and PoxQer of BrowrCs Gas Machine. 369 
heated air and vapour in the cylinder, when the condensation 
takes place, then. 
450 + 2^ 
500 
the volume of the air when heat- 
ed, its volume at 50° being unity ^ ; and the force of air being 
inversely as the space it occupies, taking the pressure of the at- 
mosphere at 30 inches, we have, 
1 •-T^rr^ : : 30 : 30 ^ resistance of the con- 
tents of the cylinder when cooled to 50° : consequently 
30 =:the power in inches of mercury without 
reduction for friction. 
Put the grains of combustible matter that will heat one 
cubic foot of water one degree ; and as 0.00035 is the specific 
heat of air when that of an equal volume of water is unity -J-, 
0.00035 g t will heat one cubic foot of air t degrees ; and if w 
be the weight of a cubic foot of the gas or combustible in grains, 
, 0.00035 1 r. 1 -11 1 1 • 
we nave — ttie volume of gas that will heat the air 
W o 
in the cylinder when its capacity is denoted by unity. 
There will be a loss of heat in warming the cylinder, and the 
solid matter against which the flame and heated air must act at 
every stroke ; these causes of loss I will not attempt to estimate, 
but proceed to compare the gas machine with the steam-engine. 
The volume of steam produced by a bushel of coals (84 lb.) 
is 14,700 cubic feet, which, when condensed, gives a pressure 
equivalent to 26 inches of mercury on the piston. We have 
found the pressure on the piston in the gas cylinder to be 
30 inches of mercury, under similar circum- 
stances ; therefore, that the powers may be equal, and x be the 
volume of air to be heated to produce the same effect, we must 
have 1 4700 x^6 = S0x ^ ; 
\ 450 -j- ^ / ’ 
14700 X 26 
or. 
30 
A 
V 4:50 + tj 
= X. 
* Principles of Warming and Ventilating^ 2d edit. p. 285. 
-{- Idem^ p. 281. 
