a hot
day, defcends down again upon its
furface in the courſe of the night;
and this is the reafon that the dews
are the greateſt in the hotteft wea-
ther, and in the hotteſt climates.
The earth retains the heat it receives
in confequence of the fun's action
longer than the air does; water,
moreover, is evaporable in all de-
grees of heat; hence water may con-
tinue to riſe from the earth, when
the air, being cooled by the abſence
of the fun, is no longer able to fuftain
what is thus raiſed, or to retain what
• Hift. de l'Acad. des Scien. 1749.
it
( 67 )
it had taken up during the day time,
and a dew from thefe different caufes
may, under certain circumftances,
be found both to rife and fall during
the whole night.
Egypt, at one feafon of the year,
is fo parched up by the heat, that
the ſurface of the ground becomes
quite rugged with fiffures; at this
time the dew, proceeding from the
vapour exhaled from the earth, is
very plentiful, and by its plenty pre-
vents the total deftruction of the
country. "This dew is particularly
ferviceable to the trees, which would
otherwife never be able to refift the
heat; but with this affiftance they
thrive very well, bloffom and ripen
their fruit. Therefore, the upper
parts of the Egyptian trees, at one
time of the year, do the office of
E 2
roots,
(68
( 68 )
roots, attracting nourishment by
their abſorbent veffels, the leaves,
from the moiſt air.*"
The quantity of water which was
condenfed on the infide of the glafs,
I found to be accurately proportion-
able to the time during which it
ſtood on the grafs; for in one ex-
periment 6 grains were collected in
10 minutes, and in another 15 grains.
were collected in 25 minutes; now
the proportion of 6 to 10 is the fame
as that of 15 to 25.
•
In order to fee whether the copious
vapour collected by the glafs was
owing to the natural perſpiration of
the grafs, or to a kind of mechanical
diftillation from the body of the
earth, I put the glafs upon a foot-
path which was dry, and had no
grafs
Haffelquift's Voy. p. 455.
( 69 )
grafs growing upon it, the vapour
rofe from the footpath as well as
from the grafs, but not fo abun-
dantly.
From what has been advanced,
it may, probably, be justly inferred,
that the air contiguous to, or not
far removed from, the furface of the
earth, whether that furface be plain
or mountainous, barren, or covered
with vegetables, will be much more.
loaded with the vapour which arifes
conftantly from the earth, than that
which is at the distance of even a
few yards from the furface. This
point may be illuftrated by the fol-
lowing hypothefis Suppofe the
earth to be a globe of rock falt, and
to be covered with water to the
height of a mile; imagine the wa-
ter to be divided into four fpherical-
E 3
fhells,
( 70 )
8.70
thells, each
of a mile in thickness.
Now the first fhell, which is fup-
pofed to be contiguous to the fur-
face of the falt, would foon faturate
itſelf with the falt, and becoming
thereby heavier than the water at a
greater diſtance, it would not, by
the ordinary motion of the winds
and tides, foon mix itfelf with the
whole mafs of water; but it would
contain far more falt in folution than
the ſecond ſhell, and the ſecond
would contain more than the third,
and the third more than the fourth.
Let us further fuppofe the falt con-
tained in the whole of the water to
be precipitated, and the precipita-
tion to begin from the fhell fartheſt
emoved from the furface of the
earth; it is evident, that the quan-
tity of the precipitate will increaſe,
not
( 71 )
not fimply with the increaſe of ſpace
through which it has defcended, but
in a much higher proportion, inaf-
much as the laft fhell through which
it defcends may be fuppofed to con-
tain three or four times as much falt
as the uppermoft. In like manner,
it ſeems reaſonable to fuppofe that
the air which is near the furface of
the earth will be much more charg-
ed with water, which it diffolves as
water diffolves falt, than that which
is fituated at the diftance of even a
few yards from the ſurface.
Dr. Heberden was the first perfon
who took notice that a much larger
quantity of rain falls into a rain-
gage ſituated near the furface of the
earth, than into one of the fame di-
menſions ſituated a few yards above
E 4
it:
( 72 )
}
it; and he thinks that this differ-
ence is to be explained from fome
unknown property of electricity.
The fact is placed beyond contro-
verfy, by experiments which have
been made at various places; at
Liverpool in particular it has been
obferved, that "a veſſel ſtanding on
the ground in a ſpacious garden, re-
ceived double the quantity of rain
which fell into another veffel of
equal dimenfions placed near the
fame fpot, but eighteen yards high-
ert." I am far from thinking that
the foregoing obfervations relative
to the quantities of water contained
in equal bulks of air at different
heights
*Phil. Tranf. 1769, p. 361.
See an ingenious effay on the fubject, by
Dr. Percival, who has explained the pheno-
menon from the known principles of electri
city. Effays by Dr. Percival, p. 112.
( 73 )
heights from the furface of the earth,
contain a fatisfactory explanation of
this phenomenon; yet it may be re-
marked, that rain-gages placed at
equal diftances from the furface of
the earth, collected nearly equal
quantities of rain, though one of
them was fituated on a plain, and the
other on a mountain 450 yards in
height above the plain*: this obſer-
vation is fome confirmation of the
hypothefis which has been mention-
ed, as on that fuppofition it follows,
that the air at the fame diſtance from
the furface of the earth, is equally
impregnated with water, other cir-
cumſtances being the fame, and
therefore equal quantities of rain
ought to be collected by veffels
placed at equal diſtances from the fur-
* Philoſ, Tranſ. 1772, P. 294•
face
(74)
face of the earth; though according
to the fame fuppofition, a much
larger quantity ought to be collected
by a veffel placed on the furface,
than by one placed a few yards above
it. Thus this hypothefis, admitting
its truth (which future experiments
will perhaps eſtabliſh), ſeems as if it
was fufficient for explaining the phe-
nomenon; I would be underſtood
however to mention it with much
diffidence, and was I as much ſkilled
in electricity, as the very worthy and
ingenious perfon, who firft noticed
the fact, is in every branch of natu-
ral philofophy, I might probably
have ſeen reaſon not to mention it at
all.
요
​ESSAY
ESSAY III.
OF WATER DISSOLVED IN AIR.
W
E have feen, in the preced-
ing Effay, that large quan-
tities of water are raifed from the
earth in the hotteſt weather: the wa-
ter, which is thus elevated, is no
more viſible in the air, than a piece
of fugar is vifible in the water where-
in it happens to be diffolved, nor is
the tranſparency of the air injured
by the water it has received from the
earth,
( 76 )
earth, and therefore we conclude,
that the water is not merely mixed
with the air, but really diffolved in
it; a perfect tranfparency of the
fluid, in which any body is diffolved,
being efteemed the moft unequivo-
cal mark of its folution.
The cauſe of the afcent, fufpen-
fion, and deſcent of vapours, is not
yet fully determined; many think
that electricity is the principal agent
in producing theſe phenomena*;
whilst others are of opinion, that wa-
ter is raiſed and fufpended in the air,
much after the fame manner in which
falts are raiſed and fufpended in wa-
ter; and it must be owned that this
opinion
* P.
Philof. Tranſ. 1755, p. 124.—Electri-
citas vapores in aërem extollit, in aëre fuf-
pendit, et ex aëre in tellurem depluit. Prof.
Bavers Exp. de Elec. Theo. p. 106.
( 77 )
opinion (which future experience
may ſhew not to be wholly incon-
fiftent with the other) has a great
appearance of probability.
Salts, in general, are more ſpeedi-
ly diffolved in warm water than in
cold; and water, in like manner, is
more ſpeedily diffolved in warm air
than in cold. We have a ſenſible
proof of this in the exhalation of
dew, it being much fooner dried up
in places expofed to the direct rays
of the fun, than in the fhade, becauſe
the air in the fhade being fome de-
grees colder than that in the fun, is
not able to diffolve the fame quanti-
of water in the fame time.
ty
When water is faturated with any
kind of falt in a definite degree of
heat, then will it retain the falt as
long as it retains its heat; but if the
6
heat
( 78 )
heat be leffened, the tranſparency of
the ſolution will be deſtroyed, a part
of the falt will become vifible, and
fall to the bottom, in confequence of
its fuperior weight; what falls to the
bottom will be re-diffolved, as foon
as the water regains its heat. It is
obvious that the quantity of the
falt which is precipitated from the
cooling of the water, will depend
partly on the degree of heat in which
the folution is faturated, and partly
on the degree of cold to which the
folution is reduced. Thus water of
80 degrees when faturated with falt,
contains more falt than it would do
if it had only 70 degrees of heat, and
in being cooled to 50 degrees, the
precipitation of falt will be greater
in the firſt inſtance, than in the fe-
cond; though it might probably be
the
(
79 )
the fame, if the folution of 80 de-
grees was cooled only to 60, and
that of 70 to 50. Something very
analogous to all this may be obferv-
ed with reſpect to the folution of
water in air. In mifty weather we
frequently fee the mist of the morn-
ing intirely vanishing towards the
middle of the day, and coming on
again towards the evening; the rea-
fon of which feems to be, that the
air being warmed by the approach
of the fun to the meridian, is able
to diffolve the morning mift, but as
the air grows colder again towards
the evening, the water which had
been perfectly diffolved by the mid-
day heat begins to be precipitated,
the tranſparency of the air is deftroy-
ed, and an evening mift is formed.
This phenomenon has been ob-
ferved
( 80 )
ferved to prevail, in the coldeſt at-
moſphere that has ever yet been
taken notice of, on the furface of
the globe; for in January 1735,
when the cold in Siberia was equal to
157 degrees below the freezing point
in Fahrenheit's thermometer, the low-
er region of the air was obfcured by
a perpetual cloud, which was very
thick in the morning, thinner to-
wards noon, and thicker again at
night*.
Mifts and dew will, generally
fpeaking, be the greateſt when the
difference between the heat of the
air in the day time, and at night,
is the greateft, becaufe the hotter the
day, the greater is the quantity of
water which is diffolved; and the
colder the night, the greater will be
the
Novi Commen. Petrop. Tom. VI. p. 429-
( 81 )
the quantity which is precipitated.
It often happens that there is no mist
obfervable towards the clofe of the
day; this may be occafioned, either
by there being little difference in
the heat of the air at noon, and at
night; or, though that difference be
confiderable, yet the air may chance
not to be faturated with water, and
in that cafe it may, even in the night,
be warm enough to retain all the
water it had diffolved in the day
time. In cold weather the breath
of animals becomes vifible, becauſe
the air is not warm enough to dif-
folve the moiſture which is exhaled
from the lungs *
VOL. III
F
It
* The breath is visible if the temperature
of the air be colder than 61 degrees. Caval.
on Air, p. 400. The degree of cold in which
it is visible, depends partly on the humidity,
or diynefs of the air.
(82
( 82 )
It is not unufual for a river in
winter time, to be much warmer than
the air, hence, the vapour which rifes
from the river is condenſed, the air
not being able to diffolve it, and a
cloud or miſt of finall elevation, is
ſeen to accompany the river in its
courfe; this appearance ceaſes, as
foon as the river is frozen, becauſe
the ice, though it be ſubject to eva-
poration, yet it does not yield fo
much vapour as water does *.
A cubic inch of rock falt, nitre,
or any other kind of falt, is much
longer in being diffolved, when it is
in a compact ſtate, than when it is
reduced into a fine powder, becauſe..
the falt, when in the form of a pow-
der,
* Angara fluvius nocte glacie confiftit, quo
facto nebula illa perpetua, huc ufque ex fluvic
hoc evecta, ceffavit.
Vol. VI. p. 436.
Novi Comm. Petrop.
}
( 83 )
der, has a much larger furface ex-
poſed to the action of the water,
than if it was in one folid lump. In
like manner, the air will diffolve any
definite quantity of water fooner,
when the ſurface of the water is in-
creaſed by its being in the form of a
vapour, than it would do if the wa-
ter was either in the form of ice, or
in its ordinary fluid ftate. The ſmoke
of a chimney confifts principally of
water, in the ſtate of vapour, and it
is really aſtoniſhing, to fee how
quickly, in particular ſtates of the
atmoſphere, it is diffolved in the air.
It has been remarked, that the
fmoke of mount Vesuvius is much
more ftrong and vifible in rainy,
than in fair weather; if this phe-
F 2
nomenon.
*Lett. fur la Mineral. par M. Ferber,
P. 188.
1
( 84 )
nomenon does not proceed from the
greater quantity of water, which is
raiſed from the mountain in wet,
than in dry weather; it may be ac-
counted for, from the greater facility
with which, aqueous vapours are dif
folved in a dry ferene air, than in
one which is fo faturated with water,
that it can diffolve no more; which
is the cafe, in general, of air, which
parts with its water, in the form of
rain or miſt.
In riding upon wet fand in a hot
day, a kind of tremulous motion in
the air, to the height of a foot or
more above the fand, may be ob-
ferved; this appearance may proceed
from hence, that the water in rifing
from the fand, is not immediately
diffolved in the air. A fimilar appear-
ance may often be obferved on land,
efpe-
( 85 )
eſpecially in corn fields towards au-
tumn; the water which is exhaled
from the ſtanding corn, not mixing
itſelf at once, fo effectually with the
air, as to conftitute with it an appa-
rently homogeneous fluid. Some-
thing of the fame kind happens,
when either faline folutions, wines,.
or vinous fpirits of any kind, are
poured into a glaſs of water, the
compound fluid muſt be agitated,
or the mixture will not at firft be
uniform.
The quantity of water contained
in the air, even in the drieft weather,
is very confiderable. We may be
faid to walk in an ocean; the water
indeed of this ocean does not, ordi-
narily, become the object of our
fenfes, we cannot fee it, nor, whilft
it continues diffolved in the air, do
F. 3.
we
( 86 )
we feel that it wets us, but it is ftill
water, though it be neither tangible
nor viſible; juſt as fugar, when dif-
folved in water, is ftill fugar, though
we can neither fee it nor feel it.
Some philofophers have doubted,
whether the weight of the air may
not chiefly be attributed to the wa-
ter which is conftantly fufpended in
it*. But whether this conjecture be
admitted or not, the power which the
air has of keeping a great quantity of
water diffolved in it, may very
properly be applied to the illuftra-
tion of that text, in which it is ſaid,
God divided the waters which were
under the firmament, from the waters
which were above the firmament,
without having recourfe with Epif
Boerh. Chem. Vol. I. p. 461,
† Gen. i. 7.
copius
( 87 )
opius, to the very unphilofophical
fuppofition of the blue fky being
a ſolid ſubſtance compofed of con-
gealed water *. Some are puzzled
to find water enough to form an
univerfal deluge; to affift their en-
deavours it may be remarked, that
was it all precipitated which is dif
folved in the air, it might probably
be fufficient to cover the furface of
the whole earth, to the depth of
above thirty feet.
The air not only diffolves water,
but various other vapours, which con-
F. 4.
•
fift
*Extima five fuprema hujus aëris regio
attingit fornicem illum cæruleum, in quo
poftea die quarta ftellæ fixæ collocate fue-
runt; qui fornix cæruleus mihi effe videtur
aquarum in altum elevatarum, et cryftalli: in-
morem feu condenfatarum, feu conglaciata-
rum, cæruleoque colore radiantium, compa-
ges. Epif. Inf. Theol. Lib. iv. c. 3,
( 88 )
fift partly of water, and partly of vola-
tile falts and oils. All vegetables,
whether aromatic or not, are found
to perfpire very greatly, and the mat-
ter which they perfpire, could it be
condenfed, would, probably, be fo
far different from pure water, as to
have both a tafte and fmell. The
matter perfpired by animals, without
fweating, confifts principally of wa-
ter, but the water is ftrongly impreg-
nated with odorous particles. It has
been faid of Baron Haller, that he
could fmell the perfpiration of old
people, at the diſtance of ten yards;
this is by no means incredible, for the
human body is conftantly enveloped
in an inviſible cloud, arifing from the
great quantity of matter which is
infenfibly perfpired. Sanctorius efti-
mates the fenfible excretions of a
perfon
( 89 )
perfon who eats and drinks 8 lbs of
food in 24 hours, at 3 lbs, and the
infenfible perfpiration at 5 lbs; but if
we ſuppoſe the infenfible perfpira-
tion in this climate (which is colder
than that of Venice, where he made
his experiments) to amount only to
one half of our food, we cannot but
conclude, that it muft form a great
cloud around us; for 4 lbs of matter
converted into a vapour as heavy as
air, would occupy a great ſpace,
amounting to above 50 cubic feet.
The heat of the human body is ge-
nerally between 90 and 100 degrees;
this degree of heat is fufficient to
raife from it, by a kind of diftilla-
tion, a copious vapour, which would
become visible, if the heat was in-
creafed I remember having been
greatly heated and fatigued in af
cending
( 90 )
cending the ladders from the bottom
of the copper mine at Eton; when
I got to the top I obferved, by the
light of a candle, a thick vapour
reeking from the body, and visible
around it, to the diſtance of a foot
or more.
The difpofition of the air for dif
folving either pure water, or the
matter perfpired by vegetables, or
animals, is very various, depending
chiefly on its denfity, beat, and dry-
nefs. The power which dogs have
of fcenting the animal they are in
purſuit of, muſt be much affected
by this difpofition of the air; for
the air through which the animal
has paffed, is impregnated with the
matter perfpired from its body; and
this matter may in one ſtate of the
air be fo fpeedily diffolved, and fo
much
1
( 91 )
much as it were diluted with air, as
to make either no 'impreffion, or a
very flight one, on the olfactory
nerves of the dog; whilft in another,
it may make a very fenfible one.
And if we fuppofe the perfpirable
matter not to confift chiefly of wa-
ter*, but of fuch particles as are
thrown off by perfumes, without
their lofing fenfibly of their weight,
ftill it will be true, that the ſtate of
the air muſt have a great influence
in
*If the whole body of a naked man, ex-
cept his mouth and noftrils, was ſhut up in a
glaſs caſe, ſo that no air could enter, the mat-
ter of the infenfible perfpiration would, pro-
bably, be condenfed, and ftand as dew on the
infide of the glaſs; and I apprehend it would
not differ much from the matter of the fenfible
perfpiration, or fweat. But if any one be
difpofed to confider the infenfible perſpiration,
as an uncondenſable fluid, or a kind of air
fimilar
( 92 )
in rendering them fenfible; fince it
has been found, that on the tops of
very high mountains, where the ſtate
of the air is very different from
what it is in the valleys below, the
moſt odorous bodies lofe either in-
tirely, or in a great degree, their
powers of exciting a ſmell.-The
exiſtence of water in air is made ap-
parent various ways.
If a bottle of wine be fetched out
of a cool cellar, in the hotteſt and
driest day in fummer, its furface
will preſently be covered with a thick
vapour, which, when tafted, appears
to
fimilar to that which arifes from vegetable
Auids, in a fate of fermentation (the heat of
fermenting wort being much the fame as that
of an animal body), ftill its mixture with the
atmoſpherical air muft depend very much on
the weight, humidity, and other properties
of that air.
( 93 )
93)
to be pure water. This watery va❀
pour cannot proceed from any exu-
dation of the wine, through the
pores of the bottle, for glafs is im-
pervious to water, and the bottle
remains full, and when wiped dry, it
is found to weigh as much as when
taken out of the cellar. The
fame appearance is obfervable on
the outfide of a filver, or other vef-
fel in which iced water is put in
ſummer time; and it is certain, that
the water which is condenſed on the
furface of the veffel, does not pro-
ceed merely from the moisture ex-
haled by the breathing of the people.
in the room, where this appearance
is most generally noticed, becauſe
the fame effect will take place, if
the veffel be put in the open air.
Water which is cooled by the folu-
tion
(( 94
94 )
tion of any falt, or even fpring wa-
ter, which happens to be a few de-
grees colder than the air, produces
a fimilar condenfation of vapour on
the outſide of the veffel in which it
is contained. Thefe and other ap-
pearances of the fame kind, are to
be explained on the fame principle.
Warm air is able to retain more wa-
ter in folution than cold air can;
when therefore warm air becomes
contiguous to the outward furface
of a veffel, containing cold liquor,
it is preſently cooled to a certain de-
gree, and in being cooled, it is forc-
ed to part with fome of the water
which it had diffolved, and this wa-
ter, ceafing to be fufpended by the
air, attaches itſelf to the ſurface of
the cold veffel.
The more ancient philofophers,
no
( 95 )
not fufpecting that water might be
diffolved in air, were of opinion that
the moisture which they obſerved
adhering to the outfides of veffels,
which had been cooled by having
fnow put into them, proceeded from
a tranfmutation of air into water*.
But there feems to be no more rea-
fon for this fuppofition, than there
would be for faying, that water was
changed into faltpetre, from obferv-
ing that water which had diffolved
as much faltpetre as it could, in a
certain
*Naturæ myftas arcano modo, fed facili,
aërem in aquam mediis caloribus cogere docebit
abjecta hæc nix, fi vitro conicæ figuræ, intra
tripodem, apice deorfum vergente fufpenfo,
indatur nivis vel glaciei fruftum. Quippe fub-
jecto vafculo excipiuntur, exteriore vitri frigi
ditate collectæ, et laterum declivitate manantes
aquæ gutte. Bartholinus de Figura Nivis, p. 3.
See alfo Boyle's Worfts, Vol. II. p. 297.
( 96 )
certain degree of heat, depofited a
part of it, when that degree of heat
was leffened.
Another method of proving the
existence of water in the cleareſt air,
is, to obferve the increaſe of weight,
which certain bodies acquire by ex.
poſure to the open air. I put upon
a plate 8 ounces of falt of tartar,
which had been well dried on a hot
iron; the day was without a cloud,
and the barometer ftood at 30 inches;
in the ſpace of three hours, from
II to 20'clock in the afternoon, the
falt had increafed in weight two
ounces; in the courfe of a few days
its weight was increaſed to twenty
ounces, it was then quite fluid, and
being diſtilled it yielded a pure wa-
ter equal in weight nearly to the
increaſe it had acquired from the air,
3
and
(.97 )
and therefore it is rightly inferred,
that water was the fubftance which
it had attracted from the air.
Strong acid of vitriol is another
body which very powerfully attracts.
humidity from the air. An ounce
of this acid has been obſerved to
gain, in 12 months, above fix times
its own weight. The power of the
acid to attract water from the air,
depends upon its ftrength, for it
may be fo far diluted, that inſtead
of attracting any more water from
the air, it will, by evaporation, loſe a
part of that which it had acquired;
when it is in this ftate, its weight
varies with the drynefs or moiftneſs
of the atmosphere, and it becomes,
when accurately balanced in a good
pair of fcales, no bad kind of an hy-
VOL. III.
G
grometer.
Newm. Chem. by Lewis, p. 161.
(98
( 98 )
grometer. The time in which any
definite quantity of acid acquires its
greateſt weight from the air, depends
partly upon the quantity of water
which is diffolved in the air, and
partly upon the furface of the acid
which is expofed to the air, it hav-
ing been aſcertained by experiment,
that the quantity attracted from the
air, in a definite portion of time, is
greater as the furface is greater.
Hence, instead of a twelve months
expoſure to the air being requifite
to make one ounce of acid of vitriol
acquire fix ounces of water, it might
poffibly acquire that weight in a few
minutes, if its furface was enlarged
in a due proportion.
Onions and other bulbous roots,
when hung up in a room ſheltered
from rain and dew, are obſerved to
germi-
(( 99
99 ).
germinate, and to acquire a great
increaſe of bulk, and it might thence.
have been fufpected, that they at-
tracted much water from the air,
and were increaſed in weight. But
though they may increaſe in bulk,
they are found to decreafe in weight;
the root itſelf, in becoming rotten,
fupplies nutriment to the germinat-
ing plant; and if it imbibes any
thing from the air, it lofes that and
more by perſpiration. An onion
on the 26th of January, when
it had fcarce begun to fhew any
figns of vegetation, weighed 296
grains; on the reth of the following
May, after having put forth feveral
ftems in the open air, it weighed only
145 grains *.
The increaſe of weight which the
G 2
human
Novi Com. Petrop. Tom. II. p. 2
P. 225.
( 100 )
human body, in many cafes, experi-
ences from the water which the pores.
of the body fuck in from the air,
is another very fenfible proof of the
great quantity of water which is
conftantly diffolved in the air.
Keil has proved, that a young
man weakened from want of nou-
riſhment, but in other refpects
healthy, added eighteen ounces to
his weight, in the ſpace of one night,
and this by the abforption through
his pores. Another perfon has been
feen to gain 40lbs. weight, in the
ſame manner, in the ſpace of a day.
M. de Haen is of opinion, that
dropfical patients abſorb more than
100lbs. weight every day. It is
fuppofed, that in general, the body
abforbs more than 1lb, every day
by
( ΙΟΙ
by the pores." The ſkin of a
middle-fized man is equal to about
15 fquare feet, and if we fuppofe the
fkin of a dropfical perfon to be 20
fquare feet, then will each fquare
foot imbibe 5lbs. or pints of water
in one day.
In addition to thefe inftances I
will fubjoin the following account,
which was given me by a perfon of
credit and judgment. A lad at New-
market, a few years ago, having
been almoft ftarved, in order that he
might be reduced to a proper weight
for riding a match, was weighed at
9 o'clock in the morning, and again
at 10, and he was found to have
gained near 30 ounces in weight in
the courſe of an hour, though he
had
G 3
Treatife of Phyfic by Zimmerman, Vol. II.
P. 128.
( 102 )
:
had only drank half a glafs of wine
in the interval. The wine probably
ftimulated the action of the nervous
ſyſtem, and incited nature, exhauſted
by abſtinence, to open the abſorb-
ent pores of the whole body, in or-
der to fuck in fome nouriſhment
from the air. Something fimilar to
this was the cafe of the negro, who,
being gibbetted alive, regularly
voided every morning a large quan-
tity of urine, but difcharged no
more till about the fame hour the
next day*; the dews of the even-
´ing at Charles Town in South Ca-
rolina, imbibed by his body, fupply-
ing a fuperabundance of fluids in the
night, and a fufficient quantity to
fupport perfpiration in the day. It
has been obferved, that "neither hogs
* Medical Tranf. Vol. II. p. 103.
nor
( 103 )
ter
*
nor beafts of burden ever drink in
Jamaica, and yet they are continu-
ally fweating. The air is fo moift,
that the abſorbing pores of thefe
animals imbibe a fufficiency of wa-
The imbibition of water
through the pores of the fkin is an
acknowledged fact" it is well
known, that perfons who go into a
warm bath, come out feveral ounces
heavier than they went in; their
bodies having imbibed a correfpon-
dent quantity of water †. Part of
the utility of medicated and vapour
baths, depends upon this principle
of imbibition by the pores: and it is
ſaid that thirſt may be allayed by
bathing in warm fea water, the pores
G 4
Treatife of Phyf. Vol. II. p. 101.
im-
+ Goldfinith's Hift. of the Earth, Vol. I.
p. 238-398.
( 104 ).
