COMPOUND ENGINES.
T,RAWNSLATED FROX THE FRENCH
A. MALLET.
NEW YORK:
D. VAN NOSTRAND, PUBLISHER,
23 MURRAY AND 27 WARREN STREET.
1874.




Entered according to Act of Congress in the year 1874, by
D. VAN NOSTRAND,
in the Office of the Librarian of Congress at Washington.




COMPOUND ENGINES.
We devote a few pages to the history of
Compound Engines; a history heretofore
little known, bat which we are able to make
complete by means of documents that enter
into minute details, and which contain matter instructive and interesting, while they
shed light upon subjects heretofore obscure.
The idea of employing the expansive
power of steam is generally attributed to
James Watt. This is shown by the evidence of a patent of Jan. 5, 1769, No. 913.
The process consisted in arresting the introduction of steam a little before the termination of the stroke of the piston, thus reducing the pressure at the moment of the
reverse stroke; it was not until sometime
after that it was perceived that a certain
quantity of steam was thus economized.
Jonathan Hornblower, who built the
Newcomen engines, patented the use of two




4
cylinders to effect the expansion, on the 13th
July, 1781, No. 1298. He said that he employed the steam after its action in the first
cylinder in order to employ it in the second
expansively.
Here is the original:' I use two vessels in which the steam is
to act, and which in other steam engines
are generally called cylinders.
"I employ the steam  after it has acted
on the first vessel to operate a second time
on the other, by permitting it to expand itself, which I do by connecting the vessels
together and forming proper channels and
apertures, whereby the steam shall occasionally go in and out of the said vessels."
Hornblower's engine met with small success. As it used steam at low pressure it
had but a limited expansive power, and the
advantages became of no account; rather
they became negative on account of the resistances due to the use of two pistons. Besides, he could not use his engine without
borrowing most of the parts of Watt's engine, such as the separate condenser, etc.
So Hornblower got by means of his inven



5
tion only the enmity of the friends of Watt,
who accused him of indirect plagiarism, and
created a bad reputation for him, of which
traces are found in the early histories of the
steam engine. At this time the use of two
cylinders turned out unsuccessful.
But when higher pressure was employed,
Woolf did for the engines of Trevithick,
Evans, and others, what Hornblower had
done for those of Watt; he applied to them
the principle of the double cylinder. As
he could make use of high pressure, there
was promise of success for the invention,
and it did succeed, so that he has given his
name to engines having two cylinders.
Woolf's patent was taken out in 1804.
It contained, as has often been remarked,
erroneous notions about the expansive power
of steam.
The fact that contributed to the success
of Woolf engines, was that although the
expansion was not sufficient to yield much
advantage over ordinary engines, the division of the work of the steam between
the two pistons diminished the differences
in pressure and the loss of -steam. This




was an important matter in the early
constructions. Engines of this kind need
little repair. WVe could mention two instances in an industrial centre in Normandy, of engines with two cylinders, which
have been in action for nearly fifty years.
In 1805, Willis Earle took out a patent
for engines composed of a large and small
cylinder superposed, with two pistons mounted on the same rod, a device frequently repeated since that time.
The first WToolf engine was set up in a
London brewery. Afterwards Hall made a
large number. In 1815 they were introduced into France by Edwards, and they
rapidly came into use, without much change
in construction. Edwards' engine of 1817
differs hardly at all, even in details, from
those that are to-day put up in some of the
manufacturing towns. In 1820 the English
engineers, Aitken and Steel, built engines
with three cylinders, two small and one
large. Notice of these engines appears in
various works, especially in that of R. Stuart.
In 1824 Joseph Eve patented a compound
engine, in which the steam, after acting in




7
a high-pressure engine, passed into a lowpressure engine, where it acted expansively.
He employed rotary engines. Hlere was
the first idea of a mode of action different
from that of Woolf's engines.
In 1834 Ernest Wolff (a German, we
infer, from his name) took out a patent (No.
6,600) of an engine described as compound,
as nowadays constructed, which indicates
the possibility of modifying existing engines
so as to adapt them to the new mode of action.
This patent is very interesting, and it is
singular that English authorities hardly refer to it.
It is certain that compound engines with
two cylinders and intermediate reservoir, to
which the name of Woolf has been given,
though they have not the same mode of action, should be called "' WVolff engines."
We give the essential part of this patent.
" The invention consists of the combination
of two or more engines, each complete in
all its parts, and so disposed that while the
first receives steam at one, two, or more
atmospheres of pressure, the next engine is
moved by the steam that escapes from the




8
first. In the last engine the steam is condensed in the ordinary way, or escapes into
the atmosphere. The work supplied by the
several engines is applied to the same shaft,
or to several combined, or to independent
shafts.
-" As in steam vessels and other applications, two conjoined engines are generally
employed.  The present invention is especially adapted for this purpose, as it presents economic advantages; as it reduces
the expense of the apparatus without increasing its complication.
" It is sometimes useful to have between
the cylinders an intermediate reservoir to
regulate the pressure; this may be placed
with advantage at the base of the chimney,
so as to maintain or raise the temperature
and the pressure of the steam in its passage
from one cylinder to the other. Indeed, if
necessary, the heat may be supplied by a
special fire-box.
" It is often necessary to employ a special
pipe with a stopcock to admit the steam
from the boiler to an intermediate reservoir
in order to give to the machine the power




9
of starting any crank.  This direct introduction may be employed to increase for a
time the power of the engine."
The writer then explains a method of
modifying old engines by adding to a highpressure engine a low-pressure cylinder;
or, in the case of a marine engine, by substituting for one of the low-pressure
cylinders a high-pressure cylinder.
The drawing annexed to the patent shows
a pair of marine beam-engines.
In 1837, William  Gilman patented an
engine consisting of two cylinders placed
one on the other, one of them having an
annular Piston with a single cut-off, with
multiple ports disconnecting the two cylinders. This disposition has been often reproduced, and is frequently employed nowadays, especially in Sweden. Gilman also
describes an engine of three cylinders in
which the steam acts in succession.
In 1837, Jonathan Dickson patented (No.
7,439) engines in which the steam acts
successively by means of boilers with decreasing pressure, or parts of boilers constituting a compound boiler.  This contri



10
vance has also been made use of since the
time of the invention. In fact, it is nothing
more than Woolf's patent: for this proposes
to re-heat the intermediate reservoir by a
special fire-box, a process which constitutes
in a certain way a low-pressure boiler.
Dickson proposes the use of feed-pumps
to serve as guides to the piston cranks, and
to control the slide-valves of each engine
by the other engine.
In the same year James Slater patented
(No. 7,467) engines acting in the same way,
with an intermediate reservoir, employing a
low-pressure boiler. He describes a regulating valve designed to keep the steam
pressure at a fixed point, and also to start
the engines. This is nothing more than
Woolf's invention-the valve, perhaps, excepted.
The drawings annexed to the patent
show various applications, especially a pair
of marine beam-engines.
William Whitman, in 1839, patented an
engine in which the piston has a sheath on
one side only, so that the cylinder has two
different capacities.  The steam first acts




11
in the annular space, then expands into the
other portion of the cylinder. This disposition, applied with some success by the
inventor, has been frequently reproduced.
It is probably the simplest way of applying
the Woolf method of action.
In 1841, James Sims patented an engine
of two superposed cylinders, with pistons on
the same rod; with this special distinction,
that the bottom of the smaller piston is in
constant communication with the top of the
larger.
In 1842, Hinrik Zander took out a patent
(No. 9,516) of an engine, in which the steam
acts in the first cylinder expansively, to a
certain extent, then passes into two others
which are larger, and expands.  The three
cylinders are attached to the same shaft, so
that their motion may be as uniform as possible. The low-pressure cylinders are provided with jackets which contain the steam
from the boiler. Zander describes intermediate reservoirs, and proposes to introduce into them, or into a communicating
pipe supplying their place, a float-valve to
allow the escape of condensed water.




