42 Mr. Meikle on Specific and Latent Heat, fyc. 



weight of water. But the quantities of heat thus expended in 

 filling the two equal cylinders, will be as the above numbers 

 multiplied by the respective densities of the vapours. Now 

 the specific gravity of such alcoholic vapour, according to the 

 Doctor, is 2*3 times that of steam. Hence the expense of 

 heat in the two engines will be as 1055*6° to 1115*7°, or 60° in 

 favour of steam. 



A compensation is wanting in both cases for the heat spent 

 in warming the glass of the condensing globe, and of the ex- 

 terior vessel in the apparatus. The steam warmed it 6°*5, and 

 the other 3°. But these compensations, if of uncertain mag- 

 nitude, are proportional to the ranges through which the glass 

 was heated, multiplied by the densities of the respective va- 

 pours ; that is, in the case before us, as 6'5 to 3 x 2*3 = 6*9, 

 which are numbers so nearly equal that the omission of cor- 

 rections in that ratio cannot materially affect the comparative 

 result; at least it gives steam no advantage over the other. 



I know of no direct experiments from which I could make 

 a comparison between the expenditures of heat in engines of 

 higher pressure. But from Dr. Ure's experiments it appears, 

 that when the forces of these two vapours are increased and 

 equal, the ratio of the density of alcoholic vapour to that of 

 steam will rather be increased ; and assuming that their latent 

 heats, though variable, maintain their former ratio*, and that 

 the same thing holds of the specific heats of their liquids, it 

 were easy to show that for higher pressures, the comparison 

 would be still more favourable for steam. Similar results 

 would follow, calculating on M. Clement's hypothesis of latent 

 heat. 



It thus appears, that the vast powers of alcoholic vapour are 

 not so easily produced as some are apt to imagine. Nor is 

 this the only imperfection in the scheme ; for it is worthy of 

 remark, that one gallon of water will go almost as far as three 

 of alcohol. Add to all this, that the very grossness and con- 

 sequent inertia of alcoholic vapour at high temperatures, would 

 operate as a dead weight on a nice machine ; because consi- 

 derable force would be requisite to move it with sufficient ra- 

 pidity through the pipes, valves, &c. The power unavoidably 

 lost in this way, even in a steam-engine, is perhaps greater 

 than many are aware of. 



H. Meikle. 



* For corrections in Dr. Ure's latent heats, see the second edition of 

 his valuable Chemical Dictionary; and Philosophical Magazine, October 

 1822, and October 1825. 



VI. On 