1
imbibing the water, and carrying it
to the inteftines, but not fuffering
the diffolved falt to accompany the
water.
With refpect to the quantity of
water fufpended in the whole atmo-
fphere, or even in a column of the
atmoſphere, of a definite bafis, in-
cumbent on any particular fpot, it
cannot be aſcertained with precifion,
unleſs we knew fome method of de-
priving the air of all the water it
contains, and could at the fame time
make the experiment at different
diſtances from the furface of the
earth. For it is not only probable,
that a cubic yard of air, contiguous
to the furface of the earth, contains
at different times very different
quantities of water, even at the fame
place, according as the ground is
moift
( 105
()
105 moiſt or dry, or the temperature of
the weather warm or cold; but we
have great reaſon to believe, that at
the fame inftant of time, a cubic
yard of air, which touches the furface
of the earth, contains as much wa-
ter as three or four cubic yards,
which are fituated at the diftance of
thirty or forty yards above it. For
the water which riſes from the fur-
face of the ocean, from the perfpi-
ration of organized bodies, whether
vegetable or animal, or from the
mere action of the fun on a moiſt
earth, in being diffolved in the air as
foon as it rifes, makes the air near
the ſurface heavier than that which
is at a diſtance from it, and on that
account the motion of the air, unless
it be violent, will not readily mix
the lower and heavier air with the
higher
( 106 )
higher and lighter, and the lower air
will confequently contain more water
in a definite bulk, than the higher.
To what has in a former Effay been
obferved on this fubject, the follow-
ing illuftration may be added. If
into a deep drinking glafs half full
of water, you gently pour a glaſs of
port or claret, you will fee the wine
mixing indeed itfelf flowly with the
water, but that part of it which is
near the water, will be much more
impregnated, in any definite portion
of time, with water, than the more
remote parts, it will be a confider-
able time before the water will be
uniformly diffufed through the wine,
if they are left undisturbed; nor
does a gentle undulating motion
foon mix them, and this difficulty of
mixing them would be ſtill much
greater,
( 107 )
1
greater, if there was a greater dif
ference in their refpective weights,
or if the upper parts of the wine were
lefs denſe than the lower. Now this.
is the cafe in the air, which is not
only above 800 times lighter than
water, but its parts, which are far
removed from the furface, are much
lefs denfe than thofe which are con-
tiguous to it. That denfe air holds
more water in folution than rarefied
air, is proved from hence; that when
common air is rarefied under the
receiver of an air-pump, a part of
the water which is contained is pre-
cipitated, in the form of dew; this
anſwers to the precipitation of falt
from a faline folution, when part of
the water is taken away, which held
the falt in folution. Hence, as cold
tends to render the air more denfe,
I
it
( 108 )
it certainly contributes to its holding
more water in folution than it would
do, if it was more rarefied under the
fame degree of heat: but as hot air
diffolves more water than cold air,
and as air is rarefied by heat, it is
evident, that the denfity and heat of
the atmoſphere in fome meaſure
counteract each other, with reſpect
to the power the air has in diffolving
water: the law according to which
this power varies, in different de-
grees of heat and condenſation, is
not determinable from any experi-
ments which have yet been made.
It may not be improper to take
notice, in this place, of an objection
which is ufually made to the doctrine.
here advanced,- of water being
fufpended in the air by folution-It
is afferted, that water is as evapor-
able
( 109 )
able in an exhauſted receiver, where
there is no air, as in the open air *
It is certain, that heat will evaporate
water, and great degrees of it may,
probably, evaporate it faſter in vacuo
than in the open air, inafmuch as
the preffure of the air may tend to
obftruct the action of the heat, in
converting the water into vapour.
Thus, quickfilver is not, I appre-
hend, evaporable in the open air, yet
it has long been remarked to be
evaporable in vacuo, as may be col-
lected from the little globules of
quickfilver, generally found adher-
ing to the upper part of a barome-
ter, and which arife from the vapour
which infenfibly efcapes from the
furface of the quickfilver in the
tube.
* Berlin Mem. 1746. Waller de Afcen.
Vapo. in vacuo.
( 110 )
tube. But though heat may be one
caufe of the evaporation of water,
the attraction between air and water,
upon whatever principle it depends,
may be another. The fact moreover,
upon which the objection is found-
ed, is very queftionable, and not ge-
nerally to be admitted. A china
faucer, which contained 3 ounces of
water, loft nothing of its weight un-
der an exhaufted receiver in the
fpace of 4 hours; whilft a fimilar
faucer, containing an equal quantity
of water, loſt, in the fame time, in
the open air, one drachm and eight
grains; the heat of the atmofphere
being between 48 and 50 degrees *.
Many readers are gratified with
feeing the general progrefs of any
philo-
* See Dr. Dobfon's ingenious Obferva-
tions in Philof. Tranf. 1777, p. 256.
( III )
philofophical opinion, from its being
first fuggefted, till its being general-
ly admitted.
of philofophy, is one of the moſt
pleafing purſuits which a fpeculative
mind can be engaged in, but it re-
quires great leiſure and ability to
cultivate it with fuccefs. It is not
every diftant hint which he throws
out, that can intitle a philofopher to
the credit of being the firft framer
of an hypothefis; nor on the other
hand are we haftily to reject the
maxim, that "all novelty is but ob-
livion," inasmuch as we frequently
fee old opinions putting on the ap-
pearance of new difcoveries, from
their being dreffed out in a new
form.
The hiftory, indeed,
Natural philofophy principally
confifts in exploring, by experiment,
the
( 112 )
the phenomena refulting from the
mutual action of different bodies
upon each other. Theſe phenomena
are innumerable, no arithmetic can
reckon up the various ways in which
terreſtrial bodies may, by natural or
artificial means, be brought to ope-
rate on one another. To this cauſe
may we attribute the immenfe num-
ber of volumes on experimental phi-
lofophy, which have been publiſhed
in Europe fince Bacon pointed out
the proper method of ftudying na-
This circumſtance, joined to
the uniformity which muft ever at-
tend the operations of nature in
fimilar circumſtances, may juftly in-
title different men to the honour of
having made the fame diſcoveries,
it being much eaſier to make an ex-
periment, which may have been
made
ture.
( 113 )
made before, than to read all that
has been written in different ages
and countries on natural appear-
ances.
Doctor Halley, in the year 1691,
propoſed to the Royal Society, his
opinion concerning the origin of
fprings in this tract he expreffes
himſelf in the following manner:
"The air of itſelf would imbibe a
certain quantity of aqueous vapours,
and retain them like falts diffolved in
water, the fun warming the air, and
raifing a more plentiful vapour from
the water in the day time, the air
would fuftain a greater portion of
vapour, as warm water would hold
more diffolved falts, which upon the
abfence of the fun, in the nights,
would be all again diſcharged in
dews,
VOL. III.
H
( 114 )
dews, analagous to the precipitation
of falts on the cooling of liquors.'
M. Le Roy publiſhed an ingeni-
ous differtation on the folubility of
water in air, in the year 1751; among
other experiments, by which he illuf-
trated his hypothefis, he obferves,
that if a large, new, hollow, globular
glafs veffel, with a narrow neck, be
cloſely corked up in a clear hot day,
the water contained, in the apparent-
ly dry air, will be precipitated, and
form a dew in the infide of the veffel,
whenever the veffel is cooled, and
that this dew will vaniſh, being re-
diffolved by the air included in the
veffel, as ſoon as the air regains its
heat.
Doctor Franklin further illuſtrated
this principle, of water being foluble
* Philof. Tranſ. No. 192.
in
(115)
in air, in a paper which was read be-
fore the Royal Society in 1756, and
afterwards printed in his works*.
In the French Encyclopedie, pub-
lished in 1756, we meet with the
following paffage-on voit par la
combien fe trompent ceux qui s'
imaginent que l'humidite qu'on voit
s'attacher autour d'un verre plein
d'une liqueur glacee eft une vapeur
condenfee par le froid: cet effet, de
meme que celui de la formation des
nuages de la pluie, et de tous les
meteors aqueux, eft une vraie preci-
pitation chimique, par un degre de
froid qui rend l' air incapable de
tenir en diffolution toute l'eau dont
il s'etoit charge par l'evaporation
dans un tems plus chaud; et cette
precipitation eft precifement du
H 2
* Franklin on Elec. p. 182.
meme
( 116 )
5
meme genre que celle de la creme de
tartre, lorſque l'eau qui la tenoit en
diffolution s' eft refroidie*.
Mufchenbroek, amongſt other caufes
which he affigns for the fufpenfion
of vapour, evidently alludes to the
folution of water in air, and com-
pares it to the folution of falts in
water.†
But though a great many philo-
fophers had fpoken of the folubility
of water in air, before Doctor Hamil-
ton, yet in juftice to him it muſt be
owned, that no one has treated the
ſubject more diſtinctly, or applied it
more fucceſsfully to the explanation
of various phenomena than he has
done, in an effay which was read to
the
* Ency. Fran. T. VI. p. 283. Fol. Ed.
Introd. ad Phil. Nat. Vol. II. p. 965,
pub. 1769.
( 117 )
the Royal Society in 1765, and after-
wards publiſhed with other effays,
by the fame author.* The reader
will be very well pleafed with feeing
this principle illuftrated in an effay
by Mr. White, publiſhed in 1771,
in the elegant collection of Georgi-
cal Effays by Doctor Hunter.
* Philo. Effays by Hugh Hamilton, D. D.
F. R. S.
† Georgical Effays by Doctor Hunter,
Vol. II. p. 15.
H3
دی
ESSAY
ESSAY IV.
OF COLD PRODUCED DURING THE
EVAPORATION OF WATER, AND
THE SOLUTION OF SALTS.
O
Nthe 27th of March 1779, when
the weather had been for fome
time very dry, I put a thermometer
into a glass of water, which had
been heated to 87 degrees, by ftand-
ing expofed to the direct rays of the
fun. The thermometer was then
taken out, and its bulb was held op-
pofite to the fun, which fhone very
H 4
bright;
( 120 )
bright; as the bulb grew dry by the
evaporation of the water, the mer-
cury in the thermometer funk very
faft; it continued for a moment fta-
tionary at 76 degrees, and then it
roſe rapidly to 90; fo that 11 de-
grees of cold had been produced
during the evaporation of the water.
On another day in the fame month,
when the heat in the fhade was 68
degrees, I put a thermometer into a
glaſs of water, it ſtood at 50 degrees;
upon taking it out, the mercury in-
ftead of finking from the effect of
evaporation, began immediately to rife
from the effect of the heat of the
atmoſphere upon it. I put the ther-
mometer into the fame water, heat-
ed to 55 degrees, and taking it out,
the mercury continued ftationary for
fome time, and afterwards it began
to
( 121 )
to rife. It was put into the fame
water heated to 58 degrees, and up-
*
on being taken out, the mercury did
not either rife or continue ſtationary,
but it funk one degree; when the
water was heated to 60 degrees, the
thermometer upon being taken out,
funk 3 degrees before it began to
rife. Thefe experiments were all
made in the fhade, and it ſeems as if
we might conclude from them, that
57 was the degree of heat in the wa-
ter, in which the cold produced by
evaporation, was juft equal to the
heat produced by the atmoſphere
which then ſurrounded the ball of
the thermometer.
The degree of cold produced by
evaporation, depends, probably, up-
on the quickness with which that is
accomplished: now the quicknefs
with
( 122 )
with which water, of a definite tem-
perature, is evaporated, is influenced,
partly by the degree of heat prevail-
ing in the atmoſphere; partly by
the wind blowing upon the thermo-
meter; partly by the dryneſs or
moiſtneſs of the air; and by other
cauſes.
September 30th of the fame year,
when the heat in the fhade was 64
degrees, and the heat of the water
60, the thermometer upon being
taken out, ſtood ſtationary for three
minutes, and then it rofe; there was
a gentle fouth wind. On the next
day there was a cold dry wind from
the north, the water and air were
both at 56 degrees, and the thermo-
meter on being taken out funk to 52.
Spirits of wine, ether, and many
other fluids, produce cold by being
eva-
( 123 )
evaporated, and they produce a much
greater degree of cold than water, in
confequence, probably, of their be-
ing more evaporable. Thus, vitrio-
lic ether, which is one of the moſt
volatile fluids in nature, has been
obferved to lower Reaumur's ther-
mometer 40 degrees below the freez-
ing point (which anfwers to go de-
grees of Fahrenheit's fcale). The
experiment is most commodiouſly
made, by applying a piece of fine
linen wetted with ether upon the
bulb of the thermometer, accelerat-
ing
Ether is made by diftilling a mixture of
fpirits of wine and oil of vitriol.-Ether may
be made alfo by diftilling fpirits of wine with
the feveral acids of nitre, fea falt, and vinegar,
and it is then called the nitrous, marine, acetous
ether.
Chem. Dict. art. Ether. Or Manuel
de Chymie, par. M. Baumé, p. 375.
%
( 124 )
ing the evaporation by blowing on
the linen with a bellows, and moiſt-
ening the linen as it becomes dry,
or exchanging it for a fresh piece
which is wetted with ether. Who-
ever attempts to aſcertain the degrees
of cold refpectively produced by dif
ferent fluids, would do well to re-
mark particularly the ftate of the
atmoſphere with respect to other cir-
cumftances, as well as to its heat.
Sailors have a cuftom, in a calm,
to hold a wet finger up into the air,
and if one fide of it, in drying, be-
comes colder than another, they ex-
pect wind from that quarter. This
cuſtom is not without its foundation;
for an almoſt infenfible motion of
the air, will evaporate the water
from one fide of the finger fooner
than
( 125 )
than from another, and thus pro-
duce a degree of cold.
There is a fimilar experiment, by
which any one may convince himſelf
that cold is produced by evapora-
tion; let him wet a finger by putting
it in his mouth, and then hold it up
in the air, even in a warm room
where there is no current of air, he
will find that it grows cold as it be-
comes dry by the evaporation of the
humidity.
"The method our gentlemen make
ufe of to cool their liquors, is to
wrap a wet cloth round the bottle
and ſet it in the land wind: and,
what is very remarkable, it will cool
much fooner by being expofed thus
to this burning wind, than if you
take the fame method, and fet it in
the
126)
the cold fea-breeze."*-The cold
is produced by the evaporation of
the water from the wet cloth, and as
the bot land-wind will evaporate the
water fooner than the cold fea-breeze,
it is not to be wondered at, that the
liquor is fooner cooled when placed
in the former wind than in the latter.
"Kempfer relates, that the winds
are fo fcorching on the borders of
the Perfian gulph, that travellers are
fuddenly fuffocated, unleſs they co-
ver their heads with a wet cloth;
but if this be too wet, they immedi-
ately feel an intolerable cold, which
would become fatal to them if the
moiſture were not fpeedily diffipated
by the heat."
The cold, which is
pro-
* Ives's Voy. p. 77.
Treatiſe of Phyfic by Zimmerman, Vol
II. P. 151.
( 127 )
produced by the act of evaporation,
ceaſes as foon as that is finiſhed, by
the cloth becoming dry.
The manner of making ice in the
Eaſt Indies, has an evident depend-
ence on the principle of producing
cold by evaporation here mentioned.
On large open plains the ice makers
dig pits about 30 feet fquare and 2
deep; they ftrew the bottoms of
theſe pits, about eight inches or a
foot thick, with fugar canes, or with
the dried ſtems of Indian corn.
Upon this bed they place a number
of unglazed pans, which are made of
fo porous an earth, that the water
penetrates through their whole fub-
ftance. Theſe pans, which are
about a quarter of an inch thick,
and an inch and a quarter deep, are
filled, towards the duſk of the even-
1
ing
( 128 )
ing in the winter feafon, with water
which has been boiled, and then left
in that fituation till the morning,
when more or lefs ice is found in
them, according to the temperature
of the weather; there being more
formed in dry and warm weather,
than in that which is cloudy, though
it may chance to be colder to the
feel of the human body. Every
*
thing in this procefs is calculated
to produce cold by evaporation; the
bed on which the pans are placed,
fuffers the air to have a free
paffage to their bottoms, and the
pans, in conftantly cozing out
water to their external furface, will
be cooled in confequence of that
water being evaporated by a gentle
ſtream of warm dry air, the power
* Philof. Tranf. for 1775, P. 252,
of
the
( 129 )
the air to evaporate water depending
much upon its warmth and dryneſs.
They have a kind of earthen jar
in fome parts of Spain, called Buxa-
ros, which are only half baked, and
the earth of which is fo porous, that
the outfide is kept moift by the wa-
ter filtering through; though placed
in the fun, the water in the pots re-
mains as cold as ice*: and it probably
is colder from the jar being placed
in the fun, becauſe the evaporation
is thereby increaſed.
The Blacks at Senegambia have a
fimilar method of cooling water.
.66
They fill tanned leather bags with
it, and hang them up in the fun;
the water oozes more or lefs through
the leather, fo as to keep the out-
ward ſurface of it wet, which, by its
* Swinburne's Trav. p. 305.
I
VOL 111.
quick
( 130 )
quick and continued evaporation,
occafions the water within the bag
to grow confiderably cool *."
It is common enough for labour-
ing people, in the height of fummer,
to drink ſeveral quarts of beer or
other beverage in a day; this quan
tity is principally diſcharged from
the body by perſpiration; and the
cold which is generated during the
evaporation of the fweat, greatly
contributes to keep the body cool.
Thus has Providence contrived to
render the heat of the torrid zone
leſs inſupportable to the inhabitants;
an intenfe heat bathes the body in
fweat, but the fweat being evaporated
by the fame heat which occafioned
it, a degree of cold is generated on
Philof. Tranf 1780, p. 486.
the
(131)
the furface of the body, which would
not otherwiſe have been produced.
It ſeems reaſonable to attribute
the cold, which is produced in theſe
and other fimilar circumftances, to
the evaporation of the water, rather
than to any other caufe; becauſe
when the bulb of a thermometer is
wetted with different fluids, the cold
produced has a manifeſt dependence
on the evaporability of the Auid
with which it is wetted. Thus,
more cold is produced when the
thermometer is wetted with fpirits
of wine, than when it is wetted with
water, becauſe fpirits of wine are
more evaporable than water; and
more is produced when it is wetted
with ether than with ſpirits of wine,
becauſe ether is more evaporable
than ſpirits of wine. No cold is pro-
duced
I 2
( 132 )
duced when the thermometer is
fmeared with linfeed oil, or other
oils of a fimilar nature, becauſe theſe
oils are not fenfibly evaporable in
the ordinary heat of the atmoſphere.
Strong acid of vitriol, when expoſed
to the air, inſtead of lofing any thing
of its weight, acquires an increaſe,
by attracting the humidity of the
atmoſphere; and as ftrong acid of
vitriol, when mixed with water, ge-
nerates a degree of heat, fo the bulb
of the thermometer, when wetted
with ſtrong acid of vitriol, inſtead
of being cooled, is warmed, and the
mercury afcends, in confequence of
the heat produced from the union
of the acid of vitriol with the water
contained in the air.
When water is refolved into va-
pour, by the violence of a fall from
a con-
(133)
a confiderable height, the air will
diffolve it ſooner; and, in diffolving
it fooner, it will, probably, produce
more cold than it would have done,
if the ſurface of the water had not
been broken: hence natural and arti-
ficial cafcades may, probably, be fer-
viceable in cooling the air furround-
ing them. This obſervation is pur-
pofely expreffed in different terms,
becauſe, having more than once ſprin-
kled the floor and fides of a room
with water in the fummer - time,
when the heat of the air in the room
and of the water was 68 degrees, I
could not obferve that a thermometer,
hung in the middle of the room,
changed its degree of heat whilſt
the room grew dry. In very hot
climates the effect may, probably, be.
different; thus we are told, that in
the
1 3.
( 134 )
1
the iſland of St. Lewis, in the river
Senegal," water poured on the floor
of a room for the purpoſe of cool--
ing the air, is dried up in an inſtant,
and there is fome effect on the thermo-
meter placed in fuch a room *.'
This phenomenon of producing
cold by evaporation, had been men-
tioned by M. Amontons in the year
1699 t. It had been noticed alfo by
M. Mairan in 1749‡, and by Muſſ-
chenbroek, in his Effai de Phyſique..
Profeffor Richman, at Peterſburgh,
gave an account of feveral experi-
ments, which he had made on this
ſubject in 1747 and 1748 ||, but he
* Philof. Tranf. 1780, p. 485.
did
+ Mem. de l'Acad. des Scien. à Paris,
1699.
Differtation fur la Glace.
Novi Comment. Petrop. Tom. I. for
3747 and 1748.
( 135 )
did not explain the finking of the
mercury in the thermometer, whilft
its bulk grew dry, on the principle
of evaporation. Dr. Cullen has very
particularly illuſtrated this principle,
in a paper publiſhed in 1756; and
he has there fhewn, that the cold
produced was greater, when the
evaporation was made in vacuo,
than in the open air *. Laſtly, Pro-
feffor Braun, to whom the world is
indebted for the difcovery of freezing
quickfilver, has made a further in-
veſtigation of this matter, by pub-
liſhing a table of the degrees of cold
produced during the evaporation of
different fluids.
During the folution of falts in wa-
* Effays, Phyfical and Literary, Vol. II
Edinb. 1756. p. 145.
† Novi Commen. Petrop. Tom. X. 1.764..
L. 4
ter.
( 136 )
ter, either cold or heat, is generally
produced, but more commonly cold..
Fixed alkaline falts, Glauber's falt,.
and white vitriol, produce fmall de-
grees of heat during their folution.
Sal ammoniac produces the greateſt:
degree of cold, of any falt hitherto
known.
When Fahrenheit's thermometer
ſtood at 68 degrees, both in the
open air, and in the water which was
uſed for the experiments, I faturat-
ed equal portions of water with fal
ammoniac, with faltpetre, and with
fea falt. The fal ammoniac made
the mercury fink from 68 to 42 de-
grees, hence 26 degrees of cold
were produced; the nitre produced
17 degrees, and the fea falt produced
only 2 degrees of cold. I repeated
the experiment with the fea falt feve-
ral:
( 137 )
ral times, and with different forts of
it, but I could never obſerve that it
produced above 2 or at moft 2 de-
grees of cold. The experiments
with fal ammoniac and faltpetre
agree very well with thofe made by
M. Eller, and mentioned in the Ber-
lin Memoires for 1750; fince he pro-
duced almoſt 27 degrees with fal
ammoniac, and 18 with fältpetre.
Boerhaave, indeed, made the ther-
mometer defcend through 28 de-
grees, by diffolving fal ammoniac in
water; but he had reduced his falt
to a very fine powder, and dried it
well before he uſed it; and a differ-
ence in the fineneſs of the powder to
which the falts are reduced before
they are diffolved, may make a dif-
ference of a degree or two in the
cold produced; for the finer the falt,
ît
the
( 138 )
the more furface has the water to act
upon, and the quicker will the folu-
tion be performed; and as the cold
is produced only by the act of folu-
tion, the fooner that is accompliſh-
ed, the less effect will the heat of the
atmoſphere have, in reftoring to the
water, during the time of the folu-
tion, any part of the heat it may
have been deprived of, during the
immediate action of the water upon
the ſalt.
Does any given kind of falt, dur-
ing its folution in water, produce the
fame number of degrees of cold,
whatever be the temperature of the
water before folution? I have only
endeavoured to refolve this queſtion.
with reſpect to fal ammoniac, and it
ſeems to me that the quantity of cold:
produced, is not influenced by the
tempe-
( 139 )
temperature of the water. In the
ſummer ſeaſon, when the temperature
of the air, water, and fal ammoniac
were each of them 70 degrees, the
water fank during the folution of as
much fal ammoniac as would fatu-
rate it, to 44 degrees, or through 26
degrees. I thawed fome fnow in
winter, the thermometer ſtood in the
fnow water at the freezing point, or
at 32 degrees; by putting fal ammo-
niac, which was equally cold, into.
the water, the thermometer defcend-
ed during ſolution to fix degrees, or
through 26 degrees.
The poffibility of freezing water
in the middle of fummer, is rightly
enough inferred from this experi-
ment. In a tub, ſuppoſe of 3 feet in
diameter, place a bucket, a little
taller than the tub, of 1 foot in dia-
meter;
( 140 )
meter; in the bucket hang a Florence
flaſk, or a flat lavender water bottle,
fo that the mouth of the bottle may
be above the rim of the bucket: fill
thefe veffels with water heated, fup-
poſe, to 70 degrees. Saturate the
}
water in the tub with fal ammoniac,
then will the 70 degrees of heat be
reduced to 44, the water lofing, dur-
ing the folution of the falt, 26 de-
grees.
The water in the bucket
being furrounded with this cold fluid,
will itſelf be cooled; fuppofe it to
be cooled only to 50 degrees, then
by faturating it with fal ammoniac,
it will lofe 26 degrees more of its
heat, and be cooled to 24 degrees.
The water in the bottle being im-
merſed in a fluid, heated only to 24-
degrees, will foon be cooled below
the
(141)
the freezing point or 32 degrees, and
confequently will concrete into ice.
The cold, in all theſe cafes, is ge..
nerated only during the time of the
folution. The water recovers the
temperature of the atmoſphere fooner
or later, according as its quantity is
lefs or greater, and as the furface ex-
poſed to the air is greater or lefs; it
is here fuppofed, that the heat of the
atmoſphere remains the fame. The
different degrees of cold produced
by different falts, do not depend up-
on any general cauſe which has yet
been diſcovered, nor is there any
very fatisfactory reafon given for
theſe, and other fimilar productions
of cold or heat. The time may come
when we fhall be able to compre-
hend the reaſon why the acid of ni-
tre has fuch different effects when
mixed
( 142 )
(142
mixed with fnow from what it has
when mixed with fnow water; when
mixed with fnow water, it excites a
very great degree of heat; and when
mixed with fnow, it produces the
greateſt degree of cold that has ever
yet been obferved *. Rerum natura
facra fua non fimul tradit. Initiatos nos
credimus, in veftibulo ejus hæremus.
Illa Arcana non promifcuè nec omnibus
patent; reducta et in inferiore Sacra-
rio claufa funt. Ex quibus aliud hæc
etas, aliud quæ poft nos fubibit, adfpi-
ciet.
* Vol. I. p. 267.
ESSAY
ESSAY
V.
OF THE DEGREES OF HEAT IN WHICH
WATER BEGINS TO PART WITH ITS
AIR, AND IN WHICH IT BOILS.
T
HE air bubbles, which in fum-
mer time adhere to the infides
of decanters, water glaffes, and other
veffels filled with water, cannot have
eſcaped the obfervation of any one;
I have endeavoured to afcertain the
degree of heat in which thefe bub-
bles begin to be formed.