12
In his drawings is represented a disposition in which the crank of an oscillating
high-pressure cylinder, placed obliquely, is
attached to the crank of a marine beam
engine. This engineer (probably of Holland) seems, according to documents which
we have found, to have built some marine
engines on this plan.
Octavius Henry Smith patented, in 1844,
an engine acting on the Woolfian principle,
consisting of a high-pressure and a lowpressure cylinder, both oscillating and
having their rods attached to the same
crank. The Cricket Engine, referred to in
Bramwell's memoir, is of this kind.  A
complete description will be found in the
" Practical Mechanic and Engineer's Magazine," 1847. Afterwards, we find many
patents of expansion engines. We mention
only those of Perkins, 1844; McNaught,
1845, which modified old engines by the
addition of a high-pressure cylinder; of
Thomas Craddock, 1852; Daniel Adamson
and Leonard Cooper, 1852, which superheated the steam in its passage from the
high to the low-pressure cylinder, by means




13
of tubes set in the smoke-box of a tubular
boiler.
We shall not go further in our examination of these patents. It is perceived that,
since 1852, all the essential elements of the
action of steam by expansion, in separate
cylinders, have been pointed out, and that
there remains nothing to be invented, even
in perfecting details. We shall look further
back for applications.
The Cricket Engine was built in 1847, by
Joyce & Co., of Greenwich. It exploded
the same year.  Bramwell speaks of a
boat built at about the same time by
Spiller, in which was placed an engine,
consisting of a low and high-pressure cylinder. We have found no document concerning it.
According to the authority of "Zeitschrift
des Oster Ing. and Arch.," 1867, M. Roetgen
of Rotterdam has built engines, since 1840,
composed of cylinders inclined towards each
other, and acting on the same pair of cranks,
the same steam being successively used in
the two cylinders. These engines were put




14
into the boats Etizabeth, Stadt Magdeburgh, IKron-Prinz Paul Friedrich.
We do not regard the date 1840 as exact.
If, as is probably the case, these engines
are those made according to the plans of
Zander, they were evidently built after his
patent of 1842.
The journal "Engineering " of Sept. 9,
1870, contains a description and drawing
of an engine built in 1848 by the Sterkerader IEIiitte for the Rhine boat Kron-Prinz
von  Preussen.   This engine had  two
cylinders one 0',508 in  diameter, and
0",800 long; the other 0',914 in diameter, and 0,914 in length.  Each acted
on a crank; the two cranks were connected
so that the effect was the same as if the
cylinders acted at righlt angles upon the
cranks, while the angle between the axes
was 130~. There was no special intermediate reservoir.  The connecting-pipe
Om,254 in diameter, acted in its stead.
There were no steam jackets, and, as no
precaution was taken to prevent the condensation of steam in its passage from one




15
cylinder to the other, economical results
could not be expected.
Still it is a fact that Feyenoord's works
at Rotterdam, where these engines were
first constructed, have never given them
up.  We ourselves saw at Rotterdam in
1860 a steamboat of 70 h. p. nominal, the
Wilhelm II., which had served as a pleasure boat for the King of Holland. The
engine, with low-pressure cylinder, had
been modified by the addition of a highpressure cylinder inclined to the other,
acting on the same crank, the same steam
working successively in the cylinders.
It would be unjust to omit mention of
Carillon, a Paris builder, who succeeded
(1842) in making a low-pressure engine
work with the discharged steam of one at
high pressure. This was set up at the St.
Louis Glass Works. The essay seems not
to have been repeated; being abandoned,.
we think, because of the failure of a surface condenser.
In 1852, James Samuel applied the prin-;
ciple of continuous expansion to locomotive
engines. This consists of a simultaneous




16
action of steam upon the two pistons. Suppose two pistons whose rods act at right
angles to the crank. The steam works at
full pressure during half the stroke of the
first. At this moment admission ceases,
and the first cylinder is put into communication with the second while its piston is
at the beginning of its stroke. Expansion
occurs simultaneously in the two cylinders
until near the end of the stroke of the first,
then in the second, only till nearly the end
of its stroke.
This system, related to that of Milner,
mentioned in Bramwell's memoir, has been
again taken up by Stewart & Nicholson,
and applied in the tugs on the Thames.
Though simple, it has the disadvantage of
not avoiding great depression of temperature as well as those of Woolf & Wolff,
since the two cylinders communicate with
the discharge ports or the condenser.
The experiments of Samuel, reported in
the "Memoirs of the Institution of Mechanical Engineers," 1852, were made on a
freight and a passenger engine on the
Eastern Counties Railway.  In the first




17
there were two equal cylinders; in the
second the larger cylinder had a section
twice as large as that of the smaller.
Though the results seemed quite favorable,
the essays were abandoned until the time
when they were again resumed by Stewart
& Nicholson. This is inferior to the other
kinds of compound engine.
The first noted applications of doublecylinder engines were made at Glasgow, in
1856, by Randolph & Elder. A little after,
Rowan & Horton constructed three cylinder
engines; one high-pressure feeding two
others.  There were 6 cylinders in the
machine. The steam was supplied at a
pressure of 8 atmospheres by boilers of a
special form.
One of these engines, according to Rankine, should not consume more than 0,500 k.
of fuel per horse power hourly. This would
seem doubtful; but it would be useless to
discuss the point, for the engines have not
stood the test of service. The boilers are
rapidly destroyed, and the construction is
too complicated. The condensers were surface condensers of a particular pattern.




18
Rowan & Horton put one of their engines
into L'Actif, a French vessel.
In 1859, Humphreys & Tennant, of Deptford, built for the Peninsular and Oriental
Company Woolf engines with moderate
tensions.  These engines, set up in the
steamers Poonah, Mooltan, Carnatic, Baroda, Delhi, etc., at first gave good results.
The pressure was 25 lbs., with surface condensation. The cylinders of the Mooltan
were 96 and 46 in. in diameter, with a
length of 3 ft. Consumption was 21 lbs.
per horse power. The good results were
not permanent, especially in matters of
detail.
All these have been replaced by single
engines built by Humphreys & Tennant.
In 1861, Normand changed to the Wolff
the engine of the small steamer Le Furet
built by Penn. The engine worked at 6
atmospheres with intermediate reservoir,
re-heating, and monhycdric condensation.
The results were excellent. Afterwards
Normand altered in the same way the engines of the Eclair, the Albert, etc., and
still constructs the same kind of engines.




19
The Imperial Marine made essays moderately successful with three cylinders. The
expansion was not great enough, the cylinders being of the same diameter, so that
the economic advantage was not important.
But the principle seems natural, and the
English Admiralty is at present changing
the engines of the ship Jumna.
Escher, Wyss & Co., of Zurich, have
built, from the plans of their engineer,
Murray Jackson, marine engines with a
low and a high-pressure cylinder, set side
by side and acting perpendicularly to the
cranks. One of these engines was exhibited
at Paris in 1861, but it was out of sight
under a shed. They have no special intermediate reservoir, the connecting pipe of
the cylinders acting in its place. This firm
have constructed a large number for the
Swiss and Italian lakes, for the Danube,
Rhine, ana other rivers. Their engines are
of the Woolf system. One with four cylinders was exhibited at London in 1862; it is
now upon a boat upon Lake Lucerne.
The compound marine Wolff engine is
at present built in many English shops;




20
though some maintain the Woolf type, with
superposed cylinders. In France all engines are of the first kind.
II. We now consider the method of action in compound engines, beginning with
those of Woolf.
In this system the pistons almost always
move parallel and in the same direction,
although engines with opposing cranks have
been constructed (Randolph & Elder; Bondier Freres, of Rouen; Carret, Marshall &
Co.) in order to have more direct connection
between the cylinders. We suppose that
the cylinders have the same length.
The steam acts directly upon the first piston, then expansively; and when the small
piston is at the end of its stroke, the connection with the large begins, so that the
space under the action of steam at any instant is composed of a fraction of each cylinder, the fractions having an inverse ratio.
We calculate the volume for each period
of the stroke, and find the corresponding
pressure by Mariotte's law. Let S and s
represent the areas of the pistons, I the
stroke when the pistons are at a distance z




21
from the beginning of the stroke. The remaining volume in the small cylinder is
s(l-z), the volume of steam in the large cylinder is Sz, hence the total volume occupied
by the steam is
s (1-z)+S z
or
s Is-s z+-Sz = sl+ (S-S)z.
If P' is the pressure at the end of the
strokes of the small piston, the pressure at
any point between the two pistons is
PI s I
x     1 + (S-s) z
By giving to z a number of values, the
curve of expansion may be constructed.
P' is the boiler pressure if there is no
expansion in the small cylinder; otherwise,
from P' we deduct P' from the pressure P
in the boiler by the relation
Pn =p    _  hn being the expansion in the first cylinder. Denoting by v and V the volumes of
the cylinders, by mn the total expansion, we
have for the expenditure of steam
V,
q




