272 
The Chair having been taken by Major Larcom,— 
Dr. Apjohn made a communication, the object of which 
was to demonstrate the fallacy of the doctrine that, in order 
to produce a given volume of vapour, having a given elastic 
force, the same quantity of fuel must be consumed, irrespective 
of the nature of the liquids employed. 
‘Tt has been frequently proposed to substitute the vapour 
of some volatile liquid, such as alcohol or ether, for that of 
water in the steam-engine, under the idea that by so doing 
fuel would be economized; and the proposal appears prima 
facie plausible, seeing that their boiling points are not only 
lower than that of water, but that the same is true of their 
specific heats, and of the latent heats of their vapours. This 
idea would seem to have struck at different times the minds 
of different persons, and the Rev. Mr. Cartwright, a gentle- 
man of great mechanical genius, and celebrated for his mecha- 
nical inventions, actually devised a most ingenious form of 
steam-engine,* in which the piston was to be moved by the 
vapour of alcohol. 
“Mr. Ainger, in a notice brought by him before the Royal 
Institution, London, in February, 1830, on the Economy of 
the Steam-Engine, would seem to be the first person who pub- 
licly dissented from such views ; and he has certainly the merit 
of having shown the insufficiency of the data generally used 
by those who, previous to his time, calculated that the substi- 
tution of more volatile liquids for water would lead to a con- 
siderable saving of fuel. - The conclusion, however, at which 
he arrives, that, leaving the original cost of the liquids out of 
consideration, water would be as economical a liquid as alco- 
hol or ether, I believe to be quite erroneous ; and as the ques- 
tion at issue is one of some practical importance, I shall proceed 
to state succinctly the method of calculation which I have em- 
ployed in discussing it, and the precise results at which I have 
arrived. 
* See Philosophical Magazine, vol. I. 