3
Into
( 144 )
Into a water glafs filled with wâ-
ter I immerſed a thermometer; the
heat of the water was 64 degrees;
the water was fet in a cloſet, where
the fun never fhone, for two days;
the heat remained much the fame
during that period, and there was no
appearance of bubbles. The glafs,
with the immerfed thermemeter,
was then fet in the fun, and when
the heat amounted to about 90 de-
grees, feveral air bubbles were found
adhering to the graduated fide of the
thermometer, and fome were begin-
ning to be formed on the bottom
and fides of the glaſs.
Having frequently feen the in-
fides of veffels containing water,
ftudded with bubbles, when the heat,
it was apprehended, was much lefs
than 90 degrees; I put a thermome-
ter
*
( 145 )
ter into a water-glaſs at a time when
it abounded with bubbles, and found
that the heat of the water was not
above 64 degrees.
The refult of this experiment be-.
ing very different from that of the
preceding, in which the air did not
begin to ſeparate itſelf from the wa-
ter till the heat was about 90 de-
grees, I was for ſome time at a lofs
how to account for the difference;
recollecting, however, that the water,
which required 90 degrees of heat
before it parted with its air, was
pumped from a well fed by a ſtream,
which had run four miles in the
open air; and that the other water,
which let go its air at 64 degrees,
was pumped from a well fed by
fubterraneous fprings, I attributed
the difference in the degree of heat
K
requi-
VOL. III.
( 146 )
requifite to make theſe waters part
with their air, to the different quali-
ties of the waters.
In order to try theſe waters under-
fimilar circumftances, two water-
glaffes were filled, one with common
well-water, another with that which
had been fupplied by the ſtream;
on being expoſed to the air, bubbles
began to be formed in the well wa-
ter when the heat amounted to 60
degrees, the other did not part with
any of its air in the fame degree of
heat.
I was at firft difpofed to think,
that theſe experiments pointed out a
general difference between river wa--
ter and well water, with refpect to
their difpofition for retaining or part-
ing with their air; but the following
experiment, made at a different fea-
3
fon
( 147 )
(147
fon of the year, convinced me that
the conjecture was not well founded.
In November, when the heat of
the air had been for fome time about
50 degrees, I took three water-glaffes,
one was filled with rain water imme-
diately after it had fallen, another
with the common well water, the
third with the water which came
from the ſtream: the heat of theſe
feveral waters was the fame, namely
48 degrees: they were all gradually
warmed, by fetting the water-glaſſes
in hot water, and they all began to
exhibit bubbles when the heat was
about 60 degrees; I thought the rain
waters fhewed the moft bubbles.
Hence it is plain, that the ftream
water does not differ from rain or
well water, except accidentally, as to
the degree of heat in which it parts
K 2
with
( 148 )
with its air. The first experiment,
in which the bubbles were not form-
ed till the heat was 90 degrees, was
made after there had been ſeveral
days of very hot weather, and the
water in being expofed, during its
courſe, to the action of the fun, had
probably loft a confiderable portion
of its air before it arrived at the
well. All river water has a vapid
taſte in fummer time, which is in
part, probably, occafioned by having
Joſt ſome of its air, in conſequence
of its being expoſed to the rays of
the fun. Water-drinkers are defirous
of having water fresh from the well,
fpecially in fummer time; and not
without reaſon, for the heat in that
eafon being generally above 60 de-
grees at our principal meal time,
he water, if it has been long expofed
to
( 149 )
to the air, muft have fuffered a
change of quality, not only from its
increaſe of heat, but from a confe-
quent lofs of a portion of its air.
The water which fupplies the warm
bath at Matlock, and which is drunk
by invalids, is 68 degrees warm;
hence it has loft a part of the air
which it would naturally contain,
and, except in very hot weather, it
does not exhibit any air-bubbles in
the decanters.
The air begins to be visibly fepa-
rated when the heat is about 60 de-
grees; but it begins, probably, to
be invifibly feparated when the heat
is much lefs and the leaft heat will
be requifite to ſeparate it, when the
weight of the atmofphere is the leaſt.
Philofophers have invented vari-
ous methods, equally conclufive, of
fhew-
K 3
( 150 )
fhewing, that water, in its ordinary
ftate, contains diffolved in it a por-
tion of air. And they have fhewn,
that water which has loft a portion
of this air, either by being frozen, or
beated, or by long continued agitation,
or by other means, has the property
of re-abſorbing as much air from the
atmoſphere as it had loft; and they
have fhewn, that this abforption is
the ſtrongeſt at firft, and becomes:
lefs and lefs powerful, as the water
becomes more and more impregnated:
with air. Theſe and ſimilar obſerva-
tions render it probable, that water
is as capable of diffolving a certain
portion of air, as it is of diffolving a
certain portion of any particular kind
of falt. The quantity of air, which
water is capable of diffolving and
retaining in folution, depends partly
upon
( 151 )
upon the temperature of the water,
partly upon the weight of the at-
moſphere, and partly, I conceive,
upon the water's purity. From theſe
circumſtances, as well as from fome
others which might be attended to
in making the experiment, it has
happened, that authors have given
very different accounts of the quan-
tity of air contained in water.
Boerhaave has an experiment *, from
which he infers, that there may be
ſeparated from water a quantity of
air equal in bulk to the water; the
experiment is ingenioully contrived,
but the conclufion, I think, is liable
to fome objections. The Abbé Nollet
fays, that water which has been pre-
viously purged of air, abforbs, in fix
days, one thirtieth of its bulk †.
* Boer. Chem. Vol. I. p. 5230
✯ Hiſt. de l'Acad. 1743.
"
Do&tor
£ 4
( 152 )
(152
Doctor Hales obtained by diftillation
one cubic inch of air from fifty-four
cubic inches of water *. Mr. Elkr
is of opinion that the portion of air
contained in water does not exceed
the 150th part of its bulk t. Dr.
Priestley found that a pint of his
pump water contained about one
fourth of an ounce meaſure of air,
that is, the bulk of the water was to
that of the air it contained, as 64 to
1 §. M. Fontana fays, that the wa-
ter of the Seine at Paris, after being
long boiled, abforbs in forty days
. one twenty-eighth of its bulk of
common air. Laftly, M. Cavallo
obferves, that in a temperate degree
of heat, and when the barometer is
about
*Veg. Stat. c. 6. † Berl. Mem. 1750.
§ Philof. Tranf. 1772, p. 248.
Philof. Tranf. 1779, P. 439-
( 153 )
about 29
inches, water abſorbs
about one fortieth of its bulk of
common air *
It has been remarked in another
placet, that the atmospherical air con-
ſiſts, in part, of fixed air; and ſome
of the moſt ſtriking differences be-
tween fixed and atmoſpherical air
were there mentioned. If a bubble
of atmoſpherical air of a definite
bulk, fuppofe it equal to eleven pints,
be expoſed to the action of a fuffi-
cient quantity of water, which has
been purged of its air by boiling,
the whole of the bubble will, in a
proper length of time, be abforbed
by the water; but when about feven
pints, or even a lefs portion, have
been abforbed, the remaining part
will
* Cavallo on Air, p. 213.
Vol. II. p. 247.
( 154 )
will refemble fixed air in this-that
a candle will not burn in it *. It is
very probable that water which has
not been boiled may have a fimilar
effect under certain circumftances.
"The wells at Utrecht are from 8:
to 20 feet in depth; it has been the
cuſtom to make ufe of pumps to
raiſe the water, and they are then
covered over with a kind of arch.
When, after a certain period of time,
the wells are opened, on any account,.
it is neceffary to leave them un-
covered for 12 hours, before any
perfon deſcends into them; whoever
fhould venture to go down into
them fooner, would expofe himſelf
to immediate death. The air of
thefe wells extinguishes candles like
that acquired from fermentation or
effer-
* Philoſ. Tranſ. 1774 P. 247-
( 155 )
effervefcence *." — Stagnating air,
which has brooded, though but for
a ſhort time, even over running wa-
ter, is found to be fo greatly altered
in its quality, that it will extinguiſh
flame, though it be fufficiently pure
to ſupport animal life. I was in-
formed of this fact by a miner in-
Derbyshire, who had frequently ve-
rified it by his own experience. In
order to free a mining diſtrict from.
water, they frequently dig for miles
together fubterraneous aqueducts;
fupporting the fides and roof with.
timber or ftone. The mouths or
outlets of thefe aqueducts or foughs,
being below the level of the diftrict
to be drained, there is a conſtant
ſtream of water flowing through
them. Theſe foughs are many of
them
*Lavoifier's Effays, p. 118.
(156)
!
them high enough for a man to
walk upright in them, the water
reaching to his middle or higher;
and men with lighted candles fre-
quently walk through them from one
end to the other, in order to prevent
obſtructions; it fometimes however
happens, that by the falling in of the
roof, or other accidents, the fough is
in part dammed up: when this is
the cafe, the water beyond the place
where the obſtruction is, rifes to the
roof of the fough, and thus prevents
a circulation of air, though there is
ftill a diſcharge of water through
the mouth of the fough. When an
accident of this kind happens, men
are fent with candles in their hands
to find out and remove the ob-
ftruction, but before they have walk-
ed fifty yards from the mouth of the
fough,
( 157 )
Tough, the candles go out, though
they perceive no difficulty in breath-
ing, and this extinction of the can-
dles will take place in 24 hours af-
ter the ſtoppage of the water has
commenced.
Fahrenheit, Boerhaave, and other
philofophers, had obferved, that the
degree of heat, requifite to make
water boil, was variable according to
the purity of the water, and the
weight of the atmoſphere. Within
the ufual limits of 28 and 31 inches
in the barometer, Boerhaave was of
opinion, that there would be a va-
riation in the heat of boiling water,
amounting to 8 or 9 degrees. This
fubject has of late been examined
with great accuracy by Mr. de Luc,
and Sir George Shuckburg; and Mr.
• Chem. Vol. I. p. 171.
Cavallo
( 158 )
Cavallo has given us the refult of
their experiments in the annexed
table, which is formed according to
the ſcale of Fahrenheit's thermome
ter *.
TABL E.
Height of the
Heat of boiling water
according to
Barometer. Mr. de Luc Sir G. Shuckburg
Parts of
Parts of a
a Deg. deg.
Deg, deg.
26
205,17
204,91
2 2 2
26/1/
206,07
205,82
27
206,96
206,73
27/
207,84
207,63
28
208,69
208,25
28/1/
209,55
209,41
29
210,38
210,28
29/12/
210,2
211,15
30
30/1/2
212
212
31
212,79
213957
* Cavallo on Air, p. 215.
212,85
213,69
The
( 159 )
The following experiment is curi-
ous in itſelf, and it illuftrates both
the nature of boiling in general, and
what is here advanced relative to
the heat of boiling water under dif-
ferent preffures of the atmoſphere.
I hit upon it many years ago, when
I had another object in view. My
defign was, to exhibit a ftriking in-
ftance of the increaſe of dimenfions
produced in fluids by various de-
grees of heat in order to this, I took
a large glafs veffel, refembling in
ſhape fuch mercurial thermometers
as have a bulb at the bottom *; the
bulb of this veffel held above a
gallon, and the ſtem had a ſmall dia-
meter, and was above two feet in
length. Into this veffel I poured
boiling
A veffel of this fhape is ufually called a
Matrass.
( 160 )
boiling water, and having filled it
up to the very top of the stem, I
corked it with a common cork as
clofe as I could. The water and
the cork were at firft contiguous to
each other; but in a very little time
the water began to grow cold, and as
it grew cold, it contracted itſelf and
funk very viſibly in the ftem; and
thus the firſt intention of the experi-
ment was fully anfwered. But an
unexpected phenomenon prefented
itfelf, the water, though it was re-
moved from the fire,-was growing
cold,—and had for fome time in-
tirely ceafed from boiling, began
to boil afreſh very violently, the
bubbles were large and numerous,
and continued to afcend into the
ſpace between the furface of the wa-
ter in the ſtem, and the cork, where
they
( 161 )
they burft, for above two hours.
When a hot iron was applied to that
part of the ftem, through which the
water, in contracting itſelf, had de-
fcended, the ebullition prefently
ceaſed; it was renewed when the iron
was removed; and it became more.
than ordinarily violent, when, by the
application of a cloth dipped in cold
water, that part was cooled. There
is no great difficulty in accounting
for thefe feveral appearances: by
the finking of the water in the ftem
a kind of vacuum is left between its
furface and the cork; water and other
fluids boil with lefs degree of heat,
when the preffure on their furface is
diminished; here the preffure of the
atmoſphere is wholly removed by
means of the cork, and the water
continues to boil, though its heat be
L
VOL. III.
con-
( 162 )
(162
conftantly decreafing. The interval
between the water and the cork is
not, as will be fhewn prefently, a
perfect vacuum; it is occupied either
by the vapour of the water, or by a
fmall portion of air, or by both;
heat increaſes the elafticity of both
air and vapour, and thus augments
the preffure upon the furface of the
water, hence, the ceafing of the
ebullition on the application of the
hot iron; cold diminishes the elafti-
city of air, and condenfes vapour,
and thus, the preffure upon the fur-
face being leffened by the applica-
tion of the cold cloth, the ebullition
of the water became more violent.
When the water ceafed boiling I
poured it on the bulb of a thermo-
meter, and found that its heat was
only 130 degrees,
Another
( 163 )
Another circumftance deferving
of notice remains to be mentioned.
When the water was become cold,
it had funk through the whole ftem,
and through part of the bulb; I then
inverted the veffel which contained
it, into a tub of water, and obſerved
upon the bottom of the bulb a large
circular fpot void of water. I con-
fidered this fpot as a perfect vacu-
um, for it anſwered to the fpace
which the water, in contracting it-
felf, had deferted; and the vapour
which, whilft the water was warm,
might have been fuppofed to occupy
that space, I was perfuaded, was
condenſed by the cold: in order to
fee whether it was a vacuum or not,
I pulled out the cork, whilft it was
under the furface of the water into
which the veffel was inverted, being
certain
L 2
( 164 )
•
certain that if it was a vacuum, it
would be inſtantly filled with water,
which the preffure of the atmo-
fphere would make to afcend through
the ſtem. In fact, the circular ſpot
was greatly diminiſhed by the afcent
of the water, but never (for the ex-
periment was often repeated) taken
wholly away. What remained muſt
have contained either air, or fome
other fluid, whofe elaſticity was a
counterpoize to the preffure of the
atmoſphere, on the ſurface of the
water in the tub. It would be too
hafty a conclufion, from this circum-
ftance, to attribute the formation of
the bubbles to the particles of air,
from which water cannot be ſepa-
rated by long boiling*; for it may
be,
*Licet diu ebullierit aqua non erit aeris
expers. Muſchen. de Aqua.
( 165 )
be, that this fmall portion of air
arofe from the fubftance of the cork,
or from the air in the water of the
tub, that water having not been
boiled; or it may have been intan-
gled in the parts of the boiling water,
as it was poured into the veffel, and
not have had time to efcape before
the cork was inferted; or, laftly,
which is the leaft probable fuppofi-
tion, the vapour arifing from the
water may not be capable of being
totally condenfed.
The phenomenon of the boiling
of fluids is not very fatisfactorily ex-
plained. It is clear, I think, from
the experiment of which I have given
an account, that it cannot be attri-
buted, in all cafes, either to the
efcape of air from the interstices of
water, or to the matter of fire, as it
L 3
is
( 166 )
is called, pervading the water; for
the water continued boiling for two
hours after it was removed far from
the fire; and the air, if it contained
any, was utterly inadequate to the
formation of the numerous bubbles.
Boerhaave has remarked, that bubbles
of the kind here ſpoken of contain
no air, but he has not affigned the
cauſe of their origin: Dr. Hooke af-
cribes them to the fubtle parts of
the water, which, when the preffure
of the air is removed (probably by
means of an air pump), are able to
acquire the form of vapours, by that
fmall degree of heat which is left in
the ambient air *: and other philo-
fophers have adopted this idea,
without hinting at, what Hooke fup-
pofed,
See Birch's Hift. of the Royal Society.
The Abbe Nollet and Dr. Hamilton.
( 167 )
pofed, a different degree of volatility
in the parts of the water.
From what has been advanced we
may conclude, that the Almighty,
when he ſeparated the chaotic mafs
into air and water, did not render
theſe two oceans of matter fo wholly
heterogeneous from each other, as
that they ſhould be incapable of con-
tracting any union together; they
have, on the contrary, fuch a difpo-
fition to unite, as feems to indicate
their having had a common origin;
and were it not for the intervention
of heat, they would, probably, unite,
and again compofe a common mafs.
The water on the furface of the earth
is conftantly replete with air, and the
atmoſphere is replete with water.
The numerous tribe of aquatic ani-
mals,
L 4
( 168 )
mals, which inhabit the ocean of
water, would perish, if it contained
no air; and it is not an improbable
conjecture, that the animals which
exiſt in this ocean of air, would pe-
riſh if it contained no water. The
air, moreover, by being abforbed
into the water, and afterwards fepa-
rated from it by the action of the fun,
to which it is daily expoſed, is ren-
dered abundantly more fit for animal
refpiration than common air; and
this purified air (the quantity of
which, confidering the great extent
of the furface of the earth which
is covered with water, muft be very
confiderable) cannot but be one great
means of reſtoring to the whole maſs
of air, thofe falubrious qualities of
which it is daily deprived, by the
respi-
( 169 )
refpiration of animals, the putrefac-
tion of bodies, the combustion of fuel,
and other cauſes.*
* Dr. Priestley has obferved, "that the
fame water, which, if examined immediately,
gives only a ſmall quantity of bad air, yields
Spontaneously about ten times the quantity of
pure dephlogiſticated air, after ftanding fome
time expofed to the fun." Phil. Tranf. 1779,
P. 377. An animal will live five times as long
in what is called here dephlogiſticated air, as
it will in common air of the beſt quality.
..h
ESSAY
ESSAY VI.
OF WATER IN A SOLID STATE; OF
THE HEAT OF SPRING WATER;
AND OF A PROBABLE CAUSE OF
THE IMPREGNATION OF SULPHU-
REOUS WATERS.
TH
HE mind of man admits with
great reluctance, the truth of
every teftimony concerning matters
of fact, which happen to be repug-
nant to the uniform experience of
his fenſes; hence the general back-
wardness
4
( 172 )
wardness to believe the miracles re-
corded in the bible; and hence the
Dutchman who informed the king of
Siam, that water in his country
would fometimes, in cold weather,
be fo hard that men walked upon it,
and that it would bear an elephant,
if he were there, was efteemed a per-
fon unworthy of credit, the king, as
Mr. Locke relates the ftory, faying to
him," Hitherto I have believed the
ftrange things you have told me,
becauſe I look upon you as a fober
man, but now I am fure you lie.”*
Mabine, the native of Borabora,
could fcarcely be perfuaded, even by
the information of his fenfes, of the
reality of the fame effect. The ap-
pearance of "white ftones," as he
called
* Locke's Effay on the Hum. Und. B. IV.
C. XV.
( 173 )
called hail, which melted in his
hand was altogether miraculous to
him; and when he had been with
difficulty convinced that an exten-
five field of ice was not common
land, he was determined at all events
to call it "white land," by way
diftinguiſhing it from all the reft*.
of
This determination of the favage
was made in the true fpirit of philo-
fophy, for ice in fmall particles is
a fpecies of earth, and in folid maſſes
it may be confidered as a kind of
tranſparent ſtone. The waters, fays
Job, fpeaking of the effect of froft,
are hid as with a stone; that is, water
conceals its nature, by affuming a
ftone-like hardneſs and confiftence
when it becomes ice. The Ruffians
* Forſter's Voy. Vol. I. p. 530.
+ Chap. xxxviii. 30.
applied
( 174 )
applied ice to the fame purpoſes
with ſtone, at the whimfical mar-
riage of Prince Gallitzen, in 1739;
an houſe, confifting of two apart-
ments, was built with large blocks
of ice, the furniture of the apart-
ments, even to the nuptial bed, was
made of ice; and the icy cannon and
mortars, which were fired in honour
of the day, performed their office
more than once without burfting.*
Ice, however, differs from all other
earths and ftones, not only in its
melting in a much lefs degree of
heat than any of them, but in its
being fubject to a conftant diminu-
tion of its weight when expofed to
the open air, in the greatest degree
of cold. It generally becomes fluid
in the 33d degree of heat, as indi-
cated
* Manftein's Mem, of Ruffia.
( 175 )
*
The
cated by Fahrenheit's thermometer;
and Mr. Boyle, by expofing in a
good balance fomewhat lefs than two
ounces of ice to a fharply freezing
air, a little before midnight, found
it in the morning diminished in
weight ten grains. " It is probable,
that this diminution of the weight of
ice, is owing to the abraſion of its
parts by the action of the air.
particles of air are thought to be
larger than the particles of water,
and may by their motion acquire
force enough to ſeparate the particles
of ice; or if this fhould not be ad-
mitted, it muſt be remembered, that
the air always contains a great quan-
tity of water, the particles of which,
when converted into particles of ice,
though in this country they are fel-
dom
* Boyle's Works, Fol. Vol. III. p. 66.
(176)
dom large enough to be feen, always
make themſelves felt by impinging
upon our ſkin: thefe icy particles
when put in motion may abrade the
ſurface of a mafs of ice, and cauſe
thereby a conftant diminution of its
weight. In confirmation of this ex-
planation it may be obferved, that
ice fuffers no lofs of its weight in a
veffel devoid of air,
veffel full of air. *
nor in a cloſe
That the icy
particles, contained in a freezing at-
moſphere, ſhould be able to act upon
ice, cannot be a matter of difficult
conception to thofe who recollect,
that the hardeſt bodies in nature.
fuffer a diminution of their weight,
by the friction of the minute parts
of the fame kind of bodies; dia-
mond
* Hamilton on the Afcent of Vapours,
p. 71.
(( 177 )
mond duft being effentially necef
fary for the cutting or polishing of
diamonds.
That water was diminiſhed in
quantity by being frozen, was known
to Hippocrates; for he expreſsly ſays,
that if a given quantity of water be
frozen, and afterwards thawed, it
will not fill the fame veffel it would
have done before it was frozen *
Pliny was of the fame opinion with
Hippocrates, and they both of them
attribute this diminution of weight to
the feparation of the more fubtile
parts of the water during congela-
tion †. The principal caufe of the lofs
of weight, fuftained by water when
changed into ice, feems to be the
inceffant
* Hippoc. de Aqua.
Plin. Hift. Nat. Lib. II. S. 61. & Lib.
XXXI. S. 3•
VOL. III.
M
( 178 )
inceffant action of air upon its fur-
face; it is true, however, that water
is, by freezing, deprived of the great-
eft part of the air with which, in its
fluid ftate, it is ordinarily faturated;
and this feparation of its air may
contribute fomething towards the
diminution of the water's bulk; fince
water, when faturated with air, is
fomewhat greater in bulk than when
deprived of it.
It is eafy to apprehend, that the
lofs of weight which any given quan-
tity, ſuppoſe a cubic foot, of ice will
fuffer by expoſure to the air in a
given time, will depend, partly upon
the hardneſs or foftnefs of the ice,
partly upon the temperature of the
atmoſphere, with refpect to the de-
grees of cold and humidity, partly
upon the velocity of the wind which
brushes
3
( 179 )
brushes its furface, and probably
enough upon the agency of other
caufes with which we are lefs ac-
quainted. Some philofophers have
eſtimated, in general terms, the loſs
of weight fuftained by a certain
weight of ice, without fpecifying the
magnitude of the ice's furface; others,
with more accuracy, have mentioned
both the weight and furface of the
ice expofed to the air, but then they
have either omitted to fpeak of the
ice's confiftency, the temperature of
the atmoſphere, the force and direction
of the wind, or they have expreffed
themſelves in very indefinice terms
concerning thefe points, fo that we
cannot be faid
be faid to have hitherto
gained, from their experiments, any
precife information upon the fubje&.
As to the fact itſelf, the moſt com-
M 2
mon
( 180 )
ނ
mon obfervation is fufficient to af
certain us of its truth. In long con-
tinued frofts, the ice formed in ponds,
and other ſmall collections of water,
is fenfibly diminiſhed every day,
and often wholly evaporated; and a
fall of ſnow may be feen confider-
ably wafted in a few days, in the
fevereſt ſeaſon.
Notwithſtanding this diminution
of weight, to which both ice and fnow
are fubject in the coldeft weather, and
the thaw which they experience in
the hotteſt, yet fome have doubted
whether the quantity of congealed
water be not an increafing quantity
upon the furface of the earth; and
have even thought, that the globe
of the earth muft in proceſs of time
reſemble an egg, having its diameter
from pole to pole, longer than the
cqua.
( 181 )
equatorial diameter, on account of
the conftant accumulation of frozen
water at the two poles." After fo
many years lapfe, it cannot be, I
think, but that the diameter of the
earth from pole to pole, from the
top of the fnow at one end of the
earth, to the top of it at the other
end, is much longer, than in any
part under the equator, though at
the creation it were (as I believe)
made ſpherical *.
In ſome mountainous countries,
the proportion between the ſnow
which falls at one feafon of the year,
and that which is diffolved in an-
other, approaches fo near to an
equality, that upon the fame fpot,
the fnow may in one year be feen
quite through the year, in another,
* Childrey's Brit. Bacon, p. 148.
M. 3
the
(182)
the laſt ſpeck of it will vanish in a
few weeks or days, before a new
fupply is brought by the approach.
of winter. In colder climates, the
utmoſt power of the fummer fun is
not able to melt all the fnow which
falls in the winter. In aſcending
mount Etna, the Alps, or the Andes,
though the lower parts are found to
be rich in vegetation, yet you foon
come to a region covered, as it
fhould feem, with everlasting fnow:
the height at which this region com-
mences, does not admit much varia-
tion in the fame latitude, but is very
different in. different latitudes. It
begins at the distance of near three
miles above the level of the ſea, un-
der the equinoctial line; and at each
pole, probably, it is not removed
from that level fo many hundred
feet;
(183)
and
feet; it is found to be 600 yards
nearer to the level of the fea at Tene-
riffe than under the equator;
above 1200 yards nearer in Switzer-
land than at Teneriffe
Not only the tops of high moun-
tains in every quarter of the globe
are covered at all ſeaſons of the year
with fnow, but the ocean both in the
northern and fouthern hemifphere is,
in high latitudes, replete with im-
menfe mountains, and extenfive plains
of
The
Hifto. Nat. des Glaciers Suiffe
author fays, enfin la plupart des Montagnes
voifines des poles font couvertes jufqu'à leur
pied de neiges perpetuelles. This obferva-
tion must not be admitted without refriction,
if it be at all true, fince in Greenland, and in
the latitude 79 degrees 44 minutes north, the
feet of the mountains are in certain feafons freed
from fnow. See Crantz's Hift. of Greenland,
Vol I. p. 30. and Phipps's Voy. p. 52 and
700
M 4
( 184 )
of ice, in the greatest heats of fum-
mer; and hence it has appeared pro-
bable to many, that both the fnow
upon the land, and the ice upon the
fea, receive an augmentation every
year, from the continued agency of
the fame cauſe which first produced
them.