22
The work of the volume q of steam is
T-=qP( 1 +2,3026 log.)
an expression which does not contain v, i. e.,
the work does not depend on the volume of
the small cylinder, but only on the volume
q of steam  expended, and upon the di.
mensions of the large cylinder and the initial pressure.
Theoretically, then, the work is the same
as if there were no small cylinder, and the
volume of steam introduced into it is directly expended in the large cylinder. Should
we therefore conclude, as most persons do,
that the small piston does no work, and
that it is merely a distributor? This would
be utterly erroneous; the work of the lowpressure cylinder alone, would be represented by V and by a certain mean pressure 7r.
Then denoting by p the mean pressure in
the small cylinder, byp' the mean pressure
between the two pistons, we have
T =vp-vip' - Vp.
p v +-p' (V-v) = V r.'  _ a 1  +    (P-_0,




23
a value always larger than p'; hence the
total work is always greater than that of
the large cylinder. 
V
From  the expression msn -__n we have
V    m
= —, which determines the proportion
between the cylinders for a given total expansion and introduction into the first cyl-.
inder.
We observe that in order to have V = v,.
or equal cylinders, we must have n= —nz; and
the second cylinder would be useless, so
that the two cylinders could be practically
equal in Woolf's engine. The same is true
in the Wolff engine, as will appear.
The following table shows the dimensions of the large cylinder (those of the
small being equal to unity) for given total
expansions and admissions into the small
cylinder:




24
Admissions
to the        0.3.     0.4.      0.5.
small cylinder.
r5   1.5        2         2.5
Total expansion 15   4.       6         7.6.20   6         8        10.
Admissions
to the      0.6.   0.7.    0.8.    0.9.
small cylinder.
r 5   3    3.5  r4        4.5
Totalx     10   6    7.  e 8          9
Total expanion 15   9   10.5    12  13.5
{20  10   14.       16    18
The ratio 5 is not exceeded in practice
it being better, for large expansions, to in-,crease the expansion for the first cylinder.
We have so far supposed that there was
no dead space, a condition never realized.'This space is composed of two parts; one,
the space between the small piston and the'bottom of the cylinder at the end of its:stroke and the port of the small cylinder,,the other composed of the -interior capacity




25
of the small slide valve, of the connecting
pipe between the valve boxes (we suppose
each cylinder has its special distributor), of
the valve box of the large cylinder, of the
port of the large cylinder, and finally of the
free space between the large piston and the
bottori of the cylinder at the end of its
stroke.
The first space contains, at the end of
the stroke, an amount of steam (P') of the
final tension of the stroke of the small piston; but the second space contains steam
of a tension (P"') corresponding to that existing at the end of the stroke of the large
piston; and it should be filled with steam
of the tension P'.
A communication is established between
the two cylinders; the tension diminishes
because of the dead space not corresponding to the displacement of the pistons; and
the mean pressure on the large piston is
considerably diminished.
In the old two-cylinder engines the dead
space is considerable, sometimes exceeding
one-third the volume of the small cylinder;
but it has been diminished by a suitable




26
disposition of slide-valves; and it can be
prevented in a certain measure by causing
compression at the end of the stroke of the
large piston.
If the dead space is a fraction I of the
volume?v of the small cylinder, the pressure.
at the beginning of the stroke of the large
piston, instead of being  h will be  ~+  V.
For example, for k =  3, it would be
13 = 0. 75,
instead of 1.
If the initial pressure in the large cylinP' v
der, instead of P' is v +  v, at the end of.k
-its stroke, when the volume is V + -, the
final tension will be
P'v    v-         P' v
+     v     v+ -   v
instead of-V  The ratio of the two vo
instead of.  The ratio of the two vol



27
I
umes is 1+  v. If+v   0.2 and k   3,
V k
the ratio is 0.98.
The final tension is not sensibly modified
because the ratio of the volume of the
cylinders diminishes the effect of the dead
space; that is, because the steam contained
in this dead space expands during the
stroke and tends to restore the tension.
For a better understanding of the subject,
and to show the action of the engines, we
reproduce in Figs. 1 and 2 the diagrams of
indicator of a large Woolf beam engine,
built by Slawecki, an engineer at tRoulri,
who subjected the engine to interesting
dynamometric experiments.
Fig. I shows the curves of the two cylinders to the same scale and with the same
atmospheric line.  We observe that the
counter-pressure  of the  small cylinder
corresponds very exactly to the pressure
upon the large piston, showing that the
resistances in the passages between the two
cylinders are so diminished as to be almost
insensible.




28
That the two curves coincide at one point,
is due to the fact that they were taken at
FIG. 1.
t9 a
the top of the cylinder, where the real re



29
presentation of the action of the sacne steam
upon each'piston is not given.
The effect of dead space is shown by the
difference between the final pressure in the
small cylinder and the initial pressure in
the large. In this case the difference is one
and a half atmospheres.
In order to compare the action of the
Woolf with that of an ordinary engine with
a single cylinder, we show in Fig. 2 two
curves to the same vertical scale for ordinary pressures, but with abscissas to
scales proportional to the volumes of
the cylinders.  As the two areas coincide
upon the portion marked with vertical
hatchings, this portion has been transferred
to an equal area hatched horizontally. The
curve of work of the steam acting on a
single cylinder with the same expansion as
in the engine with two cylinders is given;
and the small portion of the area corresponding to the work of the small cylinder beyond
curve is shown within it.
It is seen that the final pressure is exactly the same in the two systems, except
that there is a defect of area of work in




FIG. 2.
4 4
II
7           ie -I tl                                            ________                                _      _    _    _        _ _A/mo     h
I 1                   2                                3     4                  5                  6                   7                  8                  9    y 18flnA I
I                                     3                  4                   5                  6                  7?                 8                   9  7o~lUm~PS  7




31
Woolf's engine corresponding to the loss
due to dead space. Calculating the area of
this portion, we find the loss due to the
use of two cylinders to be nearly 15 per
cent.
The majority of authorities rest here, and
take this result as a text for condemning
the compound-engine, at least in principle.
We shall see that the physical loss in the
action of expansive engines with one cylinder far surpasses that of the Woolf, a loss in
some sort apparent, and depending upon a
simply geometric cause.
This would be the place to examine the
causes of the superiority of this engine due
to expansion; but as this superiority is
common, in theory at least, to all doublecylinder engines, we shall consider the
question after an examination of the second
kind of engines.
We close with this remark concerning
Woolf engines: if each cylinder is provided
with a special distribution, it is not necessary that there should be a mathematical
correspondence of exhaust port of the first
cylinder with the admission port of the




32
second. The existence of dead spaces permits separation by a certain interval; while
near the dead-points the angular displacement of the crank corresponds to a very
small linear displacement of the piston.
[HIence if each cylinder acts upon a special
crank, the two cranks may be set at an
angle of 45 deg. to 135 deg., acccording as
the pistons are to move in the same or
opposite directions. This disposition which
facilitates the passage of the dead-points is
sometimes employed, as appears in Bramwell's memoir.
III. In the second system of engines,
which should be called Wolff engines, the
second cylinder is not supplied directly by
the first, but by an intermediate reservoir
of such dimensions that the pressure within
it may be regarded as nearly constant, being in some sort an engine with graduated
pressure.
Denoting by P the pressure in the boiler,
supposed equal to pressure upon entering
the first cylinder, and by P' the pressure
in the intermediate reservoir, due in the
first place to direct introduction of the




33
steam from the boiler, and controlled by a
safety valve; by P" the resisting pressure
at the discharge port or at the condenser;
then, if the expansion n in the first cylinder
is such that the final pressure in this cylinder is P', or differs from  it but little (v
being the volume of the small cylinder, and
q the volume of the steam admitted), we
have'P'   q    1.
P.v    A
The second cylinder receives all the
steam from the boiler at the pressure P".
_    P
Then         - p, -n; m being the total
V    m
expansion, hence v     n -    and the ratio
of the volumes of the cylinders is the same
as in the first system. But the large cylinder, instead of receiving the steam during
the entire stroke, receives it only while a
fraction equal to the expansion n' corresponds to the decrease of the pressure from
P
P' to P";       n and since --- n and
p     /  P
_   =n-    n! m.
n   P/




