6 28 
ENGINES. 
Table of the pressures, temperatures, and 
expansibility of steam, equal to the force 
of the atmosphere. 
rt o ^ £ f* 
cj w 
ume t 
inp; fo 
will 
contii 
re of 
2. 
o 1$ p % 
• -1 
> £ ~~ S 
■2 kg “ ^ 
£ 
s 
§ js ag ■£ a 
E ~ p £ ~ «3 
rt 
CL 
X 
“ £■§, 
w 
° E 'O'rt o 
No. 
stea 
and 
pan 
equ 
atm 
U +4 V CJ 
<U O 
u *-*<*> 
3 be o b 
IS .5 £ r 
& |£-S 
rJKa 
C 
O <i> 
feo‘2 
Q 5^ 
^ 'MfcJM|T+yr|-+H|^w|ewIf<H|c»W|c> 
° C ^ 'O O CD N « ^ 
‘rti(MC <, 5C' , 500C^C < D , OiryCOU-i'-CO 
<M<N<NCNCN<M<N<M5M<MCMOI 
i «» "2 oJ 
oj C s 
cx ^ 
*s nj 
c <U > 
5 o *-• i 
” -5 ^ t' 
® r s->s 
i« «; o g 
o > p 
.. o £ * 
<u 
c3 
<2-5-^ a. 
■*-» 4-» p 
c o to 
II 2fos 
W-g g 3 
In this manner, by small additions of tem- 
perature, an expansive power may be given 
to steam, which will enable it to expand 50, 
100, 200, 300, p &c. times its volume, and 
still have the same force as the atmosphere. 
Upon this principle Mr. Woolf has taken 
out a patent for various improvements on 
the steam-engine, a short account of which 
we shall subjoin in the words of the specifi- 
cation. 
“ If the engine be constructed originally 
with the intention of adopting the preceding 
improvement, it ought to have two steam- 
vessels of different dimensions, according to 
the expansive force to be cbmmunicated to 
the beam, for the smaller steam-cylinder 
must be a measure for the larger. For ex- 
ample, if steam of 40 pounds the square inch is 
fixed on, then the smaller steam-vessel should 
be at least one-fortieth part the contents of 
the larger one. Each steam-vessel should 
be furnished with a piston, and the smaller 
cylinder should have a communication both 
at its top and bottom, with the boiler which 
supplies the steam, which communications, 
by means of cocks or valves, are to be alter- 
nately opened and shut during the working 
of the engine. The top of the small cy- 
linder should have a communication with the 
bottom of the larger cylinder, and the bot- 
tom of the smaller one with the top of the 
larger, with proper means to open and shut 
these alternately by cocks, valves, or any 
other contrivance. * And both the top and 
bottom of the larger cylinder should, while 
the engine is at work, communicate alter- 
nately with a condensing vessel, into which a 
jet of water is admitted to hasten the con- 
densation. Tilings being thus arranged, 
when the engine is at work, steam of a high 
temperature is admitted from the boiler to 
act by its elastic force on one side of the 
smaller piston, while the steam which had 
last moved it has a communication with the 
larger cylinder, where it follows the larger 
piston now moving towards that end of its 
cylinder which is open to the condensing 
vessel. Let both pistons end their stroke at 
one time, and let us now suppose them both 
at the top of their respective cylinders ready 
to descend; then the steam of 40 pounds 
the square inch, entering above the smaller 
piston, will carry it downwards, while the 
steam below it, instead of being allowed to 
escape into the atmosphere, or applied to 
any other purpose, will pass into the larger 
cylinder above its piston, which will take its 
downward stroke at the same time that the 
piston ot the smaller cylinder is doing the 
same thing ; and, while this goes on, the 
steam which last filled the larger cylinder, 
in the upward stroke of the engine, will be 
passing into the condenser, to be condensed 
in the downward stroke. When the pistons 
in the smaller and larger cylinder have thus 
been made to descend to the bottom of their 
cylinders, then the steam from the boiler is 
to be shut off from the top, and admitted to 
the bottom of the smaller cylinder, and the 
communication between the bottom of the 
smaller, and the top of the larger cylinder, is 
also to be cut off, and the communication to 
be opened between the top of the smaller 
and the bottom of the larger cylinder ; the 
steam which, in the downward stroke of the 
engine, filled the larger cylinder, being now 
opened to the condenser, and the communi- 
cation between the bottom of the larger cy- 
liiule r and the condenser cut off; and so on 
alternately, admitting the steam to the dif- 
ferent sides of the smaller piston, while the 
steam iast admitted into the smaller cylinder 
passes alternately to the different sides of the 
larger piston in the larger cylinder, the top 
and bottom of which are made to communi- 
cate alternately with the condenser. 