A philofopher, well acquainted
with the nature of the Alps, expreffes
himſelf upon this fubject in the fol-
lowing manner: "One cannot doubt
concerning the increaſe of all the
Glaciers of the Alps; for their very
exiſtence is a proof, that in preced-
ing ages the quantity of fnow which
has fallen during the winter, has ex-
ceeded the quantity melted during,
the fummer. Now not only the fame
cauſe ſtill ſubfifts, but the cold, oc-
cafioned by the mafs of ice already
formed,
( 185 )
?
formed, ought to augment it fil
farther, and thence both more fnow.
ought to fall, and a lefs quantity of
it be melted *.” If this be admitted,
the time will undoubtedly come
when the fea will be diminiſhed in::
depth, if not dried up by the con--
verfion of the water, which is daily'
raiſed from it, into fnow or ice; and
had the world been as old, as fome
are fond of fuppofing it to be, we
ſhould, probably, have had no wa-
ter upon its furface at the prefent
day. However, it must be owned,
that no argument can be drawn a-
gainst the antiquity of the world,
from this confideration, becauſe there
is reaſon to believe that the ice and
fnow upon the furface of the earth
are not annually increafing in quan-
tity.
De Luc de l'Atmoſphere, Vol. II. p.. 328.
( 186 )
tity. For, befides the heat of the air
in fummer, there is another caufe
which tends to prevent an indefinite
augmentation of congealed water-
the internal heat of the earth. The
general heat of the fprings of water,.
fituated deep in the bowels of the
earth, is 48 degrees; in mountainous
countries, I fufpect it to be fome-
what lefs, but fufficient, notwith-
ſtanding, for the purpoſe here men--
tioned. When the fnow, incum-
bent on any ſpot of ground, is but
thin, it may fo far cool the earth,
that its internal heat may not be able
to diffolve it; but when the bed is
thick enough to protect the earth
from the influence of the atmo-
fpherical cold, that furface of the
fnow which is contiguous to the fur-
face of the earth, may, even in the
coldest
(187)
coldeft winters, receive more heat
from the earth than it does cold from
the atmoſphere, and, on that fuppo-
fition, I fee no abfurdity in admitting,
that it may be diffolved at all feafons
of the year.
The fact I believe is certain, that
ftreams of water iffue from the bot-
tom of the Glaciers in the Alps, in
the greateſt feverity of winter; ſo
that whether the internal heat of the
earth be admitted, or not, as a caufe
fufficient to explain the phenome-
non, a conftant thaw of the ice or
fnow, which is contiguous to the
furface of the earth in the Alps, can--
not be denied; and this, added to
other caufes, may render it probable
that the quantity of congealed water
has its limit, even in the coldest cli
mates.
The
( 188 )
The ordinary heat of fpring water,
which does not feel the viciffitudes
of the temperature of the atmo-
ſphere, is here faid to be 48 degrees
of Fahrenheit's thermometer; it may
be worth while to add a few remarks
on this fubject.
In Auguſt 1778, when the heat of
the air was 72 degrees, I tried, on the
fame day, the temperature of feveral
fprings, reputed cold, in the neigh-
bourhood of Matlock; and I found
them varying in heat from 50 to
54 degrees. This variation, pro-
bably, proceeds from their fubterra-
neous paffages being fituated at dif-
ferent diſtances from the furface of·
the earth, which was then much
warmed by the heat of the fummer.
Or it may proceed from the fprings
being more or lefs mixed with the
water
( 189 )
189)
water which fupplies the warm baths,
the heat of that water being 68 de-
There is a fubterraneous
grees.
paffage upon the fide of the hill near
the new bath at Matlock, which ter-
minates in a large cavern, fituated
under one of the fields in the midway
between the new and the old bath;
and from this cavern, which is always
full, iffues the warm water which
fupplies both the baths; and it may
probably ooze out in different direc-
tions, and in different quantities, fo
as to make the neighbouring fprings
participate more or lefs of its warmth.
*
At Lord Godolphin's houfe on Gog-
magog hills, near Cambridge, there is
a well, above 230 feet in depth,
which is dug through a ftratum of
chalk; I have frequently examined.
the heat of the water of this well,
and
( 190 )
and conftantly found it to be 50
degrees. At Cherry Hinton, a village
fituated at the bottom of theſe hills,
there iffues from the chalk a very
copious ſpring; the heat of this water,
as it bubbles out of the earth, is, at
all ſeaſons of the year, 50 degrees.
I have tried the heat of fome deep
wells dug in chalk at Bury St. Ed-
mund's, and found it variable from
" It has
50 to 52 degrees.
been long and generally obferved,
that as far as the limestone extends,
that tract of ground makes the fnow
that falls on it, thaw or melt fooner
than it does on the neighbouring
lands *"
"This is Mr. Boyle's ob-
fervation concerning fome limestone
land in Ireland, and he fays its truth
was confirmed to him by a Derby-
*Boyle's Works, Vol. IV. p. 278.
fhire
( 191 )
Thire miner, who affured him, that
on contiguous diftricts of land, fnow
was obſerved to diffolve much foon-
er on the foil which covered lime-
ftone, than on that which covered
freeftone. If thefe obfervations may
be depended on, we may, perhaps,
in general infer, that the heat of cal-
careous ftrata is greater than that of
other kinds of ftrata, and this would
furniſh a reafon for the fprings in
chalk countries being of the warmth
of 50, though the ordinary heat
of fprings be not above 48 de-
grees.
In the middle of fummer, when
the air was 72 degrees hot, I tried
the heat of ſome fprings at Harrow_
gate in Yorkshire. Pump-water at
the Granby Inn 48 degrees. — Old
Spaw 45 degrees.- Pewit or Tewit
well
(192)
well 48 degrees.-Sulphur well · 50
degrees. The cold well at Buxton,
examined at the fame time of the year,
was 48 degrees, and the famous Spaw
at Llanrhaid'r in Denbighshire was
alfo 48 degrees; St. Winifred's well,
at Holywell in Flintshire, was con-
fiderably warmer, the thermometer,
when held in the fpring as it roſe
out of the earth, ftahding at 54 de-
grees. I have tried a great many
other fprings in different parts of
Great Britain, and found the heat of
most of them to be included be-
tween the limits of 48 and 54 de-
: grees, the mean of which is 51.
Springs on the fides of high moun-
tains may, probably, participate of
the cold which is found to be greater
in elevated than in low fituations.
There is a fpring by the fide of the
:
turn-
·
( 193 )
turnpike road leading over the high
ground called Otley Shevin in York-
fhire; I obferved the heat of this
fpring in September, when the air
was warmed to 62 degrees, to be
not 48, but only 45 degrees. The
mean heat of fprings near Edinburgh
is faid to be 47, and at London 51
degrees: this diverfity depends,
probably, on the different elevations
of London and Edinburgh above
the level of the fea.
I have mentioned the Sulphur well
at Harrowgate, according to its uſual
appellation at that place, without
taking upon me to decide the long
controverted queftion, concerning
the exiſtence of fulphur in that and
other waters of the fame kind.
"Sulphur has been long efteemed a
VOL. III.
N
* Philof, Tranf. 1775, P. 460.
mine-
( (194
194 )
mineral body very common to be
met with in waters; and all thoſe
waters which have a strong fetid
fmell, reſembling that of a foul gun,
have been esteemed to be more or lefs
impregnated with fulphur. How-
ever, Dr. Hoffman feems to doubt
much of its existence in the greater
number of fuch waters; and Dr.
Lucas has affirmed, that it is not to
be found in the form of fulphur in
any water whatever; not even in that
of Aix-la-Chapelle, where a true and
perfect fulphur is found on the up-
per parts of the conduits through
which the water paffes; for he fays,
that, ftrictly speaking, thefe waters
do not contain fulphur fubftantially
diffolved in them, but are impreg-
nated with a phlogifton and an acid,
the principles of fulphur; which be-
ing
( 195 )
ing in a volatile ſtate, are ſublimed,
meet on the ſurface of the conduits,
and there unite into a true and per-
fect fulphur, which did not naturally
exift in the water*." The author,
from whom I have made this ex-
tract, informs us, that Dr. Rutty
maintains the exiſtence of fulphur
in mineral waters; and that both Dr.
Shaw and Dr. Short found fulphur in
Harrowgate water. Notwithſtand-
ing the teftimony of fuch eminent
phyficians, the more recent opinion
of a phyſician, whom Dr. Monro con-
fulted on the fubject in 1768, is
againſt the exiſtence of fulphur in
fuch waters. "I have taken parti-
cular notice of every appearance of
the Harrowgate waters, and muſt
N 2
own
* Monro on Mineral Waters, Vol. I. p. 30.
and 196.
( 196 )
own I never obferved any appear-
ance of fulphur floating in them, nor
any fcum at the top of the well; nei-
ther could I meet with any perſon
in that quarter, who remembered the
appearance of real fulphur fublimed,
upon taking up the ftones at the
bottom of the well, as mentioned by
Dr. Neal."I beg leave to add
my own obfervation on the fubject,
which I made in 1780. The water
in the well rifes into a circular ftone
bafon; a whitish cruft adheres to
the ftone, where it is contiguous to
the ſurface of the water; I fcraped
off a portion of this cruft, and put-
ting it on a hot iron, I found that it
burned with the flame and fmell of
fulphur. I do not think that this
experiment abfolutely warrants us to
con-
* Monro on Mineral Waters, Vol. I, p. 196.
( 197 )
conclude, that actual fulphur is con-
tained in this and other waters ge-
nerally denominated fulphureous;
we juftly infer from it, that fome-
thing is fublimed from the water,
which either of itſelf is fulphur, or
which in conjunction with the air,
or fome other principle, conftitutes
fulphur.
The profecution of this fubject
would lead to fpeculations too ab-
ſtruſe for my deſign; the following
experiment, however, which I have
frequently made, will, I hope, throw
no inconfiderable light on the cauſe
of the impregnation of fulphureous
waters in general.
The acid of vitriol does not act
upon the common Derbyshire lead
ore, except when it is affifted by
heat, it then diffolves it, and a great
efcape
N 3
(198)
efcape of air is obferved; I made
this air, as it was difcharged from
the ore, paſs through a high-bended
tube into a bottle full of pump wa-
ter: the water, in a very little time,
acquired the fetid fmell of Harrow-
gate water, its tafte was the fame
as that of ſuch fulphureous waters
as contain no falt,-it was perfectly
tranfparent, but in the courſe of 24
hours it became cloudy, and loft moft
of its fmell, it did not fuffer any
precipitation by the addition of the
acid of vitriol,-filver was blackened
both by being put into this water,
and by being expofed to the vapour
which arofe from it; from all theſe
it may properly
circumſtances,
enough, I think, be called an arti-
ficial fulphureous water.
I have obferved the fame pheno-
mena
?
( 199 )
mena when, instead of lead ore, I
ufed black jack; and I remember
that once having placed a bottle,
containing black jack and acid of
vitriol, fo that its neck leaned againſt
a plastered wall, I obferved fome
days afterwards, that the wall was
ftained, to the distance of above a
foot from the mouth of the bottle,
of a purple colour, efembling the
purple fediment often found in ful-
phureous wells.
Air of the kind here fpoken of,
may be ſeparated from other fub-
tances, as well as from lead ore and
black jack, and by other means, as
well as by the acid of vitriol; and
it feems very probable, that the wa-
ters uſually called fulphureous, are
impregnated with this kind of air,
which has been feparated, in the
bowels
N 4
( 200 )
bowels of the earth, from particular
minerals, eſpecially fulphureous ones.
It has been remarked of Harrowgate
water, that as it fprings up it is clear
and ſparkling, and throws up a quan-
tity of air bubbles.
During the procefs of impregnat-
ing water with air, by diffolving lead
ore in the acid of vitriol, a part of
the glaſs tube was coated with a
thin pellicle of fulphur, which had
accompanied the air in its afcent:
May not the fulphur fublimed from
Harrowgate water, have accompani-
ed the air which gives it its fmell? Is
it certain that this kind of air does
not confift of attenuated parts of ful-
phur, which have acquired an elaftic
force, and which cannot be con-
denſed in water? Or is it not more
probable, that this kind of air is one
of
( 201 )
of the conftituent parts of fulphur,
than fulphur itſelf? Does this air,
and the inflammable air feparable
from fome metallic fubftances, by
folution in acids, confift of oleaginous
particles in an elaftic ftate?
If the reader withes to impregnate
common water with the fulphureous
properties of Harrowgate water, he
may do it in the following fimple
manner-Into an apothecary's vial,
holding four or five ounces, put
fome pounded lead ore, and pour
upon it fome acid of vitriol (there
is no occafion to be folicitous about
the proportions of the lead ore and
acid, for if there be more or lefs
ore than the acid can diffolve, ftill
air enough for the purpofe will be
difcharged); wrap a few folds of
wet linen round one end of a bended
tube,
( 202 )
tube, infert this end into the neck
of the vial fo cloſely, that no air
may pafs out of the vial except
through the tube; the end of the
tube fhould be at fome diftance
from the furface of the acid. Put the
other end of the tube into a bottle.
full of water, then, by fetting the vial
on the hot bar of a grate, or by fome
other means, heat the acid, and as
foon as it is heated, it will begin to
act on the lead ore, and a great quan-
tity of air will be diſcharged, which
will pass through the tube into the
water in the bottle, and in a few mi-
nutes the water will be ftrongly im-
pregnated with the fulphureous pro-
perties of Harrowgate water.
fides its fulphureous impregnation,
Harrowgate water contains fea falt;
and moſt other fulphurcous waters
Be..
contain
( 203 )
contain fome falt or other, ſo that
to make a complete imitation of
them, the falts which they ſeverally
hold ſhould be added, in due pro-
portion, to the water impregnated
with the air here ſpoken of.
Though I am greatly difpofed to
believe, that fulphureous waters are
impregnated with their peculiar
fmell and tafte, after the manner I
have deſcribed; yet, to affift the rea-
der's conjectures concerning the ori-
gin of this impregnation, I will men-
tion another way in which it may be
fuppofed to arife, and which will
account for the faline taſte as well as
the ſmell of the water.
I know not whether any fpecies
of maritime plants, containing fea
falt, will impregnate water with a
fulphureous fiell by means of putre-
faction;
( 204 )
faction; nor whether all of them will
do it by means of combuftion, but
that one of them will do it I can
have no doubt: I allude to the
bladder fucus or fea wrack, which is
burned on our coafts for the making
of kelp. It has been mentioned be-
fore*, that fea wrack, when burned
to a black coal, will yield, by being
boiled in water, a great quantity of
common falt; and I would now re-
mark, that the water extracts from
the black afhes, not only a great
quantity of common falt, but fome-
thing elſe alfo, by which, without
lofing its tranfparency, it acquires
both the ſmell and fulphureous taſte ·
of Harrowgate water; and by which
it is enabled, like that water, to
blacken filver and white paint.
This
{
* Vol. I. p. 137.
( 205 )
(205
That fomething I am fenfible may
be what chemiſts call liver of fulphuï,
or an union of fulphur with fixed
alkali, and it would not be difficult
to explain its formation during the
combuftion of the fea wrack; no ful-
phur however can be precipitated
from the water by the acid of vitriol,
though that acid turns it, as is the
cafe with Harrowgate water, a little
cloudy. The air extracted from iron
by the acid of fea falt, impregnates
water with a fmell fomewhat refem-
bling that of Harrowgate water, but
its difference both from the natural
and the artificial fulphureous waters,
may be eaſily diſtinguiſhed, eſpecial-
ly after the water has ſtood a few
hours expofed to the air.
ESSAY
ESSAY_VII. *
OF DERBYSHIRE LEAD ORE,
L
EAD ore, as dug out of the
mine, is generally much mixed
with ſpar, limeftone, and other ſub-
ftances, bulk for bulk, lighter than
the ore itſelf. It undergoes various
dreffings before it becomes a mer-
chantable commodity, the general
tendency of which is to free it, as
much as poffible, from every hetero-
geneous impurity.
Suppoſe
* The ſubſtance of this Effay was printed
in the Philof. Tranf. 1768.
(208)
Suppofe that a cubic foot of lead
ore, which contained no fpar or other
extraneous matter, would weigh 7800
ounces, and that a cubic foot of ſpar,
which contained no lead ore or other
foreign ſubſtance, would weigh 2700
ounces, then would a mixture, con-
fifting of a cubic foot of pure lead
ore, and a cubic foot of pure ſpar,
weigh 10500 ounces, and one cubic
foot of fuch a mixture would weigh
5250 ounces. It is obvious that
according to the different propor-
tions in which the particular kinds
of fpar and lead ore here affumed,
are ſuppoſed to be mixed together, a
cubic foot of the mixture will have
different weights, the limits of which
are on the one hand 7800, and on
the other 2700 ounces; it never can
weigh fo little as 2700 ounces, for
.3
then
( 209 )
209)
then it would confift intirely of fpar
without any lead ore; nor can it
ever weigh fo much as 7800 ounces,
for then it would confift intirely of
lead ore without any fpar.
From this view of the matter it
is evident, that the purchafing of
lead ore by the meafure, which is
the general, though not the univerfal
custom in Derbyshire, is a mode lia-
ble to fome exception; fince a difh,
containing any definite meafure, mult
have different weights according as
the ore with which it is filled is more
or lefs free from fpar. And it is
fcarce poffible, by repeated dreffings,
to feparate all the fpar from an ore,
or equal portions of it from equal
portions of ore.
There is a diverfity, however, in
the weights of equal measures of lead
VOL. III.
ore
(210)
ore which, probably, does not arife
from ſparry or other heterogeneous
accretions, but from the nature of
the ore itſelf. I have carefully cal-
culated the weight of a cubic foot of
many of the Derbyshire lead ores;
the weight of a cubic foot of the
lighteſt which I met with was 7051
ounces, and the weight of a cubic
foot of the heavieft was 7786 ounces;
the difference amounting to between
a ninth and a tenth part of the weight
of the lighteft. There are, proba-
bly, other ores of lead, the weights
of equal bulks of which differ more
than theſe here mentioned; but the
difference between thefe is fufficient
to fhew the great uncertainty of pur-
chafing lead ore by the meaſure,
fince ten diſhes of one fort of ore
may not weigh more than nine diſhes
of
( 211 )
of another fort, though both the
forts are equally well dreffed.
Lead ore is not always of the fame
goodneſs in the fame mine, nor even
in the fame part of the fame mine;
and, what is more remarkable, the
different parts of the fame lump of
ore have in equal bulks different
weights. I could not eafily have
believed this, unleſs a variety of ex-
periments had convinced me of the
fact.
They were employed lately at Holy-
well in fmelting a lead ore from the Iſle
of Man; the ore was rich in filver.
A lump of this ore, weighing about
ten ounces, was broken into feveral
pieces, and fuch of the pieces were
felected as appeared to the eye to be
wholly pure. I eftimated the weight
of a cubic foot of fix of thofe pieces,
Q 2
and
( 212 )
and found that a cubic foot of the
lighteſt kind would have weighed
6565 ounces, and a cubic foot of
the heaviest kind would have weigh-
ed 7636 ounces. Suppofing the
weight of a cubic foot of water, to
be denoted by 1000, the mean
weight of a cubic foot of the fix
different pieces of this ore, may be
expreffed by 7115 avoirdupoife
ounces.
A very pure fpecimen of teffella-
ted lead ore, from a mine near Aſh-
over in Derbyshire, was broken into
fix pieces, weighing near one ounce
each. A cubic foot of the lighteft
of theſe pieces would have weighed
7326 ounces, and a cubic foot of the
heaviest would have weighed 7786
ounces. The mean weight of a cu-
bic foot of the fix pieces was 7566.
At
( 213 )
At the fame mine they frequently
meet with fmall quantities of fteel-
grained lead ore. Six different pieces
of the fame lump of this kind of
ore were chofen, each of which ap-
peared quite free from fpar and every
other impurity. A cubic foot of the
lighteft of thefe pieces would have
weighed 7183 ounces, and a cubic
foot of the heaviest would have
weighed 7442 ounces. The mean
weight of a cubic foot of the Ex
pieces was 7342.
Other lumps of ore from different
mines, were refpectively broken into
different pieces, and fcarcely any
two equal pieces of the fame lump
were obſerved to agree in weight.
This diverfity in the weights of
equal bulks of the feveral pieces of
the fame lump of ore may be owing,
either
03
( 214 )
either to the different proportions in
which the conſtituent parts of the
ore are combined in the feveral
pieces; or to the different quantities
of extraneous fubftances impercepti-
bly mixed with them, or, which feems
moſt probable, to a diverfity in the
fize or configuration of their pores.
But be the cauſe of this diverſity
what it may, the fact, I believe, iş
certain, and by no means fingular;
for not to mention the varieties ob-
fervable in the weights of equal
bulks of different pieces of roll
brimſtone, of corrofive fublimate, of
caft fteel, and other factitious fub-
ſtances, the natural fpars generally
found along with lead ore are fub-
ject to a fimilar diverfity, though
not, perhaps, in an equal degree.
A piece of rhomboidal, otherways
I
called
(215)
called refracting or lantern Spar, was
broken into four ſmaller pieces,
the weights of a cubic foot of each
of which were 2675, 2687, 2715,
2723; the medium of the four is
2700 ounces. Mr. Cotes fixes the
weight of a cubic foot of Iceland
cryſtal at 2720, and Wallerius fixes
it at 2700 ounces.
The weights of a cubic foot of
four pieces of the fame lump of cu-
bical spar were 3204, 3218, 3222,
3231; the medium of the four is
3219 ounces. Moft of the fpars
met with in Derbyshire are either
rhomboidal or cubical; they are eafily
diftinguished from each other by
a view of their fhape, when their an-
gles can be difcerned; and when the
ſhape cannot be eaſily ſeen, the na-
ture of the fpar may be afcertained
04
by
( 216 )
by touching it with an acid; the
rhomboidal ſpar always effervefcing
with an acid, and the cubical refift-
ing its action. The lead fmelters
make great ufe of the cubical fpar as
a flux for fuch lead ores as do not
readily melt it is curious to fee its
effect; a few fhovels full of it,
thrown upon a heap of red hot ore,
immediately melting down the ore
into a liquid, though the longeſt
continuation of the fame degree of
heat, without the addition of the
fpar, would not have been fufficient
for the purpoſe.
Six ounces of fine teffellated lead
ore were put into a crucible and ex-
poſed, at firſt, to a gentle, and after-
wards to a ftrong fire: the ore grew
red, and emitted fumes which fiel-
led of fulphur; at length it melted,
and
( 217 )
and the fumes became very copious;
they were accompanied with a yel-
lowiſh flame upon the ſurface of the
melted ore, and when collected had
a whitiſh appearance. The crucible,
after the ore had continued a full
hour in perfect fufion, was taken
from the fire, and when it was cold
it was broken. The mafs which it
contained weighed five ounces and
an half; there was no fcoria obſerv-
able on its furface, nor were any
particles of metal formed; it was
ftill an ore of lead.
The maſs remaining from the laſt
experiment was put into a fresh cru-
cible, and expoſed to a ſtrong melt-
ing heat; the fumes which arofe
from it feemed to be heavy; they
brooded over the furface of the
melted mafs in undulating flames,
which
(218)
which now and then appeared like
burning zinc *. The lead was now
formed, and many particles of it
were fublimed to at leaft fix inches
above the ſurface of the liquid in
the crucible. After letting the cru-
cible continue two hours in this
ftate, I poured out its contents, and
found them confifting partly of lead,
partly of lead ore, and partly of a
very minute portion of browniſh
fcoria. I repeated this experiment
with the fame fucceſs.
Theſe experiments prove, that
ſome ſubſtance or other is contained
in lead ore, which must be difperfed
before the ore can be formed into
lead; and they fhew too, that it re-
quires a confiderable time to effect
the
* It may deſerve to be inquired whether zine
may not be contained in lead, iron, and other
ores, more frequently than is ſuppoſed,
( 219 )
the difperfion of this fubftance, fince
fix ounces of ore, though kept three
hours or more in complete fufion,
were not wholly brought into the
form of lead; they inftruct us alſo to
believe that the lead in this kind of
ore is in its metallic flate, as the ore
was changed into lead without the
addition of any fubftance containing
the inflammable principle; and, laſt-
ly, they render it probable, that the
fumes arising from melted ore, carry
off with them no inconfiderable por-
tion of the lead itſelf. At the great
fmelting houſes in Derbyshire, they
put a ton of ore at a time into the
furnace, and work it off in eight
hours; the ore might be wholly
melted in one hour, but the lead,
perhaps, is not formed in the greateſt
poffible quantity in eight hours.
Some
(2:20)
Some fine teffellated lead ore from
Derbyſhire, was pounded into fmall
lumps, each about the fize of a pea,
and carefully picked from ſpar and
other impurities. Sixteen ounces
of this cre, thus previouſly cleanſed,
were diftilled in an earthen retort;
as foon as the ore felt the fire, the
ftopple of the quilled receiver had a
ftrong finell, refembling that of the
inflammable air, feparable from fome
metals by folution in acids; ſoon af-
ter a ſmall portion of a liquid came
over into the receiver; the fire was
then raiſed till the retort was of a
white heat, when a black matter be-
gan to be fublimed into the neck of
the retort; the operation was then
difcontinued. This experiment was
undertaken with a view of feeing-
whe-
(221)
whether fulphur could be feparated
from lead ore, as it may be from
fome fpecies of the pyrites, by diſtil-
lation, and it appears from the iffue
of the experiment that it cannot, at
leaſt in the degree of heat which is
requifite for fubliming the ore. Up-
on breaking the retort, I found that
the ore had been melted during the
operation, for there was a confiflent
cake of ore of the figure of the bot-
tom of the retort; the weight of this
cake was fifteen ounces and an half,
the weight of the liquid in the re-
ceiver, and of the black matter
which had been fublimed, did not
together amount to one quarter of
an ounce, fo that a quarter of an
ounce or more had been diſperſed,
probably in the form of air, or fome
elaſtic fluid.
The ore by this pro-
cefs
( 222 )
cefs had loft one thirty-fecond part
of its weight. The liquid did not
effervefce with either acids or alka-
lies; nor did it produce any change
in the colour of blue paper, yet I
am certain, from experiment, that
one drop of oil of vitriol, though
diluted with two ounces of water,
would have produced a fenfible red-
nefs on the blue paper which I uſed.
The liquid, notwithstanding, had an
acid taſte, and a pungent fmell, re-
fembling that of the volatile vitriolic
acid.
The black matter which had
been fublimed into the neck of the
retort, was examined with a micro-
ſcope, and it appeared to be pure
lead ore.
The melted ore which
was found at the bottom of the re-
tort, had not any appearance of
ſcoria, or of lead, upon its furface.