34'The total expansion is equal to the product
of the partial expansions, and the expansion
in the second cylinder is equal to the ratio
of the volumes of the two cylinders. We
see that if one should make the two cylinders equal in an engine of this kind, there
would be no expansion in the second cylinder. The engine might act if there were a
notable difference between P' and P", but
the whole possible expansion would not be
utilized, and the system would have no raison cl'etre.
One of the advantages of this arrangement is that the dead spaces are not hurtful, as they are actually utilized by enlarging them.
The work of the steam in the first cylinder is
T=q.P(l+elog V) v.
that in the second is
T-qP' (l-log    )-PadV.
Taking the sum for the total work, and
substituting




35
~ q= __   P
we have
T —  (P (1+e logn-1+l+  log n- -P/),
V
T= _P (1 + e log m)-P" m
-P?+ elog m) -V P//
=-qP(+elog - V )P"
This expression represents the work in
the large cylinder of the quantity of steam
at tension P, expanded from volume q to
the volume V.
The principle stated concerning Woolf's
engine also holds as to the action of this
kind; that is, the work is the same as if
the large cylinder were the only one, and
the steam admitted to the small cylinder
were directly introduced into the large, and
expanded in the ratio of the total expansion.
In this kind of engine the work of the
two cylinders is regulated as much as possible. Equating the expressions of work
given above, we find after proper substitutions




P(P(1+elo  1 )        _V (-P1 (l+e log )-,
and substituting for P' its value —,
P (1 + elog n)-P
V            n1
v   P(1 - e log ~n)_p,
m
-  e log n
P (1;+- e log n') -P"'This expression gives the ratio- for
V
known expansions n and n', for we always
have m -    nr'.
Remembering that
P          P
P= P and   P  //
n          9in
we have
V    P' e log n   log n
v   P// e log n/    n'
and for n - n'
- n
a relation already known.
In Woolf's engine the extreme difference




37
of temperatures in the small cylinder is
larger than  in  the engine with  inter-mediate reservoir. Hiere is a theoretic inferiority, at least for engines of slow action
in which the decrease of temperature
due to the diminution of tension is noteworthy. HIence, as we shall see, the use of
an envelope of steam is in this case more necessary.
If the engine with reservoir has a real
advantage over that of Woolf, it has, on the
other hand, the inconvenience of requiring
for considerable expansions, that the admission be early cut off in each cylinder: since
for a total expansion of 10 volumes the expansion should occupy ~ in one cylinder, ~
in the other, or    r in each, if expansions
in both are equal; and we know that ordinary distribution does not favor small introductions.
Generally a fixed expansion is imposed
upon the large cylinder; and the small
cylinder is provided with a special apparatus,
with variable cut-off to reduce admission as
desired. It is difficult, however, to effect
large expansions, and too great expansion in




38
the large cylinder produces some of the
disadvantages of the single cylinder. It
would be better, in this case, to employ
multiple expansions and several successive
cylinders, as has often been proposed.
We shall now investigate the causes of
the physical superiority in the action of
compound engines over those with a single
cylinder.
These causes are two in number:  The
first, which is common to all engines of this
class, is due to the fact that the difference
of extreme temperatures in each cylinder is
less, and that the interior condensation is
much diminished. The second, which is
peculiar to engines with an intermediate
reservoir, is due to the partial removal of
the water from the steam which held it in
suspension at the time of its leaving the
first cylinder; so that the water does not
pass, in a liquid form at least, to the second
cylinder.
For the better comprehension of these
effects, it is necessary first to examine what
takes place in single-cylinder engines. Suppose an engine of this kind acting expan



39
sively; the steam is admitted during, say
one-fifth of the stroke. Then the piston
moves by virtue of the expansion, and
the pressure diminishes in a certain ratio
with the increase of volume, until the
end of the stroke. As the temperature of
the steam diminishes with its pressure, a
contraction takes place in consequence of
the cooling, which acts at the same time
with the expansion to diminish the pressure; and we perceive that if the steam receives no heat during its expansion, the
pressures will diminish more rapidly than
by Mariotte's law. But, on investigation of
the action of expanding engines without
cylinder envelope, we find a different condition of things. We have taken a number
of indicator diagrams from a non-condensing engine, into which admission took place
only during very small fractions of the
stroke, varying from  o to 8. Besides, the
actual expansions were much less because
of dead space; the correction reducing the
apparent expansions from 40, 20, 13.33, 10
and 8 to 14, 10.5, 8.04, 7, 6 volumes.
The figure (3) shows the diagram from




40
an engine with actual expansion of 14 volumes. The initial absolute pressure being
2.75 atmospheres, the tension at the end of
the stroke, by Mariotte's law, should be
considerably below the atmospheric pressure. The diagram shows the contrary.
The pressure, which decreases rapidly near
the post, afterwards approaches the horizontal line, and at the end of the stroke is
considerably above the atmospheric line.
This is due to the vaporization of the water
in the cylinder during the period of expansion, which furnishes a supplement of steam
whose tension is added to the primitive tension.
At first it seems that it is an advantage
that the work obtained is greater than that
due to Mariotte's law; but we must count
the cost, and it is easy to show that it costs
as much or more than the work of full
pressure during the entire stroke, so that
all advantage of the expansion is lost.
By calculation of the area of the curve
and of the mean ordinate, we shall find the
mean effective tension of the steam to be
0.236 kil. per square centimetre. The cyl



FIGS. 3 AND 4.
Atmosph.Line
Atmospk. Lite




42
inder has a diameter of 0.200 m., a stroke
of 0.40 m., 30 strokes per minute; the
work on the piston is 29.2 kilogrammetres.
The volume of steam in the cylinder at the
instant of closing of the admission port,
dead space included, is 0.9421. This weighs
(at a tension of 2.75 at.) 1.50 gr. per litre;
that is, 1. 163 gr. for 30 strokes per minute,
corresponding to 4,547 per hour, or 11.65
H. P. of sensible steam acting on the
piston.
If we now take a volume corresponding
to.r- of the stroke, and, assuming that the
steam is in a saturated condition in the cylinder, apply to this volume the weight per
litre corresponding to the observed pressure, we find at this moment in the cylinder
a weight not of 1,263 gr., but of 1,410 gr.;
at the middle of the course it is 4,837 gr. At
the end it is still less, but at this point observation becomes more difficult because the
pressure comes near the atmospheric line.
We assume the figures 4,837 gr., which
correspond to a sensible expenditure of 47
kilog. of steam  per HI. P., hourly; i. e., 4
times the amount found above.




43
Referring to figure answering to the admission for the whole stroke, we find that
the mean ordinate of mean effective pressure is 1.56 kil., giving for 30 revolutions a
work on the piston of 196 kilograinmetres,
or 2,615 H. P. The volume of steam which
fills the cylinder' at the end of the stroke is
12.561.; which, at a pressure of 2.95 atmospheres, gives 18.84 gr., or 67.824 kil. hourly, or 26 kil. per El. P.
As there can be no other steam in the
cylinder, we must conclude that the engine
uses less at full pressure than when acting
with full expansion, a fact long ago verified.
The presence of the great quantity of
steam in the cylinder, can be explained,
only as due to vaporization during the period of expansion of the water contained in
the cylinder, which is caused by diminution
of pressure, and at the expense of the heat;
of the metal. But from what source does
this water come? In the case under consideration the water was supplied by a tubular boiler; but the engine went very
slow and did very little work.
As the dimensions of the boiler correspond



44
ed to a performance 15 or 20 times as great,
it is difficult to admit that any considerable
portion of the water was held in suspension
in the steam. It was almost entirely due
to the condensation at the- admission
port. The steam meets the surfaces, walls:
and ends of the cylinder, the piston and the
rod, all of which are at a lower temperature, and partly condenses, while it raises
the temperature of the metal. To raise 10
kilog. of metal 10 deg. requires 10 X 10 X
0.15, or 15 units of heat, answering to al
condensation of about 30 grammes of steam.
Hence, at the beginning of the stroke there
is a certain quantity of water; it is this
which vaporizes as soon as the pressure at
the admission port diminishes, by absorbing the heat of the walls of the cylinder
and that of the piston, a heat which is lost
by escape or by transfer to the condenser.;
The cooled metal then demands from the
steam just arrived from the boiler a fresh:
quantity of heat, acting as an agent to exr-,change between boiler and condenser. This'
explains the fact often noticed, that in con-~
densing engines, having cylinders without