“ In an engine where these improvements 
are adopted, that waste of steam which arises 
in other engines from steam passing the 
piston, is totally prevented, for the steam 
which passes the piston in the smaller cylin- 
der is received into the larger.” 
Mr. Woolf has also shewn how the preced- 
ing arrangement may be altered, and has 
pointed out various other modifications of 
his invention, and the method of applying 
his improvements to steam-engines which 
are already^ constructed. 
On the pozver of steam-engines, and the 
method of computing it . — From the account 
which has been given of the steam-engine, 
and the mode of its operation, it must be 
evident that its power depends upon the 
breadth and height of the cylinder, or, in 
other words, on the area of the piston and the 
length of its stroke. If we suppose that no 
force is lost in overcoming the inertia of the 
great beam, and that the lever by which the 
power acts is equal to the lever of resistance ; 
then, if steam of a certain elastic force is ad- 
mitted above the piston, so as to press it 
downwards with a force of a little more than 
100 pounds, it will be able to raise a weight 
of 100 pounds hanging at the end of the 
great beam.. When the piston has descend- 
ed to the bottom of the cylinder, through 
the space of four feet, the weight will have 
risen through the same space ; and 100 
pounds raised through the height of four 
feet, during one descent of the piston, will 
express the mechanical power of the engine. 
But if the area of the piston, and the length 
of the cylinder, are doubled, while the ex- 
pansive force of the steam, and the time of 
the piston’s descent, remain the same, the 
mechanical energy of the engine will be qua- 
druple, and will be represented by 200 
pounds raised through the space of eight 
feet during the time of the piston’s descent. 
The power of steam-engines therefore is, 
ca'teris paribus, in the compound ratio of the 
area of the piston, and the length of the 
stroke, fi hese observations being premised, 
it will be easy to compute the power of 
steam-engines of any size. 
Thus, let it be required to determine the 
power of steam-engines, whose cylinde- is 
twenty-four inches diameter, and which 
make twenty-two double strokes in a mi- 
nute, each stroke being five feet long, and 
the force of the steam being equal to a pres- 
sure of twelve pounds avoirdupois upon 
every square inch. The diameter of the 
piston being multiplied by its circumference, 
and divided by four, will give its area in 
. , ,24 >; 3.1416 X 24 
square inches ; thus : — 452.4 
4 
the number of square inches exposed to 
the pressure of the steam. Now if we multi- 
ply this area by twelve pounds, the pressure 
upon every square inch, we shall have 452.4 
X 12=5428.8 pounds, the whole pressure 
upon the piston, or the weight which the 
engine is capable of raising But since the 
engine performs 22 double strokes, five feet 
long, in a minute, the piston must move 
through 22x5x2=220 feet in the same 
time ; and therefore the power of the en- 
gine will be represented by 5428.8 pounds 
avoirdupois, raised through 220 feet in a mi- 
nute ; or by 10.4 hogsheads of water, ale 
measure, raised through the same height in 
the same time. Now this is equivalent to 
5428.8x220=1 194336 pounds, or 10.4x220 
=2288 hogsheads, raised through the height 
of one foot in a minute. This is the most 
unequivocal expression of the mechanical 
power of any machine whatever, that can 
possibly be obtained. But as steam-engines 
were substituted in the room of horses, it has 
been customary to calculate their mechanical 
energy in horse-powers, or to find the num- 
ber of horses which could perform the same 
work. r l his indeed is a very vague expres- 
sion of power, on account of the different de- 
grees ot strength which different horses pos- 
sess. But still, when we are told that a 
steam-engine is equal to 16 horses, we have 
a more distinct conception of its power, than 
when we are informed that it is capable of 
raising a number of pounds through a cer- 
tain space in a certain time. 
Messrs. Watt and Boulton suppose a horse 
capable of raising 32,000 pounds avoirdu- 
pois, one foot high in a minute, while Dr. 
Desaguliers makes it 27,500 pounds, and 
Mr. Smeaton only 22,916. If we divide-, 
therefore, the number of pounds which. any 
steam-engine can raise one foot high in a 
minute, by these three numbers,, each. quo- 
tient will represent the number of horses to 
which the engine is equivalent. Thus in the 