Some
(223)
Some phenomena attending this
experiment, deferved, I thought, a
further inveſtigation. I therefore
diftilled another 16 ounces of ore,
but with a fire ftronger and continu-
ed for a longer time, than in the pre-
ceding experiment: the quantity of
liquid was much the fame, there was
a ſmell of fulphur, and, perhaps, to
the amount of half a grain of ful-
phur was found in the receiver; the
ore was in this experiment fublimed
into the neck of the retort to the
thickness of one fourth of an inch.
There was found, as before, a cake
of melted ore at the bottom of the
retort, but no fenfible portion of
either lead or ſcoria*; ſo that we may
fafely
* I have faid no fenfible portion; there
was, however, an appearance of ſcoria ad-
hering to the fide, and an appearance of lead
adhering
(224)
fafely conclude that lead ore cannot
be decompofed by the ftrongest fires
in cloſe veffels, but that it may be
fublimed in them. The ore had loft
near an ounce of its weight.
Though the experiment is fuffici-
ently troublefome, I was not deter-
red from making it once more; for
I wanted to fee whether lead ore
could be wholly fublimed; as I
thought that philofophers might
thereby form fome conjectures of
the efficacy of fubterraneous fires in
fubliming
adhering to the bottom of the retort; but the
quantity of each was exceedingly ſmall, and
they were both, probably, produced from that
minute decompofition of the ore which pro-
duced the fulphur, and which would not, I
think, have taken place in any degree, had
there been no communication with the external
air; but the orifice of the quilled receiver was
not always clofely stopped during the diftilla-
tion.
( 225 )
in lead ores, and, perhaps, ores of
other metallic fubftances. The event
of this third experiment was perfect-
ly correfpondent to that of the two
former, with refpect to the produc-
tion of liquid, and the feparation of
air, which was caught in a bladder,
but was not found to be inflamma-
ble: the lead ore too was ſo plenti-
fully fublimed into the neck of the
retort, that it quite plugged it up
for above three inches in length.
Upon difcontinuing the fire, which
had been raiſed to a degree of heat
exceedingly great, I found the retort
was cracked, and that the cake at
its bottom was very different from
what was found at the bottom of the
other retorts, which had ftood the
fire without cracking; for this cake.
was covered with a black glaffy ſco-
VOL. III.
P
ria
(226)
I
ria of an inch in thickneſs, and the
4
ore which laid under it, was in part
changed into lead, and the whole of
the ore did not weigh quite ten
ounces, fo that above 6 ounces had
been loft by eſcaping through the
crack. By a communication with
the air through the crack, the ore
was decompofed, and thus both lead
and ſcoria were formed, which in the
other experiments, for want of fuch
a decompofition, could not be form-
ed. There was a thin coat of ful-
phur alfo which lined the infide of
the receiver, and this fulphur, pro-
bably, arofe from the decompofition
of the ore, fince none, or next to
none, was obferved in the other dif-
tillations of the ore. I found that
the weight of a cubic foot of the
ore, which had been fublimed into
4
the
( 227 )
the neck of the retort, was 7500
Qunces; which fufficiently agrees
with the weight I had before afcer-
tained of this kind of ore. A cubic
foot of the black glaffy fcoria weigh-
ed 3333 ounces; and the metallic
cake which laid under it, and which
confifted partly of lead, and princi-
pally of ore not quite changed into
lead, gave 8738 ounces to the cubic
foot.
Finding that fulphur could not be
ſeparated from lead ore by diftilling
it in clofe veffels without addition,
and yet being much difpofed to
think that it contained a confidera-
ble portion of fulphur, I first thought
of diftilling it with charcoal duft,
iron filings, fand, and other addi-
tions; but recollecting that fulphur
might be feparated from antimony
P.2
by
(228)
by folution in acids, I thought it
not improbable, that it might be ſe-
parated from lead ore by the fame
means, and the fuccefs of the follow-
ing experiment abundantly juftified
the conjecture.
Upon ten ounces of lead ore,
cleanfed as in the preceding experi-
ments, I poured five ounces of the
ſtrongeſt fuming fpirits of nitre; this
ftrong acid not ſeeming to act upon
the ore, I diluted it with five ounces
of water; a violent ebullition, ac-
companied with red fumes, immedi-
ately took place; the folution of the
ore in this menftruum became mani-
feft, and when it was finished, there
remained floating upon the furface
of the menftruum a cake of fine yel-
low fulphur, perfectly refembling
common fulphur.
:
1 re-
( 229 )
I repeated this experiment a great
many times, in order to aſcertain the
quantity of fulphur contained in lead
ore, and ſeparable therefrom by ſo-
lution in acid of nitre. The refults
of different experiments were feldom
the fame; the matter ſeparable from
the ore by folution, after being re-
peatedly waſhed in large quantities
of hot water, in order to free it from
every faline admixture, fometimes
amounted to more, fometimes to
leſs than one-third of the weight of
the ore. This matter may, for the
fake of diſtinction, be called crude
fulphur. Its apparent purity might
induce a belief that it contained no
heterogeneous mixture, yet the fol-
lowing experiments fhew how much
we ſhould be deceived in forming
fuch
P 3
(230)
1
fuch a conjecture and how rightly
it is denominated crude fulphur.
From one hundred and twenty
parts, by weight, of lead ore, I ob-
tained, by folution in acid of nitre,
fubfequent waſhing in hot water, and
drying by a gentle fire, forty parts
of a fubftance which looked like ful-
phur thefe forty parts were put on
a red-hot iron, the fulphur was made
manifeſt by a blue flame and pun-
gent fmell. When the flame went
out, there remained upon the iron
unconſumed, twenty-fix parts of a
greyish calx; the weight of the ful-
phur which was confumed muft there-
fore have amounted to fourteen parts,
or between one eighth and one ninth
part of the weight of the ore. It
has been obferved, that the weight
of the matter, feparable from lead ore
by:
(231
( 231 )
by folution in acid of nitre, ſome-
times exceeded and fometimes fell
fhort of, one third part of the weight
of the ore; this variety, as far as I
have been able to obſerve, does not
extend to the quantity of fulphur
contained in a given quantity of ore,
it depends upon the quantity of calx
remaining after the burning of the
fulphur. Different lead ores will
doubtless contain different quantities
of fulphur; but that the fulphur
contained in the lead ore which I
examined, conftitutes between one
eighth and one ninth part of the
weight of the ore, is a conclufion
upon which, from a variety of expe-
riments, I am difpofed to rely.
There are faid to be annually ſmelted
in Derbyshire about ten thoufand tons
P 4
of
( 232 )
of lead ore*; now if means could be
invented (which I think very poffi-
ble) of faving the fulphur contained
in ten thousand tons of ore, fuppof-
ing that the ore fhould only yield
one tenth of its weight of fulphur,
though it unquestionably contains
more, Derbyshire alone would furnish
annually one thoufand tons of ful-
phur, the value of which would an-
nually be about fifreen thouſand
pounds. I mention this circumſtance
thus publicly, in hopes that the lead
fmelters may be induced to proſe-
cute the fubject. If the fulphur
contained in the lead ore could be
collected, it would not only be a lu-
crative bufinefs to the fmelters, but
a great faving to the nation. We at
prefent
* This eſtimate is, I have reafon to think,
too high.
( 233 )
prefent import the fulphur we ufe,
and the confumption of this com-
modity is exceeding great, in the
making of gunpowder, in form-
ing the mixture for covering the
bottom and fides of ſhips, and
in a great variety of arts. The
fimelters need not be apprehenſive
left the quality of the ore fhould be
injured by extracting the fulphur.
Eighteen hundred weight of ore,
from which the fulphur has been
extracted, will certainly yield as
much lead as twenty hundred weight
of ore, from which the fulphur has
not been extracted, and it will, pro-
bably, yield more. Arfenic is ex-
tracted
*This mixture is made of one part of tal-
low, of one part of brimstone, and of three
parts nearly of rofin. The tallow and rofin
are melted together, and the brimstone is
ftirred into them; 140 pounds of brimſtone is
enough for a veffel of 140 tons.
(234)
tracted from a particular ore in
Saxony, by roafting the ore in a fur-
nace, which has a long horizontal
chimney; the chimney is large, has
many windings and angles, that the
arfenical vapour which arifes from
the ore may be the more eafily con-
denfed: the arfenic attaches itſelf
like foot to the chimney, and is from
time to time ſwept out. It is very
probable, that by fome fuch con-
trivance the fulphur contained in
lead ore might be collected. The
fmelters call every thing fulphur
which is volatilized during the roaft-
ing or fluxing of an ore; but none
of thoſe with whom I have converſed,
had any notion that common ful-
phur could be feparated from lead
ore.
The greyish calx which remained
upon
(235)
upon the iron after the fulphur was
confumed, was put upon a piece of
lighted charcoal; the heat of the
charcoal being quickened by blow-
ing upon it, a great number of glo-
bules of lead were formed upon its
furface. From hence it appears,
that this calx is not an unmetallic
earth contained in the ore, which
the acid of nitre could not diffolve;.
but a calx of lead, probably pro-
duced by the violent action of the
acid, and which, by the addition of
phlogiſton, may be exhibited in its
metallic form. The quantity of this
calx depends much upon the action.
of the acid upon the ore; if that
action is violent, the calx is in
greater abundance than if it be mo-
derate; and I am not certain whe-
ther the experiment might not be fo
managed,
( 236 )
managed, that there would be little
or no calx remaining; that is, a
given quantity of ore might be fo
diffolved in the acid of nitre, that
nothing would remain undiffolved
except the fulphur. But I have not
yet perfectly fatisfied myſelf as to
the conſtituent parts of lead ore. I
am certain that it contains lead, and
fulphur, a liquid, and air: of the ex-
iftence of the three firft there can be
no doubt, from what has been ſaid,
and the air is rendered beautifully
apparent by the following experi-
ment.
Let fome lead ore be reduced into
a fine powder, put it into a narrow-
bottomed ale glafs, fill the glaſs
three parts with water, drop into the
water a portion of the ftrong acid of
nitre, you may judge of the requi-
fite
( 237 )
fite quantity by feeing the folution
commence, and you will obſerve the
ore universally covered with bubbles
of air, thefe will buoy the ore up
in large tufts to the furface, and the
air will continue to be feparated
from the ore till the acid becomes
faturated with the lead. The falt
arifing from the union of the nitrous
acid to the lead often appears cry-
ftallized upon the furface of the
menftruum in this experiment; and
if, when the menftruum is in that
ftate, a little freſh acid be added, the
falt inſtantly cryftallizes and falls
down to the bottom of the glass, the
acid having abforbed the water which
held it in folution. When lead is
diffolved in the manner here men-
tioned, by a very diluted acid of ni-
tre, there is no appearance of ful-
phur
(238)
phur upon the furface of the men-
ftruum, there is found at its bottom
a black matter, which is the fulphur.
But though lead, and fulphur, a
liquid, and air*, are unquestionably
conſtituent parts of lead ore, I do
not take upon me to fay, that they
are the only conftituent parts: it is
well known, that during the fmelt-
ing of lead ore, a third part or more
of its weight is fome how or other
loft, fince from one and twenty hun-
dred weight of ore, they feldom ob-
tain above fourteen hundred weight
of lead. What is loft partly conſiſts
of a ſcoria which floats upon the
furface of the lead during the opera-
tion of fmelting, and partly of what
is
* I have ſeparated inflammable air from
lead ore, by diffolving it in the acid of fea
falt.
(239)
is fublimed up the chimney and dif
fipated in the air. The ſcoria, I ap-
prehend, would be very little, even
from a ton of ore, if the ore was
quite free from ſpar: it is the ſpar
which is mixed with the ore that con-
ſtitutes the main portion of the fco-
ria*. I have in my poffeffion a folid
maſs of ſcoria, which accidentally
flowed out from a ſmelting furnace,
and which in colour and conſiſtency
perfectly reſembles grey lime-ftone;
it receives a poliſh as fine as marble,
and it might perhaps with advan-
tage be caſt into moulds for paving
ftones, chimney pieces, and other
mat-
* The fpar without queſtion augiments the
quantity of the fcoria, yet the lead ore, which
appears to the eye to be quite free from fpar,
yields a confiderable portion of a black glaſſy
fcoria, when urged with a fufficient fire.
(240)
matters. It arifes from the fpar mix-
ed with the ore, and, by the addition
of cubical ſpar to the ore during its
fufion, its quantity might be increaf-
ed at no great expence, in any pro-
portion. That part of the ore which
is fublimed and diſperſed in the air,
confifts partly of the fulphur which is
decompofed, and partly of lead; this
fublimed lead attaches itfelf in part
to the fides of the chimney of the
fmelting furnace; the reſt of it flies
up into the air, from whence it falls
upon the ground, poifoning the wa-
ter and herbage upon which it ſet-
tles. This fublimed lead might be
collected either by making it meet
with water, or with the vapour of
water, during its afcent, or by mak-
ing it pass through an horizontal
chimney of a fufficient length.
It
( 241 )
It is not eaſy to determine with
preciſion the quantity of this fublim-
ed lead; a general guefs, however,
may throw fome light upon the fub-
ject. They ufually at a fmelting
houſe work off three tons, or fixty
hundred weight, of lead ore every
twenty-four hours; the fulphur con-
tained in fixty hundred weight of ore,
we will ſuppoſe to be ſeven hundred
weight, and the lead to be forty
hundred weight; the air, liquid, fco-
ria, and fublimed lead muſt toge-
ther, upon this fuppofition, amount
to thirteen hundred weight; now,
admitting three hundred weight of
the thirteen to be fublimed lead, it is
evident that, could it be collected,
there would be an annual faving at
each fmelting houfe of above fifty
tons, which, fuppofing it to be
FOL. III.
е
worth
( 242 )
worth four pounds per ton, would
amount to above two hundred pounds
a year. The price, if not the quan-
tity of lead ſublimate, here affumed,
is, probably, below the truth; but
my end is anſwered in giving this
hint to perfons engaged in the fmelt-
ing buſineſs.
:
The
following
experiments,
though upon a different fubject,
may not be unacceptable to the lovers
of chemiſtry, as I do not remember
to have any where met with them.
It is commonly known, that the
furface of melted lead becomes co-
vered with a pellicle of various co-
lours. I undertook fome experi-
ments in the courſe of laſt winter,
with a view to aſcertain the order in
which the colours fucceeded each
other. The lead which lines the
boxes
( 243 )
boxes in which tea is imported from
China happening to be at hand, fome
of it was melted in an iron ladle; but
I was much furpriſed to find that
its furface, though it was prefently
covered with a dufky pellicle, did
not exhibit any colours. Imagining
that the heat was not fufficiently
ftrong to render the colours vifible,
the fire was urged till the ladle be-
came red hot, the calcined pellicle
upon the furface of the lead was red
hot alfo, but it was ftill without co-
lour. The fame parcel of lead was
boiled in a crucible for a confider-
able time; during the boiling a co-
pious fteam was difcharged, and the
furface of the lead, as is ufual, be-
came covered with a half vitrified
fcoria. The lead which remained un-
vitrified was then examined, and it
Q 2
had
( 244 )
(244
had acquired the property of form-
ing a fucceffion of coloured pellicles,
during the whole time of continuing
in a ſtate of fufion.
Another portion of the fame kind
of lead was expofed to a ftrong cal-
cining heat for a long time; the part
which remained uncalcined did, at
length, acquire the property of ex-
hibiting colours fufficiently vivid.
Theſe experiments induced me to
conclude, that the Chineſe lead was
mixed with ſome ſubſtance from
which it was neceffary to free it ei-
ther by fublimation or calcination,
before it would exhibit its colours.
It would be uſeleſs to mention all
the experiments which I made be-
fore I diſcovered the heterogeneous
ſubſtance with which I fuppofed the
Chineſe lead was mixed. At laft I
hit
(245)
hit upon one which feems fully fuf-
ficient to explain the phenomenon.
Into a ladle full of melted Derby-
fhire lead, which manifefted a fuc-
ceffion of the most vivid colours,
I put a fmall portion of tin, and ob-
ſerved, that as foon as the tin was
melted, and mixed with the lead, no
more colours were to be ſeen. I
do not know precifely the fmalleſt
poffible quantity of tin, which will
be fufficient to deprive a given quan-
tity of lead of its property of form-
ing coloured pellicles, but I have
reaſon to believe that it does not ex-
ceed one five thoufandth part of the
weight of the lead.
Derbyshire lead, which has loft
its property of exhibiting colours by
being mixed with tin, acquires it
again, as is mentioned of the Chineſe
lead,
ез
(246)
lead, by being expoſed to a calcining
heat for a fufficient time; the tin, it
is fuppofed, being feparated from the
lead by calcination, before all the
lead is reduced to a calx.
Some calcined Chineſe lead was
reduced to its metallic form by burn-
ing fome tallow over it. The re-
duced lead gave, when melted, co-
loured pellicles; the calx of tin,
which we ſuppoſe to have been mix-
ed with the calcined lead, not being
ſo eaſily reducible as that of lead.
I find that zinc is another metallic
fubftance which has the fame pro-
perty as tin with refpect to the de-
priving lead of its power of forming
coloured pellicles; but it does not,
I think, poffefs this power in fo emi-
nent a degree as tin. I put finall
portions of bifmuth alfo into melted
lead,
( 247 )
lead, but the lead ftill retained its
quality of forming colours. I melted
together fome filver and lead, but
the lead did not thereby lofe its
power of forming colours. A little
tin added to a mixture of lead and
bifinuth, or to a mixture of filver
and lead, immediately takes away
from the reſpective mixtures the fa-
culty of forming coloured pellicles.
This quality of tin has hitherto,
as far as I know, been unobferved;
but every new fact, relative to the
actions of bodies one upon another,
ought to be recorded. The change,
produced in lead by the admixture
of a ſmall portion of tin, is much felt
by the plumbers, as it makes the
metal fo hard and harsh, that it is
not without difficulty they can caft
it into fheet lead. If their old lead
Q4
does
( 248 )
does not work fo willingly, nor
exhibit colours fo readily, as new
lead, they may refer the difference
to the fmall quantity of tin contained
in the folder, from which old lead
can feldom be thoroughly freed.
With reſpect to the order in which
the colours fucceed one another upon
the furface of melted lead, it feems
to be the following one; yellow, pur-
ple, blue,-yellow, purple, green,—
pink, green, pink, green. Upon ex-
hibiting the bright furface of melted
lead to the air, I have often obferv-
ed theſe ten changes to follow one
another in a more or lefs rapid fuc-
ceffion, according to the degree of
heat prevailing in the lead. If the
heat is but ſmall, the fucceffion ſtops
before it has gone through all the
changes; but with the greateſt heat
I did
( 249 )
I did not obſerve any further varia-
tion. All the colours are very vivid,
and each ſeems to go through all the
ſhades belonging to it before it is
changed into the next in order.
The formation of theſe colours
may be explained from what has
been advanced by Sir Ifaac Newton,
and illuftrated by the very ingeni-
ous experiments of Mr. Delaval, re-
lative to the fize of the particles con-
ftituting coloured bodies.
ESSAY
ESSAY VIII.
OF THE
SMELTING OF LEAD ORE,
AS PRACTISED IN DERBYSHIRE.
T
HERE is a certain ftandard
of perfection in the exerciſe of
every art, which is not always well
underſtood; and after men do fuffi-
ciently comprehend it, many ages
often pafs away before they are for-
tunate or ingenious enough to attain
it. To extract the greateft poffible
quantity
( 252 )
quantity of metal, from any parti-
cular kind, and any definite quantity
of ore, is a problem of great impor-
tance, whether it be confidered in a
philofophical or a commercial light;
yet he who ſhould apply himſelf to
the folution of it, with an expecta.
tion of being uſeful to mankind,
must take into confideration another
circumftance, of as much importance
as the quantity of metal to be ex-
tracted, the expence attending the
proceſs. For it is obvious, that a
great quantity of metal extracted at
a great expence, may not produce fo
much clear profit, as a lefs quantity
procured at an eafier rate; there is a
beneficial limit between the quantity
to be obtained, and the expence at-
tending the operation, which nothing
but experience can aſcertain.
It
( 253 )
It has been proved, by experi-
ments made in France, that lead ore,
when ſmelted by a fire made of wood,
yielded one tenth more lead, than in
the ordinary method of fmelting by
means of pitcoal; yet pitcoal is fo
much cheaper than wood, in Derby-
fhire, and moſt other parts of Great
Britain, that the lofs of a tenth of
the lead is, probably, more than
compenfated, by the ufe of pitcoal
inſtead of wood or charcoal. It is
poffible, perhaps, even with the uſe
of pitcoal, by an alteration in the
procefs of finelting, to extract from
every twenty tons of ore, one ton
more of lead than is any where ex-
tracted at prefent; but whether the
price of one ton of lead, would be
more
*Effais des Mines, par M. Hellot, Vol II.
P. 114.
(254)
more than fufficient to defray the
extraordinary expence attending the
alteration of the proceſs, muſt be
left to the deciſion of thoſe who are
intereſted in the fuccefs of fuch in-
quiries.
The art of finelting the ores of all
metallic fubftances, was, probably,
at first very imperfect in every part
of the world; and this doubtleſs has
been a reaſon, why the ufe of iron
has every where been of a more re-
cent date, than that of the other
metals, fince it requires the applica-
tion of a much ſtronger fire to finelt
the ores of iron, than thoſe of any
other metal.
We have no certain account when,
or by whom, the feveral metals were
difcovered; Wallerius fays, that, as
far as he knew, Pliny was the firſt
2.
who
( 255 )
-
who enumerated the fix metals:*
Pliny may, probably, be the first
Natural Hiftorian who mentioned
them, but they were certainly known
long before the age of Pliny, and
were mentioned both by Homer, and
by an author far more ancient than
Homer-Mofes." Only the gold,
and the filver, the brafs (copper), the
iron, the tin, and the lead, every thing
that may abide the fire, ye fhall make
it go through the fire, and it fhall be
clean." From this teftimony we
are certain that all the metals were
known, at leaſt in the country of the
Midianites, above 1450 years before
the birth of Chrift, or near 900 years
after
*Primus (fcil. Plinius) quantum mihi
conftat, fex metalla enumeravit. Waller. de
Syf. Minera. p. 10.
† Numb. xxxi. 22.
(256)
after the deluge. When I fay all
the metals, I must be underſtood to
mean, all thoſe which were anciently
known; for platina, the feventh me-
tal, has been but recently diſcovered,
and is not yet brought into general
ufe; and quickfilver or mercury is not
admitted by mineralogifts into the
clafs of metals; though it has a good
right to be admitted, fince in a fuffi-
cient degree of cold, it poffeffes the
great characteriſtic property of a
metal, as diftinguifhed from a Semi-
metal — malleability. This property
of malleability, as conftituting the
criterion by which metals differ from
femimetals, is not over rigidly to be
infifted on, fince iron, when firft
fluxed from its ore, or when con-
verted into ſteel, and hardened by
being fuddenly immerfed when red
hot
( 257 )
hot in water, is lefs malleable than
zinc, which is always claffed amongſt
the femimetals.
It has been contended, that copper
was one of the first metals which was
ufed as money, and that gold and
filver were, in very remote ages, of
little account in that view. In many
inftances the greatnefs of the Roman
name has made us forget the æra
when that people began to be dif-
tinguiſhed in hiftory, and induced
us to confider their cuftoms, as the
firſt which prevailed amongſt man-
kind. It is granted, that Servius
Tullius firſt coined copper, and that
the Romans ufed no other currency
till the four hundredth and eighty-
fifth year of their city,* when filver
began to be coined; but from this
* Plin. Hift. Nat. Lib. XXXIII. S. 13.
VOL. III.
R
con-
( 258 )
conceffion, no argument can be de
duced for the fole uſe of copper as a
currency, in the firft ages of the
world. We know, from undoubted
authority, that filver was uſed in
commerce, at leaſt eleven hundred
years before even the foundation of
Rome. And Abraham weighed to
Ephron, the filver which he had named
in the audience of the fons of Heth, four
bundred fhekels of filver, current money
with the merchant*. About 60 years
before Abraham paid this fum for a
piece of land in Canaan, he is faid,
upon his return from Egypt, to have
been rich, not in copper and iron,
but in filver and gold †.
Iron and copper were certainly
known before the deluge; and it is
probable, that all the other metals,
every
* Gen. xxiii. 16.
Gen. xiii. 2.
( 259 )
every one of which is more eafily ex-
tracted from its ore than iron and
copper are from theirs, were known
alfo to the Antediluvians; we have
proof, however, that in the time of
Abraham, gold and filver were ef
teemed, as they are at prefent, pre-
cious metals; and hence it feems
reaſonable enough to conclude, that
Noah was able to inftruct his de-
fcendants in the art of fmelting me-
tallic ores: but, though this be ad-
mitted, we need not be furpriſed at
the ignorance of many barbarous na-
tions in this particular. For the va-
rious colonies which, either by com-
pulfion or choice, quitted the plains
of Afia, in ſearch of ſettlements, may
not always have had in their com-
pany men who had been inftructed in
the art of fmelting; and thofe who
R 2
did
( 260 )
(260
did underſtand it, when the colony
firſt migrated, may, in many in-
ſtances, have died before any ores
were diſcovered, upon which they
might have exerted their ſkill; and
thus the art of fmelting being once
loft, it is eaſy to conceive that many
nations may have remained for ages
without the uſe of metals, or with
the uſe of ſuch only as are found
ready formed in the earth, or are
eafily fluxed from their ores.
The earth in a little time after
the deluge, and long before it could
have been peopled by the pofterity
of Noah, muſt have become covered
with wood; the moft obvious me-
thod of clearing a country of its
wood, is the fetting it on fire: now
in moſt mineral countries there are
veins of metallic ores, which lie
con-
(261)
contiguous to the furface of the
earth, and theſe having been fluxed
whilft the woods growing over them
were on fire, probably, fuggefted to
many nations the firft idea of ſmelt-
ing ores.
Pow'rful gold firſt raiſed his head,
And brafs, and filver, and ignoble lead.
When fhady woods, on lofty mountains grown,
Felt fcorching fires; whether from thunder
thrown,
Or elfe by man's defign the flames arofé.
Whatever 'twas that gave theſe flames their
birth,
Which burnt the towering trees and ſcorch'd
the earth,
Hot ſtreams of filver, gold, and lead, and braſs,
(copper)
As nature gave a hollow proper place,
Defcended down, and form'd a glittring
mafs *
R 3
There
Lucretius by Creech, Vol. II. p. 572.