45
jackets, it is more difficult to effect a vacuum
with complete expansion than with full
steam.
It is to be observed that the elevation of
the temperature of the walls of the cylinder
by condensation does, not take place instantaneously, any more than does the vaporization that attends expansion. Time has
its part in the phenomenon. In engines of
slow action the loss of heat is much greater
than in those of more rapid movement.
The engine in our own experiments was
under the most unfavorable conditions; acting without condensation, at full expansion,
slowly, and at a low pressure.
The office of steam jackets is to keep the
walls of the cylinder at a constant temperature, so as to prevent the presence of water
in the cylinder and the resulting inconveniences. A certain quantity of heat is lost,
corresponding to the condensation in the
jacket; but as the pressure in the jacket,
does not vary, this condensed steam will remain in the condition of water, or will be
expelled by the clearing valves; it will not
pass back into the state of vapor while ab



sorbing the heat, as would be the case if it
had been condensed in the cylinder. This
is the true statement of the action of jackets: they maintain the heat in the cylinder
and cause condensation to take place in the
jacket where the pressure is constant, and
not in the cylinder where it is variable.
The jacket does not always prevent the
formation of water within the body of
steam, because of very prolonged expansions due to cooling and dilatation. We
shall find it possible to avoid these consequences.
The following observations are of interest:
(1) We note the little efficacy in the action of jackets of wood, felt, polished brass,
etc., which resist only cooling from without.
(2) It is easy to show that little would
be effected by replacing the steam in the
jacket by the heated gases of combustion,
as has been attempted in some engines
(sometimes the interior cylinders of locomotive engines are placed in the smoke
chest).




47
A cubic metre of steam at 5 atmospheres
weighs 2,600 kil., and by condensation may
lose 500 heat units per kilogramme, or
1,300 per cubic metre. A cubic metre of
gas from combustion, at a temperature of
350 deg. represents 0.66 kil. giving 200 X
0.25 X 0.66 —33 heat units.
To replace a layer of steam a eentimetre
in thickness would require a layer 40 centimetres thick, of heated gas, (assuming that
the conductibility is perfect), or 40 square
metres to replace a square metre of heated
steam.
(3) In the old engines the steam from
the boiler circulated in the jacket before
entering the cylinder.  It is easy to see
that this would cause steam to pass into the
cylinders containing water in suspension,
which would cause a clear loss of heat in
case of expansion; then this water would
remain in the jacket without disadvantage.
A special pipe should always be used
through which to pass the steam into the
jackets.
What has been said regarding the jackets applies equally to the cylinder ends and




48
to the pistons. The importance of regarding the latter is great in engines of short
stroke, in which the diameter is 2- times or
more than the stroke. In these engines
the ends are always heated; and pistons
are heated by means of grooved rods and
other devices.
Nowadays cylinders and their jackets are
generally of the same coating, in order to
avoid complex and delicate adjustments.
Hence serious difficulties in construction.
Perkins, in the engines of the steamer Filga, substituted for the jacket a serpentine
iron tube sunk into the cylinder. In this
tube the steam circulates. This compels
an increased thickness of the cylinder. But
the weight need not be much greater than
with a jacket, and the construction is easier.
We return to two-cylinder engines. Notwithstanding the real efficacy of steam jack*ets, still it is certain that there is always
more or less condensation of water during
expansion. This is necessarily proportional
to the extreme differences of temperature to




49
which the cylinder is subjected, as well as
to the extent of cooling surfaces.
In double-cylinder engines, especially with
intermediate reservoir, this difference of temperature is reduced for each cylinder. If
we suppose a pressure of 5 atmospheres,
corresponding to 152 deg., an intermediate
pressure of 2, corresponding to 120 deg.,
and a final pressure of 0.50, corresponding
to 81 deg., the difference in the first cylinder will be 32 deg., in the second, 39 deg.
With a single cylinder the difference would
be 71 deg.
We shall find that the total condensation
will be considerably diminished.  Suppose
the ratio of volumes of the two cylinders to
be 2, 5, the first being 0.78, its total cooling
surface is 4.70. The volume of the large
cylinder being 0.78 X 2.5= —1.95, its cooling
surface is 8.86. We have then
4.7 X 32~+ 8.86 X 39=-495.
A single-cylinder engine of the same work
and the same expansion should have the
dimensions of the large cylinder. In this
case we have
8.86 X 71=629.




50
The advantage in favor of the double-cylinder engine is 21 per cent. It is so real
that, as mentioned before, jackets are sometimes dispensed with in compound engines,
when the expansions are not great. It is
possible also in engines with intermediate
reservoir, which have the special advantage,that the water held in suspension at
the time of leaving the first cylinder is deposited in the reservoir and does not pass
into the second cylinder. It would seem
that it always has been observed that the
intermediate reservoir produces much water,
for Zander, in his patent, mentions the use
of a float valve to discharge this water. The
intermediate heater vaporizes this water
and makes it do work again in the large
cylinder.
The following are, the conclusions which
we think can be drawn from our investigations:
(1) The usefulness of a steam envelope is
incontestable, being greater as the differences in temperature increase, so that jackets are more advantageous for condensing
than for non-condensing engines, for great




51
expansion than for slight, for single than
for double-cylinder engines. But when expansion is considerable, the jacket is not
sufficient.
(2) Engines of two cylinders have a decided superiority over those with one, so
that for moderate expansions, steam jackets
may be dispensed with.
(3) The compound engine, which we
have called the Wolff, has advantages over
the ordinary Woolf engine, because the
dead spaces have less influence, and because the steam  that has worked in the
first cylinder can be there separated from
the water, so as to work better in the second cylinder. Again, the small cylinder is
less exposed to interior cooling, and it is
less necessary to employ the steam jacket.
These facts seem  very simple, yet they
are often misconceived: For example, we
read in the work of a distinguished author,
as follows:  "The means by which economy of steam is attained, consist, while using
mean or high pressures, (1) in superheating
the steam; (2) in employing long expansions, either by Woolf's method, or directly.




52
This requires, all other things being equal,
less complicated apparatus, and it is considered efficient at least as regards the utilization of the steam. In land engines, where
space is of little account, some builders propose to make use of expansions of 0.95 (20
volumes). In all such cases the cylinders
have envelopes. But the use of jackets with
circulation of steam is to be avoided."
This was written in 1866. We think
that, in view of a great number of facts and
of the general use of the compound engine,
the author should modify his conclusions.
The Bulletin of the Industrial Scientific
Society of Marseilles (1873) contains this
note upon steam jackets, by Stapfer:
"Steam jackets are a costly addition,
which only apparently increase the power
of an engine. They seldom last more than
two years, unless with the greatest precaution. Indeed, there are few engines in
which they are not much obstructed. Of
course, I do not refer to locomotives whose
cylinders are inside the steam chest or in
the smoke box, but only to return-water
jackets. It is obvious that byplacing the




53
cylinder in an atmosphere of waste gases at
300 or 400 deg., a very appreciable quantity of heat can be utilized. But these are
conditions seldom realized, and they belong
rather to the construction of the boiler."
We can here only refer the reader to
what has been said above concerning the
real value of the direct action of the gases
of combustion. They can be turned to account only by the aid of considerable surfaces. Those of the cylinders and the intermediate reservoir are not sufficient.
The heat of the gases of combustion has
often been employed to reheat the steam in
its passage from one cylinder to the other.
Normand has made use of a tubular apparatus set in the smoke box. \ This was,applied to his first engines and is found
in his latest, as in the Ville de Brest and the:Belgrano.
Stapfer says that jackets use too much
steam; and to a certain extent without
useful result, by superheating the steam at
the end of its course in the large cylinder,
when it is about to pass to the condenser.
This objection has probably in some cases




