and on Alcoholic Engines. 35 



Mr. Haycraft's experiments are detailed in the Transactions 

 of the Royal Society of Edinburgh, vol. x., and in the Philoso- 

 phical Magazine, vol. lxiv. His apparatus consisted princi- 

 pally of two equal cylinders or forcing pumps, one of which 

 made a certain volume of heated air circulate through a pipe 

 immersed in cold water ; and the other did the same thing 

 with an equal volume of some other gas. Their specific heats 

 under equal volumes, were then compared, supposing them 

 proportional to the effects they had in separately heating equal 

 quantities of the cold water. 



For the purpose of abstracting moisture from the gases, 

 each cylinder contained some muriate of lime : but it would 

 have been fully as satisfactory had the gases been rendered 

 dry previously to their introduction, for this salt might again 

 give out moisture as the temperature rose. Besides, if the 

 absorbent substance abstracted more moisture from one gas 

 than from the other, it would at the same time reduce its 

 elasticity the more, and with it the capacity for heat under a 

 given volume, which was that of the contents of the apparatus. 

 We are not informed whether the interior parts of the appa- 

 ratus were oiled or not; for if any substance capable of eva- 

 poration or of combining with the gases came into contact 

 with them, there is reason to suspect the consequences. That 

 the gases were somehow contaminated during the operation, 

 appears from their being less pure at the end of the process 

 than at the commencement, even when they ought to have 

 been more free from moisture, after having been all the while 

 exposed to muriate of lime. 



From perusing the account of Mr. Haycraft's experiments 

 on mixtures of gases and vapours, I am not so clear about ac- 

 quiescing in the conclusions he has drawn, regarding their 

 specific heats ; as from several circumstances it is doubtful if 

 they be sufficient to overturn the hypothesis of equal specific 

 heats belonging to equal volumes whenever the elasticities and 

 temperatures are equal. As to his experiments on carburetted 

 hydrogen, I rather suspect some decomposition had taken 

 place, by friction, change of temperature, &c. ; and if such 

 were the case, there is reason to think that both the elasticity 

 and heat might undergo some change. It would have ren- 

 dered such experiments more satisfactory, had the apparatus 

 been provided with gauges by which the elasticities of the in- 

 cluded gases could have been ascertained or compared at any 

 stage of the process ; for if these elasticities differed more than 

 in the ratio of the temperatures of the calorimeters increased 

 by 44-8°, there could be little doubt that all was not correct. 

 The apparatus, it is true, might have been constructed to 



E 2 maintain 