( 262 )
There is no natural abfurdity in
this notion of the poet; and indeed
it is confirmed by the teftimony of
various ancient hiftorians, who ſpeak
of filver and other metals being
melted out of the earth, during the
burning of the woods upon the Alps
and the Pyrenees. A fimilar circum-
ftance is faid to have happened in
Croatia in the year 1761; a large
maſs of a mixed metal, compoſed of
copper, iron, tin and filver, having
been fluxed, during the conflagra-
tion of a wood, which was acciden-
tally ſet on fire.*
The putting a quantity of ore up-
on a heap of wood, and fetting the
pile on fire, in conformity to the
manner in which ores were melted
during the burning of forefts, was,
Annual Regiſter, 1761, p. 138.
it
(263)
it may be conjectured, the firſt rude
proceſs by which metals were ex-
tracted from their ores. But as the
force of fire is greatly diminiſhed,
when the flame is fuffered to expand
itſelf, and as the air acts more forci-
bly in exciting fire, when it ruſhes
upon it with greater velocity, it is
likely, that the heap of wood and
ore would foon be furrounded with
a wall of ftone, in which fufficient
openings would be left for the en-
trance of the air, and thus a kind of
furnace would be conftructed.
Peruvians, we are told, "had diſcover-
ed the art of finelting and refining
filver, either by the fimple applica-
tion of fire, or where the ore was
more ftubborn and impregnated with
foreign fubftances, by placing it in
fmall ovens or furnaces on high
grounds,
R 4
The
(264)
grounds, fo artificially conftructed
that the draught of air performed
the function of a bellows, a machine
with which they were totally unac-
quainted."
This method of ſmelting ores on
high grounds, without the affiftance
of a bellows, at leaſt of a bellows
moved by water, feems to have been
formerly practiſed in other countries
as well as in Peru. When M. Belon
travelled into Greece, he found the
furnaces placed on the fides of ri-
vulets, and obferves, that all their
bellows played with wheels turned
by ſtreams of water, yet formerly
they had ſmelted their ores in a dif-
ferent manner: for upon the moun-
tains
**Robertfon's Hift. of America.-Alonfo
Barba, Treatife of Metals, French Tranflation,
Vol. I. p. 272.
(265)
tains of Macedonia, where mines had
been wrought in the time of Philip
the father of Alexander, great heaps
of flag have been diſcovered, which
are fituated ſo far above any river of
the country, that the furnaces from
which they were formed, muft, pro-
bably, have been wrought by the
wind. There are feveral places in
Derbyshire called Boles by the inha-
bitants, where lead has been ancient-
ly fmelted, before the invention of
moving bellows by water. Theſe
places are diſcovered by the flags of
lead, which are found near them;
there is no certain tradition concern-
ing the manner in which the ore
was ſmelted at theſe boles, it was,
probably, as fimple as that of the
Peruvians; for in Derbyshire, as well
as in Peru, they feem chiefly to have
relied
(266)
relied upon the ftrength of the wind
for the fuccefs of the operation; the
boles being always fituated upon high
grounds, and moftly upon that fide
of a hill, which faces the weft. This
fituation was not fixed upon with-
out defign, fince the wind blows in
England, in the courfe of a year,
near twice as many days from that
quarter as from any other. A me-
thod is mentioned by Erckern † of
fmelting bifmuth ore by the wind,
and it ſeems as if the ore of lead
might have been fmelted at theſe
boles,
* As may appear from the following
abridged ſtate of the winds at London in the
years 1774 and 1
N
177425
1775.
S E W INWI SE NE SW
I
Idys
2 I I 17212 24 432 30 74 126 dys
1775222111 1839 3272148
Philof. Tranf. 1774-5.
P. 305.
z
See Fleta Minor, by Sir John Pettus,
( 267 )
boles, after the fame manner. This
method confifts in putting the bif-
muth ore, when beat to a proper
fize, into ſmall flat iron pans, theſe
are fet in a row contiguous to each
other, in an open place, and when
there is a strong wind, a fire of dry
wood is made clofe to the pans, and
on that fide of them from which the
wind blows; by this contrivance, the
wind driving down the flame of the
wood upon the pans, the ore con-
tained in them is quickly melted.
A pig of lead was dug up at one of
the boles in the year 1766 on Crom-
ford moor near Matlock; upon its un-
der furface there is an infcription in
relievo, from which it appears to
have been ſmelted in the age of the
Emperor Adrian; it is not very dif-
ferent in ſhape from the pigs which
3:
are
( 268 )
are caft at prefent; it confifts of fe
veral horizontal layers of unequal
thickneffes, and there is an irregular
hole in it running from the top to
near the middle of its fubftance;
from theſe appearances it feems as if
it had been formed by pouring into
a mould, at different times, feveral
quantities of lead; and if lead had
been fmelted after the manner before
mentioned of fmelting bifmuth ore,
the feveral pans being emptied, at
different times as they became ready,
into the fame mould, would have
yielded a maſs of lead divided into
layers of unequal thickneffes, and
reſembling this Roman pig; for the
hole in its furface was, probably,
made accidentally, from the unequal
cooling of the lead, or from fome
extraneous matter being lodged in it.
The
(269)
The boles in Derbyshire are, pro-
bably, many of them of high anti-
quity, as appears from the pig of
lead before mentioned; yet I have
met with a paffage in a writer of the
laft century, from which it is evident,
that the method of fmelting lead on
high grounds was then practifed in
"The lead-ftones in the
Peak lie but juft within the ground
next to the upper cruft of the earth.
the Peak.
They melt the lead upon the top of
the hills that lie open to the weſt
wind; making their fires to melt it
as foon as the weft wind begins to
blow; which wind by long experi-
ence they find holds longeſt of all
others. But, for what reaſon I know
not, fince I fhould think lead were
the eafieft of all metals to melt,
they
(270)
they make their fires extraordinary
great."*
The fmelting of ore by the varia-
ble and uncertain action of the wind,
muſt have been a troublefome pro-
cefs. It has therefore been univer-
fally difufed, and the more regular
blaft of a bellows has been intro-
duced in its ſtead. The invention of
the bellows is attributed by Strabo to
Anacharfis the Scythian: but it is
more probable, that he was the in-
ventor of fome improvement of this
machine, than of the machine itſelf.;
for Homer, who lived long before the
age
of Anacharfis, defcribes Vulcan as
employing twenty pair of bellows at
once, in the formation of Achilles's
**Childrey's Britan. Bacon. 1661.
Strab. Geog, Lib. VII.
fhield.
(271)
*
hield. It is difficult to fay when
the art of moving bellows, by means
of a water wheel, was firſt diſcovered;
it is pretty certain, that the ancients
did not know it; and that it was
very generally known, amongſt the
Germans at leaft, in the time of
Agricola, one of the first of our
metallurgic writers, for he fpeaks of
it in feveral places without any hint
of its being a recent invention.
The heat of the fire in a furnace de-
pending much upon the force of the
blaſt of air impelled againſt the fuel;
and that force, other circumftances
remaining the fame, being in pro-
portion to the quantity and velocity
of the air; the application of a power
able
* Iliad. Lib. XVIII. v. 470.
Agric. de Re Metal. publiſhed in 1550,
P. 165. 338.
(~272)
able fuddenly to comprefs the largest
bellows when fwelled with air, could
not fail of being confidered by me-
tallurgifts, as an invention, whenever
it was made, of the laft importance.
The moderns accordingly have, in
many inftances, worked over again,
with confiderable profit, the heaps of
iron and other kinds of flag, from
which the metal had been but im-
perfectly extracted, before the mov-
ing of bellows by water was difco-
vered.
It is not fifty years fince the blast
or hearth furnace, was the only one
in uſe for ſmelting lead cre in Der-
byshire. In this furnace ore and
charcoal, or ore and what they call
white coal, which is wood dried but
not charred, being placed in alter-
nate layers, upon a hearth properly
con-
( 273 )
}
conftructed, the fire is raiſed by the
blast of a bellows, moved by a
water wheel; the ore is foon ſmelt-
ed by the violence of the fire, and
the lead as it is produced trickles
down a proper channel, into a place
contrived for its reception. There
are not at prefent, I believe, above
one or two of theſe ore hearths in the
whole county of Derby; this kind
of furnace, however, is not likely
to go entirely out of ufe, fince it is
frequently applied to the extracting
lead from the flag which is produc-
ed, either at the ore hearth, or the
cupola furnace, and it is then called
a flag hearth; and the lead thus ob-
tained is called flag lead: the fire in
a flag hearth is made of the cinder of
pitcoal inftead of charcoal.
The furnace called a cupol or cu
VOL. III.
S
pota,
( 274 )
pola, in which ores are fmelted by
the flame of pitcoal, is faid to have
been invented about the year 1698,
by a phyfician named Wright*,
though Beccher may, perhaps, be
thought to have a prior claim to its
invention or introduction from Ger-
manyt. But whoever was the firſt
inventor of the cupola, it is now in
general ufe, not only in Derbyſhire
and other counties, for the fmelting
of the ores of lead, but both at home
and abroad, where it is called the
English furnace, for the fmelting of
copper ores. This furnace is fo
contrived, that the ore is melted, not
by coming into immediate contact
with the fuel, but by the reverbe-
ration of the flame upon it. The
bottom of the furnace on which the
* Effais des Mines, Vol. II. p. 114.
† Sée Vol. I. p. 33•
lead
(275)
-
Head ore is placed, is fomewhat con-
cave, fhelving from the fides towards
the middle; its roof is low and arch-
ed, refembling the roof of a baker's
oven; the fire is placed at one end
of the furnace, upon an iron grate,
to the bottom of which the air has
free accefs; at the other end oppo-
fite to the fire-place, is a high per-
pendicular chimney; the direction
of the flame, when all the apertures
in the fides of the furnace are cloſed
up, is neceffarily determined, by
the ſtream of air which enters at the
grate, towards the chimney, and in
tending thither it ftrikes upon the
roof of the furnace, and being re-
verberated from thence upon the
ore, it foon melts it.
It is not always an eafy matter to
meet with a current of water fuffi-
S 2
cient
(276)
置
​cient to move the bellows required
in finelting on an hearth furnace;
and to carry the ore from the mine
where it is dug to a confiderable
diftance to be fmelted, is attended
with great expence; this expence is
faved by finelting in the cupola
furnace, which not requiring the
uſe of bellows, may be conftructed
any where. Wood is very fcarce in
every mining county in England;
and though pitcoal cofts ten or
twelve fhillings a ton in Derby-
fhire, yet they can ſmelt a definite
quantity of ore in the cupola, at a
far lefs expence by means of pit-
coal, than of wood. The flame
which plays upon the furface of the
ore and fmelts it in a cupola fur-
nace, is not driven againſt it with
much violence; by this means
fmall
•
!
7
(277)
fall particles of ore, called bel-
land, may be finelted in a cupola
/furnace with great convenience,
which would be driven away, if
་
expoſed to the fierce blaft of a
pair of bellows in a hearth furnace.
-Thefe are fome of the advantages
attending the uſe of a cupola in pre-
ference to a hearth furnace; and to
thefe may be added one fuperior to
all the rest, -the prefervation of
the workmen's lives; the noxious
particles of lead are carried up the
chimney in a cupola, whilft they are
driven in the face of the hearth
fmelter at every blaft of the bellows.
They generally put into the cù-
pola furnace a ton of ore, previouſly
beat ſmall and properly dreffed,, at
one time; this quantity they call a
charge; if the ore is very poor in lead,
they put in fomewhat more, and they
work
$ 3
(278)
work off three charges of ore in
every twenty-four hours. In about
fix hours from the time of charg--
ing the ore becomes as fluid as
milk. Before the ore becomes fluid,
and even whilft it continues in à
ſtate of fufion, a confiderable por-
tion of its weight is carried off
through the chimney; what remains
in the furnace confifts of two dif
ferent fubftances,-of the lead, for
the obtaining of which the process,
was commenced, and of the flag
or ſcoria. The proportion between
thefe parts is
is not always the
fame, even in the fame kind of
ore; it depending much upon the
management of the fire. The lead,
being heavier than the flag, finks
through it as it is formed, and fet-
tles into the concavity of the bot-
tom of the furnace. The pure flag,.
accord-
( 279 )
1
according to the idea here given, is
that part of the ore of lead which is
neither driven off by the heat of the
furnace, nor changed into lead. In
order to obtain the lead free from
the flag which ſwims over it, the
finelters uſually throw in about a
bufhel of lime; not, as is ufually
fuppofed, in order to contribute to-
wards the more perfect fufion of the
ore, but to dry up the flag which
floats upon the furface of the lead,
and which, being as liquid as lead,
might otherwife flow out along
with it. The flag being thus thick-
ened by an admixture of lime, is
raked up towards the fides of the
furnace, and the lead is left at the
bottom. There is a hole in one of the
fides of the furnace, which is pro-
perly stopped during the finelting
$ 4
of
( 280 )
}
of the ore; when the flag is raked
off, this hole is opened, and being
fituated lower than the lead in the
furnace, the lead gufhes through it
into an iron pot placed contiguous
to the fide of the furnace; from this
por
it is laded into iron moulds, each
containing what they call a pig of
lead; the pigs, when cold, being or-
dinarily ftamped with the maker's
name, are fold under the name of org
lead. After the lead has all flowed
out of the furnace, they ftop up the
tap hole, and drawing down the
flag and lime into the middle of the
furnace, they raiſe the fire till the
mixture of flag and lime, which
they fimply term flag, is rendered
very liquid; upon this liquid mafs,
they throw another quantity of
Time to dry it up as in the former
i
part
(281)
--
7.
part of the procefs. This fecond
mixture of flag and lime is then
raked out of the furnace, and the
fmall portion of lead feparated from
the fufion of the firft, generally to
the amount of twenty or thirty
pounds, being let out of the fur-
nace, a new charge of ore is put in,
and the operation re-commenced.
In order to ſpare the lime, and the
expence of fuel attending the flux-
ing of the mixture of lime and flag,
they have in fome furnaces lately
contrived a hole, through which
they fuffer the main part of the li-
quid flag to flow out, before they
tap the furnace for the lead; upon
the little remaining flag they throw
a fmall portion of lime, and draw
the mixture out of the furnace.
without fmelting it. This kind of
fur-
(282)
furnace they have nick-named a
Maccaroni.
The proceſs of fmelting here de-
fcribed, appears to be defective in
fome points, which I will take the
liberty to mention, and at the fame
time ſuggeſt the means of improve-
ment; without, however, prefuming
to fay, how far it may be expedient
to adopt the propofed alterations;
being fenfible that what may appear
very feaſible in theory, or may even
anſwer in ſmall affays, may not be
practicable in large works.
The first alteration which I would
propofe to the confideration of the
lead fmelters, is to fubftitute an ho
rizontal chimney of two or three
hundred yards in length, in the
place of the perpendicular one now
in uſe. In the preceding Effay,
which
(283)
which was firſt publiſhed in 1778,
mention is made of the probability
of faving a large quantity of fub-
limed lead, by making the fmoke
which rifes from the ore paſs
through an horizontal chimney,
with various windings to condenfe
the vapour. I have fince converfed
with fome of the principal lead
fimelters in Derbyshire, and find that
I had over-rated the quantity of this
fublimed lead; the weight of the
fcoria from a ton of ore, amounting.
to more than I had fuppofed; they
were all of them, however, of opi-
nion, that the plan I had propoſed
for faving the fublimate, was a very
rational one. But fo difficult is it
to wean artifts from their ancient
ways of operating, that I queftion
very much. whether any of them
3.
would
( 284 )
would ever have adopted the plan⠀
they approved, if an horizontal
chimney, which was built a little
time ago in Middleton dale, for a
quite different purpofe, had not
given them a full proof of the
practicability of faving the fubli-
mate of lead, which is loft in the
ordinary method of fmelting. This
chimney was built on the fide of an
hill to prevent fome adjoining paf-
tures from being injured by the
fmoke of the furnace. It not only
anfwers that end, but it is found
alfo to collect confiderable quanti-
ties of the lead, which is fublimed:
during the fmelting of the ore;
this fublimed lead is of a whitifh.
caft, and is fold to the painters at
ten or twelve pounds a ton; it
might perhaps be converted into red
lead with ftill more profit.
A fe
!
285)
A fecond circumftance to be at-
tended to in the fmelting of lead ore,
is the faving the fulphur contained in
it. The pure lead ore of Derbyshire
contains between an eighth and a
ninth part of its weight of fulphur;
but as the ore which is fmelted is
never pure, being mixed with par-
ticles of Spar, cawk, limeſtone, brazil,
and other ſubſtances, which the mi-
ners cáli deads, we fhall be high
enough in our fuppofition, if we fay
that the ordinary ore contains a tenth
of its weight of fulphur; it may not,
probably, contain fo much, but
even a twelfth part, could it be col-
lected at a ſmall expence, would be
an object of great importance to the'
finelter. In the common method of
fmelting lead ore there is no ap-
pearance of the fulphur it contains,
it
(286)
it is confumed by the flame of the
furnace, as foon as it is feparated
from the ore; an attentive obſerver
may, indeed, by looking into the
furnace, diftinguifh a diverfity in the
colour of the flame, at different pe-
riods of the procefs; during the first
three or four hours after the ore is
put into the furnace, the flame has
a bluish tint, proceeding no doubt
from the fulphur which, in being
fublimed from the ore, is inflamed:
after all the fulphur is feparated
from the ore, the flame has a whit-
ifh caft, and then, and not before,
the fire may be raiſed for finiſhing
the operation; for if the fire be made
ftrong before the fulphur be difperf
ed, the quantity of lead is lefs, pro-
bably, for two reafons; the fulphur
unites itſelf in part to the lead which
is
(287)
>
is formed, and by this union be-
comes infeparable from it; for the
fulphur cannot without much diffi-
culty be feparated from an artificial
mixture of lead and fulphur, when
the two ingredients have been fufed
· together. -2. The fulphur, whilſt
it continues united to the lead in
the natural ore, renders the ore vo-
latile, fo that in a ſtrong heat a great
portion of it is driven off. Hence,
very fulphureous ores fhould be
roaſted for a long time with a gen-
tle heat, and in this proper manage-
ment of the fire, principally conſiſts
the fuperiority of one fielter above
another.
An old lead fmelter informed me
that he had often reduced a ton of
ore to 16 hundred weight by roaft-
ing it, but that he did not obtain
more
T288
288)
!
more metal from it by a fubfequent
fufion, than if he had fluxed it with-
out a previous roafting. This may
be true of fome forts of ore, but it
is not true of very fulphureous ores.
Indeed the fire may be fo regulated
in a cupola furnace, as to make it
anfwer the purpoſe of a roafting and
a fmelting furnace at the fame time.
I have feen much lead loft by fielt-
ing a ton of fulphureous ore in eight
hours, which might have been faved,
if the fire had at firft been kept fo
gentle as to have allowed twelve
hours for finiſhing the operation.
Sulphur cannot be feparated from
lead ore in clofe veffels, and the lead
ore melts with fo fmall a degree of
heat, that there may be more diffi-
culty in procuring the fulphur from
the ores of lead, than from thofe of
"
copper
(289)
copper or iron, however, I am far
from thinking the matter impracti
cable, though I have not yet hit up-
on the method of doing it; and the
following reflections may, perhaps,
tend to fuperfede the neceffity of
collecting the fulphur in fubftance.
When it is faid that the fulphur is
confumed by the flame of the fur-
nace as foon as it is feparated from
the ore, the reader will pleafe to re-
collect, that fulphur confifts of two
parts, of an inflammable part,
by which it is rendered combustible,
and of an acid part, which is fet
at liberty, in the form of vapour,
during the burning of the fulphur.
Now this acid, though it may be
driven out of the furnace in the
form of a vapour, yet it is incapable
of being thereby decompofed; it fill
VOL. III.
T
con-
( (290
290 )
continues to be an acid; and, could
the vapour be condenſed, might an-
fwer all the fame purpoſes as the
acid of vitriol; fince all the acid of
vitriol, now uſed in commerce, is
actually procured from the burning
of fulphur. That the fact, with
reſpect to the acid not being decom-
pofed, is as I have ſtated it, may be
readily proved. The fmoke which
iffues out of the chimney for fome
hours after each fresh charge of ore,
has a fuffocating fmell, perfectly re-
fembling the ſmell of burning brim-
ftone; and if a wet cloth, or a wet
hand, be held in it for a very ſhort
fpace of time, and afterwards appli-
ed to the tongue, a ftrong acid will
be fenfibly perceived. Various me-
thods may be invented for condenf-
ing this acid vapour, and, probably,
more
( 291 )
more commodious than the follow-
ing one, which, however, I will juſt
take the liberty of mentioning, as,
if it fhould not fucceed, the trial will
be attended with very little expence.
Suppofing then an horizontal
chimney to be built, let the end far-
theft from the fire be turned up by
a tube of earthen ware, or otherwife,
fo that the fulphureous acid may
iſſue out in a direction parallel to the
flue of the chimney, and at the dif
tance of about a foot and an half
above it. Let a number of large
globular veffels be made of either
glafs or lead, each of theſe globes
muſt have two necks fo as to be
capable of being inferted into one
another; let thefe veffels be placed
on the flue of the chimney, the
neck of the firft being inferted into
T 2
the
$
(292)
the tube through which we have
ſuppoſed the fulphureous acid to
iffue, and the neck of the last being
left open, for fear of injuring the
draught of the furnace. Let each of
thefe globular veffels contain a ſmall
quantity of water, then it is con-
ceived, that the heat of the flue will
raiſe the water into vapour, and that
this watery vapour will be the means
of condenſing the fulphureous acid
vapour, if not wholly, at leaft in
fuch a degree as may render the un-
dertaking profitable. When the ful-
phur is all confumed, the draught
of the furnace may be fuffered to
have its ordinary exit at the end of
the horizontal chimney, by a very
flight contrivance of a moveable
damper. Since the first publication
of the preceding Effay, I have feen
an
( 293 )
an horizontal chimney at the copper
works near Liverpool, where every
thing I had faid concerning the pro-
bability of faving fulphur by roaſt-
ing lead ore, is verified with refpect
to copper ore; and I believe a patent
has been granted to fome individual ·
for this mode of collecting fulphur.
Sulphur might be obtained with
equal facility from the pyrites which
is found amongst coal, and this ap-
plication of the pyrites might, pro-
bably, be more lucrative than the
preſent one-making green vitriol *.
A third circumftance, which re-
quires the utmost care of the lead-
fmelter, is the leaving as little lead
as poſſible in the flag. Near every
fmelting-houſe there are thouſands
of tons of flag, which, when properly
affayed,
T 3
Vol. I. p. 229.
( 294 )
affayed, are found to yield from one
eighth to one tenth of their weight
of lead; though no perfon has yet
diſcovered a method of extracting
fo much from them when ſmelted
in large quantities; and indeed the
fmelters are fo little able to obtain
all the lead contained in them, that
in many places they never attempt
to extract any part of it: in fome
places where they do attempt it, I
have known the proprietor of the
flag allow the ſmelters 20 s. for every
pig of lead they procured of the va-
lue of 38s. befides furnishing them.
with fuel and yet the men employ-
ed in ſuch an unwholefome bufinefs,.
feldom made above 7s. a week of
their labour. This fufion of the
flag of a cupola furnace is made, as
has been mentioned, at a hearth fur-
:
3
nace;
( 295 )
nace; the coal cinder, which they uſe
as fuel, and the flag, are foon melted
by the strong blaft of the bellows
into a black mafs, which, when the
fire is very ſtrong, becomes a perfect
glafs; this black maſs, even in its
moft liquid ftate, is very tenacious,
and hinders many of the particles of
lead from fubfiding, and it being
from time to time removed from the
furnace, a confiderable quantity of
lead is left in it, and thereby loft.
A principal part of the lead con-
tained in the flag of the cupola fur-
nace, is not, I apprehend, in the
form of a metal, but in the form of a
litharge or calcined lead: a portion
of the lead, in being finelted from its
ore, is calcined by the violence of
the fire; this calcined lead is not
only very vitrifiable of itfelf, but it
helps
T 4
(296)
Y
helps to vitrify the fpar which is
mixed with the ore, and thus confti-
tutes the liquid fcoria; might it not
be uſeful to throw a quantity of char-
coal duft upon the liquid fcoria in
the cupola furnace, in order that the
calcined lead might be converted
into lead, by uniting itſelf to the
inflammable principle of the char-
coal? Iron will not unite with
lead, but it readily unites with ful-
phur, and, when added to a mixture
of lead and fulphur, it will abſorb
the fulphur, leaving the lead in its.
metallic form; might it not be uſe-
ful to flux fulphureous lead ores in
conjunction with the fcales or other
refufe pieces of iron, or even with
fome forts of iron ore? The
fmelter's great care fhould be to ex-
tract as much lead as poffible at the
first
(297)
first operation of fmelting the ore,
and to leave the flag as poor as pof-
fible;
but if he ſhould ſtill find either
the flag of the cupola furnace, or
that of the hearth furnace, contain-
ing much lead (as that even of the
hearth furnace certainly does), he
may, perhaps, find it worth his while
to reduce the flag into a powder by
a ſtamping mill, or by laying it in
highways to be ground by the carts,
or by fome other contrivance, and
then he may ſeparate the ftony part
of the flag from the metallic, by
wafhing the whole in water, inafmuch
as the metallic part is far heavier
than the other.
I eſtimated the weights of feveral
pieces of flag, and found them to
differ very much from each other;
this difference is principally to be
at-
( 298)
attributed to the different quantities.
of lead left in them.
Weight of a cubie foot of
Slag from a cupola furnace, where
no lime was uſed
Black flag from a hearth furnace
Another piece
Avoir. oz.-
}
3742
3652
3612
Black flag from another hearth fur-
"}
nace---ftruck fire with fteel
Black glafs flag
-
3378
337
This may not be an improper
place to add a word or two concern-
ing the Derbyshire Toadstone, which
conſtitutes one of the principal ftrata.
in the mining country, and which
is fuppofed to have been in its origin
a flag thrown out by a volcano. It
perfectly reſembles fome of the fpe-
cimens, I have feen, of one of the
forts of the lava of Vefuvius, not only
* See Vol. II. p, 206.
in
( 299 )
in the hardneſs of its texture, and
blackneſs of its colour, but in its
weight; a cubic foot of fome forts
of Derbyshire toadftone weighing
more, and of other lefs than a cubic
foot of the Vefuvian lava, which it
reſembles. The streets of London
have ſome of them been paved, of
late years, with a teadſtone from Scot-
land, of the fame nature as the Der-
byſhire toadſtone; and the streets of
Naples have for many centuries paft
been paved with the lava from Ve-
fuvius which reſembles toadftone.
Neither the Derbyshire toadſtone,
nor that fort of Vefuvian lava which
reſembles it, feem to have experienced
in their formation any great degree
of heat; they are but in a half vitri-
fied ftate the toadftone I have fre-
quently melted in a fmith's forge
into
( 300 )
into a black glafs, and the Vefuvian
lava gives a glaſs of the fame kind.
The air has a manifeft action upon
the Derbyſhire toadſtone, for it not
only waftes away the fpar which is
found in the blebs of fome forts of
toadſtone, but it reduces into a
brownish mould, fit for vegetation,
the moſt hard and compact forts;
the Vefuvian lava is fubject to the
fame change from the operation of
the fame cauſe.
Weight of a cubic foot of
Avoir. oz.