54
caused the suppression of the jacket of the
large cylinder. Though the action of the
jacket may be very efficient in vaporizing
the water of condensation, especially on the
cylinder walls, it is of little effect in heating
the steam, the conductibility of which is
very feeble. If, then, there is a superheating of steam, it occurs only in immediate
proximity with the walls, and only when all
the water has been vaporized. This vaporization and the effect of the jacket are of no
account while the piston is driven by the
steam. That the loss should be appreciable particular conditions are necessary; for
example, that the escape should take place
during a considerable portion of the stroke.
In engines of rapid action, the transmission of heat would not be sufficiently rapid.
Stapfer seems to perceive this fact, for he
says:  "Steam jackets would be good for
engines of slow action, in which heating
takes place slowly."
The objection regarding the waste of
steam by the jacket, made even when it is
proven that this helps to avoid a greater
waste, holds true in a degree only. But it




55
is worth while to reduce it as much as possible. We think this can be done by employing the gases of combustion, not in
directly heating the cylinders, but in gen-.
erating steam to feed the jackets. The apparatus might consist of a small group of
tubes at the base of the chimney where a
portion of the water condensed in the jackets would collect, either by the action of its
own weight or by contrivances easily adjusted.
The water would always be the same,
and not coming into contact with impure
substances, it would remain free from the
obstructions.
The steam generated in this small boiler
heated by the gases of combustion would
serve only to heat the cylinders, and not at
all in the direct production of motive power;
s6 that it would be possible to supply the
heat necessary for the jackets without cost.
Attempts have been made to utilize the
heat held in the steam at its discharge from
the cylinder by vaporizing a liquid more
volatile than water, and to have this vapor
act upon a second piston. By this means




56
more work would be realized without employing much of the expansion of the first
cylinder.  These engines, invented by Dutrembley, who has made a great number of
them, are engines of graduated pressure
(pressions etagees). It is easy to show that
the same result is obtained more simply by
utilizing the expansion of the steam in snccessive cylinders.
Suppose a kilogralmme of steam leaves the
first cylinder and enters the ether condenser
at 80 deg. or at one-half an atmosphere.
This steam can supply 550 heat units and
will vaporize about 3.5 kil. of ether at 3
atmospheres of pressure, or 440 litres of
vapor. These cannot be in the ether condenser less than an atmosphere of resisting
pressure; for the boiling point of ether is
38 deg.; so that expansion cannot be more
than 3 atmospheres tol1.
The work of the ether cylinder will be
O.440 X 3 (1 + e log. 3)-1.32 X 1=-1.45.
If, instead of using the steam to vaporize
ether, expansion is effected in a.second cylinder, nearly up to the condenser pressure,




57
it could be raised front 0.5 to 0.2 or 2.5 volumes; even supposing the most unfavorable conditions, as a tetnsion of half an atmosphere at discharge from the first cylinder;
which would imply a previous considerable
expansion.
A kilogramme of steam at half an atmosphere, represents 3.200 me.; hence the
work would be
3.200 X 0.5 (1-e log. 2.5)-8 X 0.2 = 1.47.
The work is theoretically the same as that
with ether; but in fact it would be more
considerable, and it is obtained more simply,
without the help of a dangerous fluid, without cqmplicated vaporizers and condensers,
and other disadvantages. It is but a slight
advantage that the ether cylinder would
have a volume of 1.32, while that of the
compound engine has a volume of 8.
A disadvantage in the use of ether is, that
though the boiling point is low, its tension
in the condenser is high, so that what is
gained in one way is lost in another. Besides, its vapor has considerable density.
Combined vapor engines have given good




58
results when comparison was made with
engines in which.steam  has been badly
utilized. They gave splendid results when
their consumption was 1.50 kil.: per H. P.,
as compared with 2.25 to 2.50 kil. of steam
engines. Nowadays, a kilogramme per I.
P. is realized with much simpler means.
Still it would not be fair to forget that ether
engines have rendered important service by
familiarizing us with the use of surface condensers. The majority of these engines,
after the use of ether was given up, have
been worked as steam engines with the use
of ether vaporizers and condensers as surface condensers.
F. Our investigations naturally lead to
the question whether by increase of pressures and expansions indefinite improvements may be realized; or, as Siemens has
said in his report to the Institute of Meichanical Engineers, whether, in the course
of ten years, we may not hope for a reduction of 50 per cent. in consumption.
We must first say a few words of the
methods of determining the useful effect ot
our engines. It is hardly necessary to re



59
mark upon the superficial and crude nature
of the results generally given concerning
the performance of a steam engine, results
indicating the amount of fuel burned per
hour, the unit of work upon pistons and
cranks.
We often see the consumption indicated
with the minutest accuracy in figures containing two or three decimals; and this
without the slightest mention of the kind of
fuel employed, though it is well known that
the heating powers of combustibles vary
greatly, so that an engine can run more
economically with 2 kil. of one sort of fuel
than with 1.50 kil. of another. What value
have such reports?
Suppose the kind of fuel accurately stated; still the figure of consumption per H.
P. has no scientific value because it confounds in one estimate a set of distinct elements which should be separately examined,
as the amount of steam and its use, the
work of the generator and that of the engine.
This is clear. Take for example an engine that uses 10 kil. of steam per H. P.




60
This is supplied by a boiler set under very
bad conditions, vaporizing only 5 kilog. of
water per kilog. of fuel. The consumption
is 2 kil. hourly per H. P. Another engine
may use 20 kilog. of steam, but if it is fed
by a generator that very perfectly vaporizes 10 kilog. of water per kil. of fuel, the
gross result of consumption per H. P. will
also be 2 kilog.  There is no apparent difference between the two.
The careful examination of this question
is of great interest, for it leads to an important result: the conclusion that, if we give
to the better of the two engines the better
generator; or, if to the generator is attached
an engine that utilizes the steam in the best
manner, then, instead of 2 kilog., we should
have 1 kilog. of consumption, or 50 per cent.
economy.'That steam engines have been gradually.
brought to their present perfection, is due
to the minute and careful analysis of the
physical phenomena which convert the heat
of coal into a motor force. It is easy to indicate the necessity of the separate study of
the elements of the steam engine, but not




61
easy to represent this separation in practical experiments. But it is possible, in land
engines, to take a satisfactory account of
the interior action of the apparatus, both by
observation of the weight of fuel burned
and of water converted into steam, and by
measuring the work on the shaft by the
Prony brake and the work upon the piston
by the indicator. But in the case of great
marine engines, the weight of fuel and the
work upon the pistons are the only elements easily measured. Results must be
obtained by comparison or by appro ximation, somewhat coarse, it is true, but yet of
great interest, and with much probability of
correctness in them, because of the great
number of facts we have at hand.
In marine engines, the expenditure of
steam-and therefore the performance-is
generally estimated by what is termed the
weight of sensible steam in the cylinders;
that is, the weight as shown by the indicator diagrams. As we have seen, this indication is often illusory. Though in engines
in which the condensation in the cylinders
is limited by suitable conditions of action, it




62
may approach the real figure, so as to give
results accurate enough in practice, still, in
other cases, it gives results of no possible
value.
This weight of sensible steam in the cylinder, which we shall call P', differs from
the weight P' of water actually vaporized in
the boiler, because it does not take into account the loss of steam by leakages, condensations in the tubes or at the entrance
to the cylinder, by dead spaces, etc. But it
also differs from the weight p of steam theoretic$ly necessary for a given pressure
and expansion; because it takes into account the various restrictive elements of the
motor force, such as the reduction of pressure between the boiler and the cylinder,
the phases of distribution, lead, compression, actual expansion, obstruction, etc.
Hence, in general
P> P'>p.
Further on we shall find apparent exceptions, for which we should be prepared.
We shall first determine, for various
pressures and expansions, the theoretic




63
weight of the vapor p consumed hourly
to produce the work of a HI. P., on the piston.
The following table gives the values of p
for several kinds of marine engines. The
figures are theoretic, being obtained from
the formula for the work of steam. Only the
resisting pressure in the condenser, estimated at 2 metres of water, is taken into account. (See page 64.)
The figure illustrates the results graphically. (See Fig. 5, page 65.)
The weight P' of sensible steam in the
cylinders shown by the indicator, should be
more than the theoretic weight p, since the
steam loses in various ways during its work.
Of these losses, some are shown by the diagram, others are not sensible and introduce
so many errors into the results that they
are really not of practical use. They are
almost exact enough for engines in which
the condensation in the cylinders is a minimum. But they answer only when comparison is made of engines whose actions are
nearly identical. Useful results may be
obtained respecting the distribution of the




