272 



The Chair having been taken by Major Larcora, — 



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. 



" It 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. ■ Tbe 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. 