Toadſtone hard and free from blebs
2884
Vefuvian lava refembling toadstone
2865
Iron flag, a greenish glafs
2843
Iron flag, a brownish glafs
Iceland cryſtal-Mr. Cotes
Toadstone, decaying
Another piece
Another piece
2729
2720
2680
2662
}
2558
ESSAY
ESSAY
IX.
OF SILVER EXTRACTED FROM LEAD.
WE
E have no filver mines, pro-
perly ſpeaking, in Great Bri-
tain, but we have plenty of lead,
from which filver is, in fome places,
extracted with much profit, If the
method of doing this had been known
to the ancient Britons, it might have
freed our country from the reproach
of Cicero, who tells his friend Atticus,
that there was not a fcruple of filver
in
(302)
in the whole ifland*; and in another
place, he ſays, that he had heard
there was neither gold nor filver in
Britain. The Romans had a very
imperfect knowledge of this country
in the time of Cicero, fo that his ac-
count of the matter may not, per
haps, deferve to be much relied on;
we are certain, at leaſt, that about
fifty or fixty years afterwards, both
gold and filver were reckoned by
Strabo amongst the products of Bri-
tain ; hence, if the Britons did not
underſtand the art of extracting fil-
ver from lead at the firſt invaſion of
*
the
etiam illud jam cognitum eft, ne-
que argenti fcrupulum effe ullum in illa infula
(Britann.) Epift. ad Att. L. IV. E. XVII.
Epift. Fam. L. VII. E. VII.
L. IV. p. 305,-Sec alfo Tacitus's Life
of Agricola.
( 303 )
the Romans, they foon learned it
from their conquerors; and this be-
comes more probable, if it be ad-
mitted, that filver was coined in Bri-
tain in the time of Auguftus *.
Silver is fo commonly contained in
lead, that it is eſteemed a very great
curiofity to meet with lead which is
intirely free from it: it has even been
afferted, that there is no lead in the
world, except that of Villach in Ca-
rinthia, which does not contain fil-
·ver †.
The more ancient alchemifts, not
knowing, probably, that filver was
fo generally contained in lead, and
* Sir John Pettus Fod Reg.
yet
Il n'y a point de plomb au monde, hot-
mis celui de Villach, que ne contient de l'
argent. Lehman fur les Mines, Vol. I. p.
174.See alfo Philof. Tranf. for 1665, p.
10.
( 304 )
yet obferving that lead, when treated
according to their proceffes, often
gave a portion of filver, were of
opinion, that they could convert lead
into filver. This was an eafy miſtake,
and if they had obtained a portion of
gold, they would, no doubt, have
concluded, that they had tranfmuted
the lead into gold; fince there is no
metal, perhaps, which does not con-
tain a fmall quantity of gold, or from
which gold may not be ſeparated by
long calcination.
Lifter had long ago obferved, that
all the English lead contained filver;
and he ſpeaks as having, by his own
experiments, proved the existence of
filver in the lead of at leaft thirty
different mines t; nor has any per-
:
* Gebri Chem. L. I. C. XIX.
fon
Lifter de Fontibus, Cap. II. S. 9, 10.
(305)
fon fince his time, found lead wholly
free from filver. The Derbyshire lead
has been ſaid to contain two grains
of filver in a pound of lead *.
Every general obfervation of this
kind is liable to much contravention.
from particular facts; becaufe the
quantity of filver contained in lead,
is not only different according as the
lead is fluxed from the ore of differ-
ent mines, but it is very poffible in
an aſſay of the ore of the fame mine,
to meet with one piece of ore which
fhall afford a lead yielding eight or
ten times as much filver as another
piece would do. This diverfity ariſes
from the ore itſelf being variable in
quality in different parts of the fame
mine; and even different lumps of
ore, though contiguous to each other,
Oper. Min. Explicata, p. 263.
U
VOL. II.
will
(306)
will often yield very different quan.
tities of filver, from the fame quan-
tity of lead. This obfervation may
explain the reaſon of the very oppo-
fite teftimonies, which have been
fometimes given in courts of juſtice,
concerning the richness of a mine
from particular affays; the plaintiffs
and defendants, where the iffue to
be tried was the quantity of ſilver,
having been feverally intereſted in
getting the best and the worft pieces
of ore affayed, in order to fupport
their respective claims. There was a
notable inſtance of this with refpect
to the lead mine of Eft kyr-kyr in
Cardiganshire, which was difcovered
in 1690. The law at that time ad-
judged every mine to be a royal mine
the metal of which contained enough
of gold or filver to compenfate the
charges
( 307 )
charges of refining, and the lofs of
the bafer metal in which they were
contained. In confequence of this
law, the patentees of royal mines
laid claim to the mine of Eft-kyr-kyr
which was rich in filver, and they
produced proof in Westminster-ball,
that the lead of that mine contained
to the value of fixty pounds of filver
in every ton; whilft the proprietor
produced proof, that it only contain-
ed to the value of four pounds of
filver in a ton *.
I have been informed by an in-
telligent perfon, that there are fome
lead ores in Great Britain, which,
though very poor in lead, contain
between three and four hundred
ounces of filver in a ton of the lead.
It is not to be expected that the pro-
prietors
→ Some Account of Mines, pa 27 a
U 2
(308
( 308 )
prietors of theſe, or of any other
mines rich in filver, fhould be for-
ward in declaring to the world the
quantity of filver which they con-
tain. The proprietor indeed of a
lead mine containing filver, may
work the fame, without any appre-
henfion of its being taken from him,
under the pretence of its being a
royal mine; yet the crown, and per-
fons claiming under it, have the right
of pre-emption, of all the ore which
may be raiſed. There was an act of
parliament paffed in the fixth year
of William and Mary, intitled,-An
act to prevent difputes and contro-
verfies concerning royal mines. -
This act gave great quiet to the fub-
ject, by declaring, that every propri-
etor of a mine of copper, tin, iron,
or lead, fhould continue in poffeffion
of
( 309 )
of the faid mine, notwithſtanding its
being claimed as a royal mine, from
its containing gold or filver: but it
further enacted, that their majefties,
their heirs and fucceffors, and all
claiming under them, fhould have
the privilege of purchafing all the
ore which ſhould be raiſed out of
fuch a mine, at the following prices;
that is to fay, paying for all ore
waſhed, made clean, and merchant-
able, wherein is copper, after the
rate of fixteen pounds a ton; for tin
ore (except that raiſed in Devonshire
and Cornwall) forty fhillings; for
iron ore forty fhillings; and for lead
ore nine pounds a ton. This ftand-
ard price of nine pounds a ton for
lead ore was, at the time it was fix-
ed, much higher than the ordinary
price of ore, in which there was no
filver
U 3
( 310 )
filver worth extracting; the beſt
kind of Derbyſhire lead ore being,
at prefent, generally worth no more
than ſeven pounds a ton. It may
deſerve, however, the confideration of
the legislature, whether the claufe in
the forementioned act, refpecting the
right of pre-emption, ſhould not be
wholly repealed; as there may be
many lead mines in England very
rich in filver, but which, on account
of the difficulty of working them,
cannot be entered upon with advan-
At
tage, whilft this right fubfifts.
many lead mines, moreover, there
are large quantities of fteel-grained
ore raiſed together with the ordinary
fort, now it generally happens that
the ſteel-grained ore is much richer
in filver than the ordinary diced ore
of Derbyſhire; and it might, if ſepa-
rated
(311)
rated from the reft, be worked for
filver; but whether from an appre-
henfion of the operation of the clauſe
we are fpeaking of, or from mere
ignorance or inattention, all the forts
of ore are mixed and fmelted toge-
ther.
Silver has formerly been extracted
from lead in a great many places in
this ifland. In the reign of Edward I.
near 1600 pounds weight was ob-
tained, in the courſe of three years,
from a mine in Devonshire, which had
been diſcovered towards the begin-
ning of his reign; this mine is called
a filver mine by the old writers, but
it appears to have been a mine of
lead which contained filver *. The
lead
* Hollingfhed's Chron. Vol. II. p. 316.
See alfo, in the fame author, a further account
U 4
of
( 312 )
>
lead mines in Cardiganshire have at
different periods afforded great quan-
tities of filver: Sir Hugh Middle-
ton is faid to have cleared from
them two thouſand pounds a month *
and to have been enabled there-
by to undertake the great work of
bringing the new river from Ware to
London; and in allufion, probably,
to theſe two great circumstances of
his life, there are painted upon fome
of his pictures the two terms-fontes
-fodina. Theſe fame mines yield-
ed, in the time of the great rebellion,
eighty ounces of filver out of every
ton of lead, and part of the king's
army was paid with this filver, which
was
of filver extracted from the lead in Devonshire
and Cornwall in the time of Edward III. p.
413.
* Oper. Min, explic. p. 245.
( 313 )
(313
was minted at Shrewsbury. A mint
for the coinage of Welch filver had
before that time been eſtabliſhed in
1637 at Aberystwith; the indenture
was granted to Thomas Bufhel for the
coining of half- crowns, fhillings,
fix-pences, two-pences, and pennies,
and the monies were to be ftamped
with the oftrich feathers on both
fidest. In the year 1604 near three
thouſand ounces of this Welfh bul-
lion were minted, at one time, at the
Tower. Webster, in his Hiſtory of
Metals, publiſhed in 1671, makes
mention, from his own knowledge,
of two places in Craven, in the weft-
riding of Yorkshire, where formerly
good filver ore (lead ore abounding
* Sir J. Pettus, Effay on Metal. Works.
Rym. Foed. Tom. XX. 164.
Some Account of Mines, p. 6.
in
(314)
in filver) had been gotten. One of
the places was Brunghill moor in the
parish of Slaidburn, the ore of which
held about the value of fixty-feven
pounds of filver in a ton: the other
was Skelkorn field within the townſhip
of Rimmington in the parish of Giſ-
burn; it had formerly belonged to
one Pudfey, who is fuppofed to have
coined the filver he got out of his
mine, there being many fhillings
in that country which the common
people called Pudfey's fhillings *.
There is not at prefent any place
in Derbyshire where filver is extracted
from lead. A work of this kind
was eſtabliſhed a few years ago not
far from Matlock, and the lead yield-
ed fourteen ounces of filver from a
ton; but the mine which afforded
the
Webſter's Metal. p. 21.
( 315 )
the ore was foon exhauſted, or be-
came too difficult to be worked with
profit.
There is a lead mine in
Patterdale near Kefwick, which yields
between fifty and fixty ounces of fil-
ver from a ton of the lead : the ore of
this mine is reckoned to be poor in
lead; and indeed it is very common-
ly obferved, that the pooreft lead
ores yield the moft filver, fo that
much filver is probably thrown away,
for want of having the ores of the
poorest fort properly affayed.
The quantity of lead fielted an-
nually in Derbyshire, may be eſti-
mated at 7,500 tons upon an average;
fifty years ago the average was, pro-
bably, 10,000 tons a year, but we
put it high enough in fuppofing it,
at prefent, to amount to 7,500 tons:
I have never been able to get any
proper
(316)
proper information, concerning the
quantity of lead annually fmelted in
other parts of Great Britain, but for
the illuftration of the fubject we
are upon, let us fuppofe, that in the
whole kingdom 30,000 tons of lead
are annually fmelted, and that at a
medium each ton of lead would
yield 12 ounces of filver; then would
there be, if all the lead was refined,
a faving of three ounces of ſilver
from each ton of lead, or ninety thou-
fand ounces in the whole; our Eng-
liſh workmen reckoning that nine
ounces of filver are full adequate
to the expence of refining a ton of
lead, added to that of the lead
which is loft during the operation.
The general manner of extracting
filver from lead is every where the
fame; it is very fimple, depending
upon
( 317 )
upon the different effential proper-
ties of the two metals. It is an
effential property of lead, when
melted in the open air, to loſe its
metallic appearance, and to burn
away into a kind of earth. It is
an effential property of filver not to
burn away, or to loſe its metallic ap-
pearance when expofed to the action
of the ſtrongeſt fires, in the open air.
Hence, when a maſs of metal, con-
fifting of lead and filver, is melted
in the open air, the lead will be
burned to aſhes, and the filver re-
maining unaltered, it is eaſy to un-
derſtand how the filver may be ex-
tracted from the lead; for being hea-
vier than the ashes of the lead, and
incapable of mixing with them
(fince no metal is mifcible with an
earth), it will fink to the bottom of
the
( 318 )
the veffel in which the mafs is melt-
ed. Iron, tin, and copper, reſem-
ble lead, in being convertible into
a kind of afhes, when expofed to the
action of air and fire, and gold re-
fembles filver in not undergoing any
change from fuch action; hence ei-
ther gold or filver, or a mafs con-
fifting of both, may be purified from
any or all of theſe metals by the
mere operation of fufion; for theſe
metals will rife to the top of the
veffel, in which the fufion is made,
in the form of an earth or droſs, leav-
ing the gold or filver pure at the
bottom.
The ancients certainly knew that
filver could be purified from the
bafe metals by the force of fire.-
The boufe of Ifrael is to me become
drofs: all they are brass (copper), and
2
ting
(319)
tin, and iron, and lead, in the midst of
the furnace, they are even the drofs of
filver. And as we read of filver
being purified ſeven times in a fur-
nace of earth, it may, perhaps be
inferred, that the method of refining
filver, which was then in ufe, con-
fifted in reducing the bafe metals
into earth, by a repetition of the
procefs of fufion.
This inference,
it muſt be owned, is rendered doubt-
ful by a paffage in Jeremiah ;—the
bellows are burned, the lead is confumed
of the fire, the founder melteth in vain ‡.
-This paffage is fomewhat ambi-
guous, and interpreters tranflate the
original Hebrew differently, but
moſt of them collect from it, that the
founder
* Ezek. xxii. 18.
Jerem. vi. 29.
Pf. xii. 6.
(320)
founder added lead to the mixed
mafs which he wanted to refine.
Lead, when reduced to an earth
by being burned in the open air,
may, in a ſtronger degree of heat,
be converted into a yellowish glaſs *,
which
* Other metallic fubftances yield coloured
glaffes, either when vitrified alone, or in
conjunction with pure glaſs. In enamel and
china painting, they prepare rofe red and
purple colours from gold; fcarlet reds from
iron, or vitriols that partake of it greens
;
from copper; blues from cobalt blacks
from magnefía, zaffer, and ſcales of iron; yel.
lows from filver antimony, Naples yellow,
and crocus martis; white from tin. The
ſame ſubſtance yields different colours, ac-
cording to the degree of heat to which it is
expoſed; thus, the green colour of common
glafs bottles, which proceeds from the iron
contained in the fand and vegetable aſhes from
which the glafs is made, is changed into a blue.
by a ſtronger degree of heat.
(321)
which has the property of greatly
contributing to the eafy vitrification
of all earthy fubftances; hence, when
gold or filver are mixed with iron,
copper, or tin, it is ufual to add to
the mixed maſs a quantity of lead,
in order to accelerate the purification;
for the lead will be converted into
glafs, and this glafs will vitrify all
the extraneous fubftances with which
the gold or filver are polluted, with-
out exerting the leaft action upon
the precious metals themfelves.
I do not know upon what grounds
one of the most diftinguished che-
mifts of the age has afferted, "that
the refining of gold and filver mere-
ly by the action of the fire was the
only method anciently known;" f
and
Chem. Dist. by M. Macquer, artic.
Refining.
VOL. III.
X
(322)
and that the doing it by the addition
of lead, is a difcovery with which
the ancients were unacquainted.
Not to infift upon what has been
quoted from Jeremiah; in Diodorus
Siculus there is a very minute de-
fcription of the manner of working
fome gold mines in the confines of
Egypt and Arabia; this defcription
was probably written on the ſpot
when he visited that country, but
the mode of operation feems to have
been derived from a more early pe-
riod; as the diſcovery of the mines is
attributed by him to fome of the moſt
ancient Egyptian kings; amongſt
other particularities, he takes notice
of their melting the mineral in con-
junction with a little tin, fome fmall
portion of falt, and a lump of lead.*
Sirabo
*Diod. Sic. Lib. III. p. 183-189.
(323)
Strabo quotes Polybius as fpeaking of
a filver ore, which, after being five
times washed, was melted with lead,
and became pure filver. Unfortu-
nately this part of the works of Po-
lybius is loft, or we might have had
a more circumftantial knowledge of
the proceffes by which the ancients
extracted filver from its ores, as
Strabo fays, that he omitted Poly-
bius's account of this matter, becaufe
of its prolixity. Pliny probably
has an allufion to the ufe of lead in
refining filver, when he fays, that a
filver ore in the form of an earth
could not be melted except in con-
junction with lead or the ore of lead.†
A more diligent fearch into the writ-
ings of the ancients would, doubt-
*
*Strab. Geo. Lib. II. p. 221.
Plin. Hift. Nat. Lib. XXXIII. C. 6.
lefs,
X 2
(324)
lefs, furniſh more authorities upon
the point, but theſe may be ſuffi-
cient to induce us to believe, that
they were not unacquainted with the
uſe of lead in refining gold and fil-
ver. But to return to the manner
of extracting filver from lead.
The veffel in which the workmen
melt the maſs of filver and lead, is
of a ſhallow form, that a large fur-
face of the melted mafs may be ex-
pofed to the air; it is made ufually of
four meaſures of the afhes of calcined
bones, and of one meaſure of un-
waſhed fern afhes, and is called a
teft:* This veffel is very porous,
but
* Teſts are ſometimes made of clay and
other materials, and metallurgic writers of
ten order the wood afhes to be waſhed, leſt
the alkaline falts which they contain fhould
tend to vitrify the teft; but a very good re-
finer
(325)
but not fo much as to imbibe the
metal, whilst it continues in the form
of a metal; but as the earth, into
which the lead is foon reduced by
the action of the fire, becomes melt-
ed, the teſt imbibes a portion of it
in that liquid ftate, the other por-
tion is driven off (as cream is blown
off from milk) from the furface of
the melted mafs, by the blaft of a
bellows. The liquid, half vitrified,
earth of lead, which is thus driven
off, concretes into hard maffes of a
fcaly texture, and is called in that
ftate litharge, or filver ftone, from
the manner of its being produced,
or from an idle notion of its con-
taining
finer at Holywell informed me, that he always
uſed the aſhes without waſhing them, as the
veffel became thereby lefs apt to crumble into
pieces.
x 3
(326)
taining much filver. The litharge
which is firft formed is whitiſh, that
which experiences a greater degree
of heat is red; the colour of the
litharge is alfo influenced by that of
the other metals, which may chance
to be mixed with the mafs of lead
and filver. When the furface of the
melted maſs becomes white, and
throws up no more litharge, the ope-
ration is finiſhed; but as the re-
maining filver is not quite pure,
fince it contains a fmall portion of
lead, from which the degree of heat
requifite for melting the mixed maſs
cannot readily free it, it is taken to a
refining furnace, and rendered quite
pure, at leaſt from lead, by cupella-
tion. This procefs confifts in melt-
ing the filver obtained from the firſt
operation, in a veffel made of the
fame
2
( 327 )
fame materials as the teft, and which,
from its refemblance to a wide-
mouthed cup, has been called a
supel. The cupel being expofed to
a ftronger heat than the teft, the lead
which had eſcaped the action of the
fire on the teft, is now driven out
from the filver, and being converted
into litharge, is abforbed by the cu-
pel, and by this means the filver is
purified from every metal except
gold; for it is not neceffary, on this
occafion, to remark, that a minute
portion of copper, when there hap-
pens to be any in a maſs of filver and
lead, probably eſcapes the action of
the fire in cupelling gold or filver.
There are ſeveral fmelting houfes
at Holywell in Flintshire, where filver
is extracted from lead; Mr. Pennant *
× 4
* Tour through Wales.
has
(328)
has given the following account of
the quantity of filver extracted at
one of the largest of thefe houfes in
the courſe of fix
-
years.
ounces.
ounces.
Year 1754 12160 Year 1774 - 5693
1755 - 1276
*
1775 6704
1756- 7341
1776 - 4347
The filver obtained from lead at
Holywell, is chiefly fold to the manu-
facturers at Birmingham and Sheffield.
Much filver is alfo extracted from
lead in Northumberland.
At Holywell they ufually work off
three tons of lead at one operation,
the quantity of filver which they
procure, is variable according to the
richneſs of the lead; a few years.
ago they were refining lead from an
ore found in the Iſle of Man, and it
gave them about 60 ounces at every
ope-
!
(329)
་
operation, or 20 ounces in a ton of
the lead. The litharge ordinarily
obtained from three tons of lead
amounts to 58 hundred weight; this
litharge may either be changed into
red lead by calcination, or it may be
reduced into lead again by being
Aluxed with charcoal, or any other
matter containing the inflammable
principle, but when it is reduced
they feldom obtain more than 52
hundred weight of lead, fo that by
ex-
* Lead from litharge is, generally ſpeak-
ing, worth five fhillings a ton more than ore
lead, as the plumbers eſteem it ſofter and fitter
for making fheet lead; yet the litharge lead
from the ore of the Ifle of Man here mention-
ed, was found quite unfit for making fheet
lead, on account, probably, of the ore having
held other metals befide filver and lead.
In the foreign works they eftimate the
lofs of weight, which the litharge fuftains in
being
(330)
extracting the filver, there is a lofs
of eight hundred weight in three
tons of lead. It has been faid that
the Dutch can extract the filver from
three tons of lead, and not loſe above
fix hundred weight upon convert-
ing the litharge into lead, and that
this fuperior ſkill, aided, probably,
by their fuperior induftry, enabled
them to purchaſe our lead, and to
extract the filver from fuch as could
not be refined here with advantage:
I have been informed, however, by
an experienced refiner in Derbyshire,
that he could extract the filver with-
out lofing quite fo much as fix bun-
dred
being reduced into lead, at a fixth part of the
weight of the litharge, or 93 hundred weight
from 58 hundred weight of litharge. Effais
des Mines, Tom. II. p. 401.
* Webſter's Metal. p. 233.
( 331 )
dred weight in three tons of lead; I
make no queſtion that the lofs de-
pends, in fome meaſure, on the qua-
lity of the lead. It has been re-
marked before, that lead, which does
not contain nine ounces of filver in
a ton, is not thought worth the re-
fining; the fmalleft quantity which
can be extracted with profit, muft
depend much upon the price of lead,
all expences attending the feveral
proceſſes being the fame. For eight
hundred weight of lead, which may
be affumed at a medium as the lofs
fuftained during the operations of
refining and reducing, is worth 61.
when lead is at 151. a ton, and it is
worth only 41. 16s. when it is at
121. a ton. The value of 27 ounces
of filver, which we ſuppoſe to be the
quantity feparable from three tons
of
( 332 )
1
of lead, is 71. 1os. 9d. at 5s. 7d, an
ounce; hence, the difference be-
tween the value of the filver obtain-
ed, and that of the lead loft, would,
when lead is at 151. a ton, be
>
Il. 10s 9d. and when lead is as low
as 121. a ton, it would amount to
21. 145. gd. In the times of Sir
John Pettus, the ufual allowance for
waſte in refining and reducing of
lead, was three hundred weight in a
ton, or nine hundred weight in three
tons, and the lead was valued at
12l. a ton, * fo that lead has altered
very little in its price in the courſe
of above one hundred years.
Silver is here valued at 5s. 7d.
an ounce; this requires fome ex-
planation. A pound of standard
filver in England, confifts of 11
Fodina Reg. p. 10.)
ounces
( 333 )
ounces and 2 pennyweights of fine
filver, and of 18 pennyweights of
copper; in other words, every mafs
of Standard -filver confifting of 40
parts by weight, is compofed of
37
parts of fine filver, and of 3 parts of
copper; the copper is called the al-
oy. All nations ufe fome alloy both
in their gold and filver; partly with
a view of rendering thefe metals
harder, and partly becauſe it would
require much labour and expence to
free them wholly from that fmall
portion of copper, which, in their
ordinary ſtate, as fluxed from their
ores, they are generally found to
contain. A pound of ſtandard ſilver
is coined into 62 fhillings, hence the
Mint price of an ounce of ſtandard
filver would be a twelfth part of 62
Thillings, or 5s. 2d.
From hence
it
( 334 )
it might be fhewn, by the rule of
proportion, that the market price of
an ounce of fine filver, which con-
tains no copper, will be 5s. 7d. at
the leaft. The market price of fil-
ver bullion does not wholly depend
on the mint price, it can never be
lower than that, but, from the ope-
ration of various caufes, it may ex-
cced it. Standard gold with us
confifts of 11 parts of fine gold, and
of part of copper, or of a mixture
of filver and copper; and a pound
or 12 ounces of ftandard gold, is
coined into 44 guineas; hence the
price of an ounce of ftandard gold is
31. 17s. 10 d. and the price of an
ounce of fine gold is 41. 4s. 114d.
Foreign gold trinkets ftain the
hands more, and have a more cop-
I
2
pery
Effay on Money and Coins, p. 2. and 55.
(335)
pery look than English ones; and
in fact they are made of gold which
is alloyed with a much greater pro-
portion of copper, than the ftand-
ard gold of England; yet, when an
enamel is to be fixed on gold, one
of the most experienced of the fo-
reign enamellers recommends the
ufe of gold, which has the fame al-
loy as the English ftandard gold, or
two parts alloy, and twenty two
parts of fine gold.
Copper communicates a fmell
both to gold and filver. The Ro-
man ſpecula, which they uſed as look-
ing glaffes, in Pliny's time were
commonly made of filver, but the
filver was alloyed with much cop-
per; for we find a cunning waiting
maid in Plautus advifing her mif-
trefs
† M. de Montamy, Traite des Coleurs.
(336)
treſs to wipe her fingers after hav-
ing handled a fpeculum, left her
paramour, from the finell of her
fingers, ſhould fufpect her of having
received filver from fome other.
lover.
Ut fpeculum tenuifti, metuo ne oleant argen-
tum manus,
Ne ufque argentum te accepiffe fufpicetur
Philolacles.
Plaut. Moît. Act. I.
ESSAY
ESSAY X.
OF RED AND WHITE LEAD.
F the reader does not know what
IF
minium or red lead is, I would
with him to fend for a few ounces
of it to his painter or apothecary.-
Suppofing him to have a parcel of
red lead before his eyes, the firſt
thing which will ftrike him is its vi-
vid colour verging a little towards
orange; if he crumbles it between
VOL. III.
Y
his
( 338 )
-
his fingers, he will find it to be an
almoſt impalpable powder; if he
poizes it in his hand, he will per-
ceive it to be much heavier than
either brick duft or red ochre,
with which fubftances it is fome-
times adulterated; if he compares
it with a piece of lead, he will be
aftoniſhed how it can be either pro-
duced from lead, or be capable of
being, by a very flight operation,
reduced into lead again.