MODE OF ACTION.
EXPANSION.         Low pressure       Mean pressure      High pressure        Very high
engines,           engines,            engines,       pressure engines,
13 atmosphere    2~ atmospheres       5 atmospheres       10 atmospheres
boiler pressure.   boiler pressure.    boiler pressure.    boiler pressure.
Volumes.              kg.                kg.                kg.                 kg.
1.2.....14 5.........
1.33...........        13.33               12.10.........
1.50.........          12.20               11 05..
2.............                              9.16               8 31....
2.50...............   8.10              7 34
3................. 7.42                                        6.75
4................. 6.50                             5.90....
5.................... 5.40.
6                                                               5.05
8............                                                  4.60
o10.....................                               4.25                3.92
12............                            4.0.5               3.70
150.                                                           3.80                3.50
20.......'3.25




10                20
0 _A_ _osh.
1  1.5. 2           4           6 Vot'eine'  8          10E/l2pazsownlt                   1




66
steam and the resistances in passages,
pipes, etc.
The rate of the expansion normally employed ought to regulate the disposition of
the parts of the engine; an engine,constructed for a certain expansion will not
work so well with a much greater expansion. The reasons have already been given;
we add experimental confirmation as given
in a table from  " Engineering," in which is
shown the weight of sensible steam in the
cylinders of compound engines, each working with 3 deg. of expansion.
Number of engine.              1.
Expansions.................  5 6        10
Absolute pressures..........  5.4 k.     5 k,
Velocity of piston..       1.77 m.    1.49 m.
Weight of sens. steam in cyl
per hour and per h. p.......  6.38 k.  6.43 k.
Number of Engine.              2.
Expansions..6.55                      13.75
Absolute pressures......... 5.4 k.       5 k.
Velocity of Piston.........  2.175 m.    1.75 m.
Weight of sens. steam in cyl.
per hour and per h. p....    6.61 k.  6.43 k.




67
Numbea of Engine.             3.
Expansions.................  7.4   16.74
Absolute pressures..........  5.2 k.  4.7k.
Velocity of piston..........  1.98 m.    1.56 m.
Weight of sens. steam in cyl.
per hour and per h. p.......  6.84 k.    7.29 k.
This table shows that the increase of expansion in the same engine increases instead of decreasing the consumption of
steam. It is true that in the examples
cited, action with full expansion corresponds
to the least pressures and velocities of the
pistons, and that there should result a diminution of useful effect of steam and an increase of losses by interior condensation.
But the advantages due a greater expansion would more than compensate if it
should act under normal conditions, precisely what it does not do. With an engine
set to expand 5 or 6 volumes, expansions of
10, 12, or 15 volumes can be had only by a
corresponding reduced admission into the
first cylinder, so that one falls upon some of
the inconveniences of single engines, to say
nothing of the losses of pressure due to the




68
intermediate spaces and passages of double
cylinders.
We call attention to the ratio between
the weight of sensible steam and that of
the theoretic in order to warn the reader
of an error which has escaped the notice of
many persons. We annex a table....(See
page 69.)
The first thing remarked in this table is
that, while for most engines the sensible is
greater than the theoretic weight, in other
cases the ratio is one and less. Again,
where this ratio is small, the consumption
is increased, showing that the economy of
steam is only apparent, there being no reason for supposing that the generation in the
boiler is any less than in the other cases.
The conclusion is that we must not judge
of the economy of an engine by the low rate
of apparent expenditure of steam.
The explanation of this somewhat paradoxical result is simple, depending entirely
upon what has been said above of the action of certain single engines without jackets. The vaporization during the period of
expansion of the water condensed in the




Theoretic   Weight of    Ratio.   Consumptior,
Designation of engines. Absolute   Expan-   weight of   sensible                      of
boiler    sions.     steam      steam, P',     p'       fuel per
pressure.             per h. p.    per h. p.. I. p.
k.                  k.           k.                       k.
Woolf stationary engine.    5.15    10         4. 25        5.60        1 30         0.95.
Aigle, imperial yacht...    2.70     1.66      10           8.87        0.89. 
Abeille.............     2.12      1.54      11.30       10.50        0 90         2 25
Frigate, 250 h. p.......    2 47    1.54      11          11.10        1.00         1.75
Steamer, 600 h. p.......   2.10      2          9.50       10.79        1.14         1.78
Swift Steamer, 900 h. p.    1 98     1.66     10.70        12.00        1.12         1.64
Compound engines, 1....    5.40     5.60       5.20        6.38        1.22....
Id.           2...    5.40       6. 5       4.90        6.61        1.35
Id.           3...    5.20       7.40       4.70        6.84        1.57....
Hercules, tug.2.17                  1.66      10.35       13.00        1.25




70
cylinders, produces a total work greater
than that which corresponds,,to the apparent weight of water in the cylinder; although this work is often much, less than
that which is due to the amount of steam
-from the boiler. Besides, the steam in the
dead spaces expands during the period of
expansion.  The error is due to the fact
that the diagram indicates only the presence in the cylinder of the vapor in a gaseous condition during the period of admission; that is, a part only of the steam which
has entered the cylinder, which leaves it at
the end of the- stroke.  One cannot be too
careful in avoiding the errors which result
from a superficial examination. We insist
upon this point because it seems to have
escaped the notice of writers, the majority
of whom say nothing about it.
Though the value of the weight P' is not
of importance, it is otherwise with the quantity P, which represents the amount of water
vaporized in the boiler. Unfortunately the
direct measure of this quantity is attended with certain difficulties, and is possible
only in a few cases. Especially in marine




71
engines, where results are not to be obtained
by experiment, we are obliged to deduce the
weight of the fuel by assuming that we
know the weight of water vaporized per kilogramme of fuel (an element which can be
determined for a given fuel and generator),
or to calculate it approximately in terms of
p or P'.
In the first case, i e., when P is deduced
from the weight of fuel burned, it is necessary to take into account the water taken
up by the steam, which tends to increase
apparently the vaporization, and also to
take into account the loss of heat by extraction when the boilers are fed with water
containing salt. It is important to do this
when comparison is made of engines condensing by injection with engines provided
with surface condensers.
In land engines it is easier to measure
directly the water introduced into the boiler,
an element which should be determined as,
accurately as possible in experimeAts. In
the example cited, of a Woolf beam engine,.
the weight of water vaporized per H. P. was.




found to be 6.5 kilo.; hence we have the
following values:
P 6.50 k.    1.53     1.00
P' 5.60.1.30    0.85
p 4.25       1.00     0.653
At sea, where boilers of the same kind
and action may be assumed to have almost
identical vaporization, P may be estimated
from the amount of coal burned. For example, we may assume a vaporization of 8
kil. of water per kil. of fuel, which is not too
high an estimate for good coal, even with
salt-water feed. The value of - may then
p
be deduced, and a sufficient number of data
would determine the value of P in terms
of p.
An examination of results from a very
great number of engines, gives a mean ratio
of 1.55-nearly the same amount as that
obtained by direct measurement; so that
we may safely assume the value of - between 1. 5 and 1.6. In some cases, it is true,
this ratio is 1.3, and even 1.25; in others,
it is 2. We must conclude that in the first




73
case the vaporization is a little more than
our assumed figure (8 kil.), and that, in the
second case, there are special causes of the
loss of steam. We do not give 1.5 or 1.6
as an exact coefficient; but we think it
may be admitted as a mean value, and employed in projets.
A question occurs. The 50 or 60 per
cent. which should be added to the theoretic
weight of steam expended per hour to produce a IH. P. of 75 kilogrammetres upon
the piston, represents losses of all kinds,
from boiler to condenser. Can these losses
be reduced by suitable precaution and care
in the construction of engines? The answer is, that it is to these reductions, and
not to increase of expansion and tension,
that we are to look for future improvements.
It would be a great gain to reduce   to
1.40 or 1.33.
We find that there is little to gain in the
way of expansion; and possible increase of
tension is very limited, on account of the
difficulties in disposition of boilers, and those
attendant upon too high a temperature. It




74
does not seem possible, thedietically, to expend less than 3.50 kil. of steam; assume,
rigorously, 3.25 kil., answering to a tension
of 10 atm. and an expansion of 20 volumes.
We suppose the most conditions perfectly
favorable.
For the ratio-= 1.50, the weight of
p
water to be converted into steam per H. P.
is about 4.90 k. This, with a vaporization
of 8.5 k. per kilogramme of fuel (with surface condensation), would lead to a consumption of 0.58 k. per HI. P. per hour.
With the ratio  --  1.33, there would be
p
the same result, with a theoretic weight of
steam 3.70 kil., answering to an expansion
of 12 volumes only to a pressure of 10 atmospheres; an expansion much easier to
effect, and requiring dispositions much less
complex than expansions of 20 volumes.
Were it possible to combine the reduction
of the ratio with the minimum expansion,
the consumption would be reduced to
0.500 k.
So far, we have sought only for improve



75
ments in making use of the steam, without
regard to the method of its generation. It
is obvious that progress may be made in
this direction, and that it may be considerable. For example, if the production of
steam per kil. of fuel could be brought to
from 8.5 k. to 10 k.-a result not hopeless
-the expenditures would be reduced to
0.85; becoming 0.50 k., in the first case,
and 0.43 in the second.
Such results will certainly not be obtained
without great efforts; but we may reasonably hope to approximate them with means
already at our disposal, while, in our
opinion, it would be chimerical to attempt
directly to reduce consumption by means of
radical modifications in the generation and
use of steam.
An objection is often urged, that it is indeed possible to make economic engines,
but on condition of employing costly and
cumbrous devices, too heavy and bulky.
A steam-engine consists of a generator to
produce the motive vapor, and an engine to
put it to use. The weight of an engine is
in a certain measure controlled by its proper




76
disposition, especially with regard to rapidity of action, while the weight of the generator necessarily depends only on the
generation of steam and the pressure at
which the steam is produced. The weight
of the generator includes the weight of the
boiler and the water it contains.
Boilers may be referred to various elements; as to the unit of power, the unit of
grate surface, the unit of heating surface,
etc.
For our purpose the unit of weight of fuel
consumed is convenient; but care must be
taken not to draw from the figures conclusions which they do not warrant. It is obvious that the weight of the boiler, per
kilogramme of fuel, will be less in proportion'to the amount of fuel burned every hour,
and hence, that this weight will vary with
the activity of combustion, and will not in
any way give the measure of economical use
of fuel and metal; hence the considerable
differences in boilers of the same type. The
true methdd of determining the efficiency of
generators, with respect to weight, is to refer to, the kilogramme of steam —if only one




could get direct data of this element; but as
this must generally be deduced from the
weight of fuel, it is as well to make direct
reference to it.
We prefer, in all cases, to refer to the
weight of coal burned, rather than to the
square metre of grate surface. This would
be rigorously possible only in case the boilers burned the same quantity of coal; but
as the consumption may vary within wide
limits without a corresponding sensible
change in the production of steam answering to a kilogramme of fuel, we may ask,
what is the real value of such a mode of
estimation?
With the above reservations, our method
of measurement will permit us to take account of the possible results of a given kind
of boiler.
The following table contajins results corresponding to various kinds of boilers. (See
page 78 for table.)




Weight in kilogrammes of coal per hour.
DESIGNATION.                                                    KIND OF BOILER.
Of empty      Water.       Of full
boilers,                  boilers.
k.          k.            k.
North, Crampton.......    15.2           5.8          21        Locomotive.
North, 4 cylinders.......    24.6         7.4          32          Id.
North, moyennes Creusot    33.5           9.5          43          Id.
Francoise Ier............  28          20           48        Cylindric tubular. cast steel.
Machine compound......    58             17           75        Cylindric tubular.             0
Steamer, 900 h. p.......    49          26            75       Regulation.
Steamer, 800 h. p......    31           22            53         Id.
Ulster................    36           26.5          62.5     Tubular return flue.
Tasmanian...........        43          32            75         Id.
Sphynx..............         68          41           109       With galleries.
Eldorado.......              55          50           105          Id.
Roanoke................    76           42           118        Martin.
Brooklyn.......        65          51           116         Id.
Donawerth..35                       24            59       Lamb.and Summers.
Colombo................    75           55           120         Id.
Guayaquil..............    61     51           112        Spiral, Randolph and Elder.
Hirondelle.......      31           2            33       Belleville.




79
Because of the tendency toward high pressures, it is probable that there will be a return to that type of locomotive boilers, which
easily support pressures of 10 atmospheres,
and which being fed with fresh water will
give rise to no difficulty; always, with the
condition of their having sufficient draft.
It is clear that one of the first steps in improvement of marine boilers must be the
adoption of means for producing an energetic draft. These boilers weigh at most,
43 kil. per kil. of fuel consumed; in some
cases, 20 to 30 kil.; 40 kil. may be taken
as an average. Another solution may consist in the use of the Belleville boilers, which,
on the HIirondelle, gave 33 kil. But this
figure should probably be increased on account of the fact that the coal was not well
utilized. At any rate, we must admit the
existence of boilers which do not weigh,
water included, more than 40 kil. per kil.
of fuel consumed hourly. A boiler of this
kind feeding an engine expending only
0.5 k. per H. P., would weigh only 20 kil.,
water included, for the same unit.
Observing that the lighter boilers in com



80
bination with the most economic engines
weigh 60 kil. per H. P., and the total, 80
to 100 kil., and more, we see that an economy of weight of 40 kil. at least, and possibly from 60 to 80 per HI. P. is realized.
This weight, referred to an engine which,
for a velocity of 60 revolutions per minute,
weighs 80 to 100 kil. per H. P., represents
a bonus of 50 per cent., which would allow
an increase of the weight of the cylinders
and their accessories; for it must not be
forgotten that the excess of weight If due to
the increase of expansion affects only those
parts on which the steam acts, and not the
parts that transmit motion; while the parts
that relate to condensation follow the reduction of the weight of the boilers.  It is easy
to verify this assertion rigorously. The development of the power in every steam-engine corresponds to a certain volume described by the pistons in a unit of time.
This volume varies with the tension of the
steam, the degree of expansion, and the
efficiency of action of the engine.
The volume for a unit of power is found
by multiplying the volume of the cylinders




81
by twice the number of revolutions in a
unit of time, and dividing this product by
the indicated power. It can also be directly
obtained without knowledge of the dimensions of the engine, by dividing the value
of a unit of power by the mean effective
pressure on the pistons, as shown by the
indicator.
The volume, V, per H. P. is
-7rr2 2 c n.
P
P being the power; but as P    Tr rr' 2c n p,
p being the mean effective pressure of the
steam, we have V -
It is more convenient to refer this to the
minute. We have calculated for a great
number of engines of all kinds.
In certain engines, in which builders
have thought that they obtained lightness,
they have sacrificed the performance; the
volume per H. P. and per minute falling to
0.250 cm., and even to 0.200 cm. In most
engines of ordinary action with tension at
2.5 k. and 2.75 k., this volume is 0.300
m. c. to 350 m. c.
In the compound engines, mentioned by




Bramwell, acting with full expansion, but
at higher tensions, we find 0.385 cm. and
0.658 cm., as extreme values; the mean
being  0.450.  In engines with less expansion the values range from  0.300 to
0.400.
We infer that for the same number of
revolutions, the volume of the cylinders
will be increased only in the ratio of 1 to
1.5, an increase of volume corresponding to
an increase in weight from  1.25 to 1.30.
But suppose the weight rises to 1.50 or 2,
so as to take into account the presence of
jackets and the increase in section of slides
and ports. In stamping engines, nowadays
much used, the average weight of the cylinders with pistons and slides is 30 per
cent. of the whole engine; it follows that,
in this case, for a weight of 100 kil. per H.
P., we should have 130 kil., or an increase
of 30 kil.
We have seen that the minimum economy for boiler is 40 kil. We infer that a
reduction of boiler-weight due to better use
of steam, will permit the increase in weight
of cylinders and pistons required by increase of expansion.




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BECKWITH.  Observations on the Materials and
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BOYNTON. History of West Point, its Military Importance during the American Revolution, and the
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WOOD. West Point Scrap Book, being a collection of
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WEST POINT LIFE. A Poem read before the Dialectic Society of the United States Military Academy.
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HENRY. Military Record of Civilian Appointments in
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