It has been mentioned in the pre-
ceding Effay, that red lead is made
from litharge at Holywell: this red
lead, which is made from litharge, is
not perhaps, in all its properties, of
quite the fame kind with that which
is made directly from lead; at leaſt
I have been informed, that the mak-
ers of Alint glafs, who uſe much red
lead
( 339 )
lead in the compofition of that glaſs,
are of opinion, that the litharge red
lead does not flux fo well as that
which is made from the direct cal-
cination of lead, as is practifed in
Derbyshire. There are in that county
nine red-lead mills or furnaces, all of
which are much upon the fame con-
ftruction.
The furnace is very like a baker's
oven, its vaulted roof is not at a great
diſtance from the bottom or floor, on
each fide of the furnace there are
two party walls, rifing from the
floor of the furnace, but not reach-
ing to the roof, into the intervals,
between thefe walls and the fides of
the furnace, the pit-coal is put, the
flame of which being drawn over
the party walls, and ſtriking upon
the roof, is from thence reflected
down
Y 2
(340)
down upon the lead, which is placed
in a cavity at the bottom, by which
means the lead is foon melted. The
furface of melted lead, when expofed
to the open air, inftantly becomes
covered with a dufky pellicle; and
this pellicle being removed another
is formed, and thus by removing the
pellicle, as faſt as it forms, the great-
eft part of the lead is changed into
a yellowish green powder. This
yellowish powder is then ground
very fine in a mill, and being waſhed,
in order to ſeparate it from ſuch parts
of the lead as are ftill in their me-
tallic ftate, it becomes of an uni-
form yellow colour, and, when it is
dried to a proper confiftency, it is
thrown back again into the furnace,
and being conſtantly ſtirred, fo that
all its parts may be expofed to the
action
( 341 )
action of the flame of the pit coal,
in about 48 hours it becomes red
lead, and is taken out for uſe.
The colour of the red lead admits
fome variety, which is occafioned by
the different degrees of heat. If
the heat is too fmall, inftead of red
it is yellow or orange coloured; if it
is too great, the red colour is chang-
ed into a dirty white, between theſe
two extremes it is fubject to fome di-
verfity of ſhades of red, which cannot
well be noticed or deſcribed, except
by thoſe who are engaged in the
making of it.
It has been afferted, that the re-
verberation of the flame and ſmoke
upon the furface of the lead, is not
a neceffary circumftance in giving it
a red colour, but that it will ac-
quire
*Inftit. de Chym. par M. Demachy, p. 522.
Y 3
(342)
quire this colour by a long calci-
nation without coming into contact
with the flame. The truth of this
affertion I think may be doubted. I
have more than once calcined lead
for above 60 hours, without fuffer-,
ing the flame of the fire to touch it
during any part of the proceſs, but
by this method I could never obtain
any thing better than a dirty red,
reſembling the red of brickduft,
which is very different from the
colour of red lead; and even this
dirty red was changed into a yellow
colour, by augmenting the degree of
heat with which the lead had been
calcined. The method of making
red lead is very well underſtood in
England and Holland, but not in
France; and the French workmen are
of
(343)
of opinion that it cannot be made
by the flame of wood fires*.
During the making of red lead,
part of it is volatilized, there rifes
up from it a vapour, which attaches
itſelf to the roof of the furnace, and
forms folid lumps. Thefe lumps
are of a yellowish white colour mix-
ed with pale green and ſome reddiſh
ſtreaks, wherein are frequently finall
red cryſtals, reſembling ſuch as may
be artificially formed by fubliming
fulphur and arfenic together. The
workmen call the whole of what is
ſeparated from the lead in the form
of fmoke, fulphur: when this fub-
limed matter is detached from the
roof of the furnace, the red parts
* Mem. de l'Acad. des Scien. 1770.
Elemens de Mineral, par M. Sage. Vol. II.
P. 248.
Y 4
are
( 344 )
are converted by a fubfequent pro-
cefs, into red lead; and the yellow
ones are fent to the fmelting fur-
naces, to be run down again into
lead. The quantity of this fubli-
mate amounts to about five hundred
weight in making one hundred tons
of red lead. The proportion here
affigned is not wholly to be relied
on, fince the fmoke arifing from the
lead forms itſelf into larger maffes,
and in lefs time, when it is not con-
ſtantly ſwept from the roof of the
furnace than when it is; and the
workmen endeavour to keep the
roof as free from it as they can, be-
cauſe a ſmall portion of it injures
the colour of a large quantity of the
red lead with which it happens to
be mixed.
A ton or twenty hundred weight
of
(345)
of lead generally gives twenty-two
hundred weight of red lead, notwith-
ſtanding the lofs of fubftance which
the lead evidently fuftains from the
copious ſmoke which arifes from it
during the operation. Some authors
tell us, that the increaſe in the weight
of the red lead is double what I have
here mentioned: thus, Orfchall fpeak-
ing of the red lead made at Nurem-
berg, affures us, that 100 pounds of
lead yield 120 pounds, and fome-
times even more, of red lead. It
is not impoffible that, according to
the different manners of conducting
the procefs, there may be a differ-
ence in the quantity of weight which
the red lead acquires: I had my in-
formation from fome of the moſt
1
expe-
* Orfch. Metal. French Tranſ. p. 100.
M. Sage's Miner. Vol. II. p. 384.
( 346 )
experienced makers of red lead in
Derbyshire. There have been great
difputes amongſt philofophers, to
what principle this increaſe of weight
fhould be afcribed; fome have attri-
buted it to what they call the matter
of fire; others are upon good grounds
convinced, that it is owing to the
abſorption of the air itſelf, or of
fome of the principles of which the
air confifts. This hypothefis con-
cerning the fixation of air during the
calcination of metals, is faid to have
been firſt advanced by John Rey, a
French phyſician, in 1630; Dr. Hales
was partly of the fame opinion *;
and Dr. Pemberton very exprefsly af-
firms, that calcined metals receive
their increaſe of weight from the air,
which," by acting on the inflamma-
ble
*Veget. Stat.
( 347 )
ble fubftance, either in metals or
other bodies, expels it from them,
and unites itſelf (in part at leaſt) to
the remains of the body." The
ingenious labours of Dr. Priestley and
of M. Lavoisier have confirmed the
conjectures and experiments of for-
mer philofophers, for they have
clearly proved two points-firſt,
that a large portion of air may be
Separated from red lead, by reducing
it to the ftate of a metal;—and
fecondly, that a large portion of air
is abforbed by lead during the calci-
nation, by which it is reduced to
the ſtate of red lead †.
During the calcination of lead, it
is certain, from what has been faid,
that
Pember. Chem. p. 245.
+ Priestley's Exper. and Lavoifier's Effays,
tranflated by Henry.
( 348 )
that much of its fubftance is difperf-
ed into the air; this fubftance may
indeed be ſeen aſcending as a ſmoke
from the ſurface of the lead, if the
heat be fo great as to make it boil;
and in a lefs degree of heat, the va-
pour which afcends from it, may be
rendered viſible, by holding over it
a wet iron ladle to condenſe it. But
at the fame time that the lead lofes
confiderably of its weight by the
volatilization of part of its fubftance,
it receives fuch an acceffion of new
matter from the air, as renders the
weight of the part which remains
much greater than that of the whole
lead which was expofed to calcina-
tion. This acceffion of aërial matter
may be driven off from red lead, by
reſtoring to it the inflammable prin-
ciple which was confumed during
the
349)
the calcination; but after this extra-
neous matter is driven off by re-
ducing the lead, we ought not to
expect that the lead, which is thus
brought back to its former ftate,
fhould weigh as much as it did be-
fore it was calcined; becauſe that
part of it which was volatilized and
diſperſed into the air cannot be re-
covered. And in fact, it was obſerved
in the laſt Effay, that three tons of
lead, when converted by calcination
into litharge, had loft two hundred
weight; this quantity, and, probably,
much more than this, had been vo-
latilized and loft, for the remaining
fifty-eight hundred weight conſiſted
partly of the earth of lead, and partly
of the air which had been fixed in it
during the calcination; and hence,
when it was reduced, it did not give
above
(350)
above fifty-two hundred weight. In
calcining then, and reducing fixty
hundred weight of lead, there is a
lofs of eight hundred weight: a great
part of this lofs is rightly referred to
the volatilization of the lead, but a
part alſo may juftly enough be re-
ferred to the fcoria which remains
after the reduction of the litharge
into lead, that operation being fel-
dom performed fo accurately as not
to leave fome part of the litharge
unreduced. I have here fpoken of
the lofs of weight ſuſtained during
the reduction of litharge, as if it
was the fame as that which red lead
fuftains; there probably may be
fome difference between them, but
the general inference is the fame;
and I have been informed moreover,
that there is neither increaſe nor de-
creaſe
( 35 )
creaſe in weight in converting li
tharge into red lead*.
In making red lead in Derbyshire,
the workmen mix one hundred
weight of flag lead with about eigh-
teen hundred weight of ore lead;
and they are perfuaded that this flag
lead has a great effect, in accelerating
the converſion of the other lead into
an earth. Tin, when mixed with
lead, very much promotes its calci-
nation; and the flag lead has this
..
pro-
* This obfervation does not accord with
that of the author of the Familiar Difcourfe
concerning Mines, p. 34. 20 hundred
weight of this litharge will produce 22 hun-
dred weight of red lead." Another author
informs us that 20 pounds of lead will, by a
long calcination, give 25 pounds of aſhes, and
that theſe 25 pounds of afhes will, when re-
duced, give 19 pounds of lead. Lemery Cours
de Chym. p. 145.
2
J
(352)
property in common with a mixture
of tin and lead, that it does not,
when melted, exhibit any colours on
its furface: may not its properties,
'by which it is diſtinguiſhable from
ore lead, arife from its containing
zinc or tin? We are too apt, I think,
to look upon the ores of lead as con-
taining only one metal; fince we are
certain that they all contain two,
namely, lead and filver; and it may
be, that they contain other metallic
fubftances, particularly zinc and tin.
In converting a ton of lead into
red lead, the workmen obferve, that
towards the end of the operation,
a few pounds of lead are always
found to remain, which cannot be
changed into red lead, with the fame
facility with which ordinary lead is
changed. When I was firft informed,
of
( 353 )
-
df this circumftance, I confidered
it in the following manner. Der-
byshire lead, though it does not con-
tein filver enough to render the ex-
traction of it profitable, yet it gene-
rally contains five or fix ounces in a
ton: filver is not capable of being
converted into an earth by the ac-
tion of air and fire, when therefore
a ton of lead is converted, as to its
greateft part, into red lead, why may
not the fix ounces of filver contained
in that lead be left unaltered? and
may not the fuperior difficulty of
reducing the laſt portion of the lead
into red lead, proceed from hence,
that it is much more impregnated
with filver, than ordinary lead is?
Under the influence of this conjec-
ture, I procured from Derbyſhire,
fome of the lead which remained:
VOL. III.
Z
un-
()
( 354 354
uncalcined in the making of red
lead, and I affayed it for filver,
but it did not contain more filver
than many ſpecimens of ore lead
contained.
It has been remarked, more than
once, that red lead may be reduced
into lead, by being melted with rofin,
tallow, charcoal, or any fubftance
containing the inflammable princi-
ple. The proof of this is very eafy;
a few grains of red lead being fcat-
tered on a piece of red-hot charcoal,
will be changed into globules of
lead; or if the reader burns a com-
mon red wafer in the flame of a
candle, holding a piece of white
paper under it, he will fee many
red-hot globules falling upon the
paper, and theſe globules he will find
to be lead this lead proceeds from
I
the
( 355 )
the red lead with which ordinary
wafers are coloured, being reduced
into the ſtate of a metal, by uniting
itſelf with the inflammable principle.
The best wafers are coloured with
vermilion-powdered cinnabar *.
Having been difappointed in the
expectation of finding a large pro-
portion of filver, in the fall refidue
of lead remaining after the conver-
fion of ordinary lead into red lead;
and being unwilling to give up the
notion, I was defirous of convincing
myſelf that I had not been guilty of
any mistake in the affay that I had
made, by trying whether red lead it-
felf did not contain filver; for if red
lead contained filver, I faw no reaſon
to
* Cinnabar is an ore of quickfilver; it is
compofed of quickfilver and fulphur; gene-
rally of 7 parts of quickfilver to 1 of fulphur.
Z 2
( 356 )
356)
to be ſurpriſed at the refidue,, before
mentioned, not containing more than
I found it to do. I therefore re-
duced a quantity of red lead into
the ſtate of a metal, by melting it
with rofin; this reduced lead was
carefully affayed more than once,
and it always afforded a portion of
filver. Hence we may conclude,
that the filver contained in lead,
though it be not fubject to calcina-
tion during the process of making
red lead, is nevertheleſs mixed with
the calcined lead in fuch, a commi-
nuted ſtate, as to escape our ſenſes;
the filver, probably, is ftill in the
form of filver, but its particles are
fo indefinitely fine, that they can-
not be diftinguished in the mafs of
red lead, which contains them.
The method of making flag lead
has
ས
( 357 )
has been defcribed before; I affayed'
this kind of lead feveral times, and
I fometimes obtained from it a glo-
bule of filver, at other times there
was no appearance of filver. This
difference in the refult of the affays,
is not to be attributed to any differ-
ence in the quality of the flag lead
which was affayed, for all the pieces
which I tried were cut from the
fame lump, but to the different de-
grees of heat ufed in the operation;
when the fire was too ftrong, the
filver, I conceive, was volatilized.
Silver, I know, is looked upon as a
fixed metal, and not capable of being
volatilized; and the lofs of filver,
when the fire is too ftrong, has been
attributed to its not being volatiliz-
ed, but abforbed by the cupel: I
have no objection to this account;
Z 3.
but
(358)
but that the volatilization of filver
on the cupel is no unwarranted con-
jecture, appears from hence, that in
the laft procefs of refining lead for
filver at Holywell, fo much of the
filver is carried into the chimney of
the furnace, that they have pro-
cured a filver cup from melting the
fweepings.
A great quantity of lead is annu-
ally imported in the tea boxes from
China; a Congo box contains about
10 pounds, and an Hyfon box about
4 pounds of lead; I have frequently
affayed this lead, and always found
that it contained filver, but not in
quantity fufficient to quit the ex-
pence of extracting it.
Pure lead is heavier than pure fil-
ver, and the purer the lead the great-
er is its weight; I calculated the
weigh
(359)
weight of a cubic foot of five differ-
ent ſorts of lead :
Weight of a cubic foot of
Lead from the reduction of red lead
Lead uncalcined in making red lead
Lead fmelted from an ore
Lead from the flag of a cupola furn.
Lead from a tea box
Avoir.oz.
11460
-
11331
11262
II 212
11176
The experiments from which I form-
ed this table, were repeated at dif-
ferent times, and the mean of feve-
ral trials in the refpective forts is
expreffed.
A cubic foot of fine
filver weighs 11091 ounces *.
The following affays of the feveral
leads here mentioned, were made by
an experienced affayer in London;
they are very little different from
* Cotes.
Z 4
thofe
2
(360)
thoſe which I myſelf had made, but
I was defirous that the reader might
rely upon the authority of a perſon-
verfed in the particular bufinefs of
affaying, rather than upon mine.
Fine filver in a pound of
Grains.
Lead from the reduction of red lead
1 //
Lead uncalcined in making red lead
11
Lead ſmelted from an ore
Lead from the flag of a cupola furn.
Lead from a tea box
13
I
13
Hla mica molt mit mo't
From comparing the two tables.
together, we fee that the heaviest
lead contains the leaft filver. I do
not think, that perfons intereſted in
knowing the quantity of filver con-
tained in any particular fpecimen of
lead, fhould reſt fatisfied with aſſay-
ing fo fmall a portion as a pound,
efpecially if no notice is taken of
any
(361)
!
any weight less than one fourth of
a grain.
White lead or cerufe, is lead cor-
roded by vinegar. Thin plates of
lead are rolled up in a fpiral form,
and placed in earthen pots contain-
ing vinegar; thefe pots being ranged
on proper ftages, and their mouths
being covered in fuch a manner, as
to permit the vapour of the vinegar
to eſcape, and at the fame time to
prevent any impurity from falling
into them, a quantity of horſe-dung
is thrown in amongst them; by the
heat of which, as it grows putrid,
the vinegar is raiſed in vapour, and
this vapour attaching itfelf to both
fides of every fpiral of the lead,
which is fo placed as not to touch
the vinegar, it corrodes the lead into
white fcales, which being beat off
from
(362)
from the plates, washed and ground
in a mill, conftitute the white lead
of the fhops, excepting that this is
generally, even before it gets into
the hands of the painters, adulterat-
ed with chalk. Cerufe was for-
merly made by the vapour of putrid
urine inftead of vinegar. The time
when this preparation of lead was
firſt diſcovered, is wholly uncertain;
Diofcorides fpeaks of its being made
in great perfection at Rhodes, Corinth,
and Lacedemon, and of an inferior fort
of it at Puteoli*; and Pliny defcribes
two ways of conducting the opera-
tion, both of which are now in uſe †.
The Roman ladies were well ac-
quainted with the ufe of cerufe as a
cofmetic: Plautus introduces a wait-
* Diof. Lib. V. C. 103.
Lib. XXXIV. S. 54.
ing
(363)
ing woman refufing to give her mif-
ftreſs either ceruse or rouge, becauſe,
forfooth, in the true fpirit of a flat-
tering Abigail, fhe thought her quite
handſome enough without them *.
I fuppofe the Chriftian ladies in the
days of St. Jerome, were given to this-
pagan custom, for the venerable fa-
ther inveighs very forcibly againſt
-X
the
non do,. fcita es tu quidem,
Nova pictura interpolare vis opus lepidiffi-
mum,
Non iftanc ætatem oportet pigmentum ullum
attingere,
Neque cerufam, neque melinum, neque aliam
ullam offuciam.
Plaut. Moft. A&t. I.
Quid faciat in facie Chriftianæ purpuriffus
et cerufa, quorum alterum ruborem genarum,
labiorumque mentitur, alterum candorem:
oris et colli, ignis juvenum, fomenta libidi-
num, impudicæ mentis indicia, Hieron. ad.
Fufcum.
!
(364)
the ufe of rouge for the lips and
cheeks, and of ceruſe for the face and
neck, as incentives to luft, and indi-
cations of unchafte defires. With-
out prefuming to explore the arcana
of a lady's toilet, or to reveal the
arts by which my fair countrywo-
men endeavour to improve charms
naturally irrefiftible, I would add
to the admonition of St. Jerome, a
caution more likely, in thefe dege-
nerate times, to be attended to-
the certain ruin of the complexion,
to fay nothing of more ferious mala-
dies, which must ever attend the
conftant application of this drug.
Nor is the magiftery of bifmuth or
Spanish white, as it is called, much
lefs pernicious than cerufe, notwith-
ftanding its being in fuch repute in
London, that the chemifts can hardly
pre-
( 36.5.)
pare it faft enough to fupply the
demand for it *. But if, as is moſt
probable, they will neglect this cau-
tion, I warn them, however, to for-
bear the uſe of ſuch waſhes at Har-
rowgate, Moffat, and other places of
the fame kind, left they fhould be in
the ſtate of the unlucky fair one,
whofe face, neck, and arms were
fuddenly defpoiled of all their beau-
ties, and changed quite black by a
fulphureous water. Indeed, all phlo-
giftic vapours, and even the fun it-
felf, tends to give both the magiftery
of bifmuth, and cerufe, a yellow co-
lour: this obfervation may explain
a line
The magiftery of bifmuth is made by
diffolving that femimetal in aqua fortis, and
precipitating the diffolved biſmuth from the
acid, by water.
( 365 )
a line in Martial, where a cerused
lady is faid to fear the fun *.
Other fluids, befides the vapour
of vinegar, corrode lead into a kind
of cerufe. When plumbers ftrip
the roofs of churches, or other build-
ings covered with lead, which has
lain undisturbed for many years,
they ufually find that fide of the lead
which is contiguous to the boards,
covered with a white pellicle, as
thick fometimes as an half crown;
this pellicle is corroded lead, and is
as ufeful for painting, and other
purpoſes, as the beſt white lead. The
lead on the fouth ſide of any build-
ing is found to abound moft with
cretata timet Fabulla nimbum,
Cerufata timet Sabella folem.
this
Mar. Ep. Lib. II. E. XLI.
(367)
this white cruft; that on the north
fide having very little, or none at all
of it. It is believed alſo, that lead
which lies on deal boards, is not fo
apt to be covered with this white in-
cruftation, as that which lies upon
oak if there be any truth in this
obfervation, it may, perhaps, be ex-
plained from hence, that oak con-
tains a much ftronger acid than deal,
and this ftrong acid being diftilled,
as it were, by the heat of the fun in
fummer, attaches itſelf to the lead,
and corrodes it or this corrofion
may be the effect of the fun and air,
which, by their conftant action, cal-
cine or corrode the lead; and this
calcined lead not being washed off
by the rain, may, in the courſe of a
great many years, form the cruft
here fpoken of. It might be worth
:
while,
(368)
while, in a philofophical view, to
examine more minutely than has
been done, the difference between
old lead which has loft fome of its
parts by long expoſure to the air,
and new lead. The plumbers have
affured me, that if a pig of old lead,
and an equal pig of new lead, be
put together into the fame iron pot,
and expofed to the fame degree of
heat, the new lead will be melted
much fooner than the old lead, An-
other difference betwixt them, re-
fpects the quicknefs with which they
may be reduced to a calx, the new
lead being obferved to calcine much
fafter than the old.
Neither cerufe, nor litharge, nor
minium, have any tafte; but any of
theſe ſubſtances being boiled in di-
filled vinegar, which has an acid
taſte,
( 369 )
tafte, will be diffolved in it; and the
folution being cryftallized will give
one of the fweeteft fubftances in na-
ture, called Saccharum Saturni, or
fugar of lead. It is this property
which lead has of acquiring a fweet
tafte by folution in an acid, that has
rendered it fo ferviceable to thofe
wine merchants who, refpecting their
own profit more than the lives of
their cuſtomers, have not fcrupled
to attempt recovering wines, which
had turned four, by putting into
them large quantities of cerufe or li-
tharge. I believe this adulteration
is puniſhed with death in fome parts
of Germany; and it is to be wifhed
that it met with that punishment
every where. In 1750, the farmers
general in France being aftonished at
the great quantities de vin gaté which
A a
VOL. III.
were
( 370 )
1
were brought into Paris, in order to
be made into vinegar, redoubled
their reſearches to find out the cauſe
of the great increaſe in that article;
for near thirty thouſand hogfheads
had been annually brought in for a
few years preceding the year 1750,
whereas the quantity annually brought
in forty years before, did not exceed
1200 hogsheads. They difcovered,
that feveral wine merchants, aſſum-
ing the name of vinegar merchants,
bought theſe four wines (which were
ftill rendered more four by the cuf
tom of pouring into each hogfhead
fix pints of vinegar before it was
fold), and afterwards, by means of
litharge, rendered them potable, and
fold them as genuine wines *.
Our
*Exam. Chy. de Differ. Subf. par. M.
Sage, p. 157.
( 371 )
Our English vintners, there is rea-
fon to fear, are not lefs fcrupulous
in the uſe of this poifon than the
French wine-merchants; for it not
only corrects the acidity of four
wines, but it gives a richneſs to
meagre ones, and by this property
the temptation to uſe it is much. in-
creaſed.
The reader may foon furnish him-
felf with the means of detecting lead
when diffolved in wine. Let him
boil together in a pint of water, an
ounce of quicklime, and half an
ounce of flour of brimstone, and
when the liquor, which will be of a
yellow colour, is cold, let him pour
it into a bottle, and corking it up,
referve it for ufe. A few drops of
this liquor being let fall into a glafs
of wine or cider containing lead,
Аа 2
will
( 372 )
will change the whole into a colour
more or leſs brown, according to the
quantity of lead which it contains ;-
if the wine be wholly free from lead,
it will be rendered turbid by the li-
quor, but the colour will be rather
a dirty white than a blackiſh brown.
Van Helmont was of opinion, that
Paracelfus made no vain boaft, in
faying that he could cure two hun-
dred diſeaſes by preparations of lead;
but he does not tell us of the many
hundred perfons he, probably, fent
to their graves by his attempt. But
it is beyond my ability, and falls
not within my deſign, to diſcuſs ei-
ther the falubrious or poiſonous
qualities of lead; efpecially as the
labours
* Adeo ut non fruftra Paracelfus glorietur
folo plumbo forte ducentas morborum claffes
fuperare poffe. Helm. Op. p. 563.
(373)
labours of Sir G. Baker and Dr.
Percivalt have fo fully illuftrated
that ſubject.
Having accidentally heard, during
the printing of this volume, that
Dr. Priestley had diſcovered a method
of reducing red lead to its metallic
form, by melting it, in contact with
inflammable air, by means of a
burning glafs, I was very defirous of
having fo remarkable a fact confirm-
ed by other experiments. But being
prevented by a bad ſtate of health
from venturing into an elaboratory
myfelf, I communicated my wishes
and ideas to an ingenious gentleman
of this univerfity, who has for fome
years been cultivating chemifty with
a pro-
* Med. Eff. Eff. on the Poifon of Lead.
Rev. Mr. Milner, A. M. Fellow of
Queen's College.
( 374 )
a proper degree of enthufiafm, and
he has fucceeded in reducing red
lead by means of inflammable air in
the following manner. To one end
of a glass tube, into the middle of
which fome red lead had been put,
an empty bladder was tied; to the
other end a bladder full of inflam-
mable air, obtained from a folution
of iron in the acid of vitriol, was
faſtened very cloſe: that part of the
tube, in which the red lead was
principally lodged, being heated al-
moſt red hot, by being held over a
finall crucible full of burning char-
coal, the inflammable air was preſſed
out of the bladder; at its firft paffage
through the tube the red lead be-
came brown, as if it had been mixed
with fome oleaginous particles; and by
preffing the bladders alternately for
a fhort
(375)
a fhort ſpace of time, the red lead
was reduced into fmall globules of
lead; the quantity of inflammable
air was fenfibly diminiſhed, a part
it having been abforbed by the red
lead when it became a metal.
of
Occafion was taken in another
place to remark, the inflammable
air, as a conſtituent part of com-
buftible bodies, bore a great reſem-
blance to phlogiſton*, and a doubt
alſo has been expreffed, whether the
phlogiston of metallic fubftances be
not an elaſtic inflammable fluid; this
experiment, in which lead is reduced
by abſorbing inflammable air, tends
very much to firengthen that hypo-
thefis, and I doubt not we fhall fee
reafon to admit it without heſitation,
when the fubject has been more in-
* Vol. II. p. 33T.
veſtigated
( 376 )
veftigated; at prefent I do not
know whether it has been proved
that the whole of any definite quan-
tity of inflammable air can be ab-
forbed by a metallic earth; nor, if
it cannot, what the nature of the
remainder is: but the removal of
theſe, and other doubts, will be beft
accompliſhed by the ability of him,
to whom we owe the firſt ſuggeſtion
of the phlogifton of metallic fub-
ſtances being an inflammable air,
END OF VOL. III
1
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