Mr. Haycraft on the Specific-Heat of the Gases. 20l 



The importance of the subject so impressed my mind, that I 

 determined to spare no pains in the prosecution of the inquiry, 

 and therefore I willingly withheld my first experiments from 

 the public eye, until, by a fresh series, I might present them 

 with the greater confidence. The apparatus employed in these 

 experiments was calculated to operate upon greater quantities 

 of the gases than the former one, and as every precaution 

 which had been suggested was adopted, they have, perhaps, 

 given even more decisive results than the last. The results 

 themselves, however, are in every important particular exactly 

 the same. It is also but justice to myself to state, that the 

 conclusions which the former experiments led to, were exactly 

 the reverse of what I had anticipated, and that they seemed 

 at the time totally opposed to the doctrines of Black and 

 Crawford, which I am still disposed to credit to a limited de- 

 gree. 



Before I enter into the detail, it will be necessary to take 

 notice of the modes in which former experimenters have pro- 

 ceeded in these inquiries, and to point out what I conceive to 

 have been the sources of fallacy in some of their conclusions. 

 Of all these modes, none were more elegant than that adopted 

 by Professor Leslie ; but as he himself states that their re- 

 sults were discordant with each other, it seems unnecessary 

 to enter into a description of it. Dr. Crawford's method con- 

 sisted of inclosing two different gases (previously exposed to 

 muriate of lime, for the purpose of depriving them of their 

 watery vapour,) in two close vessels of equal size and weight; 

 these being heated to exactly the same temperature, by a very 

 ingenious contrivance, were at the same time plunged into two 

 vessels, containing water of a lower temperature : these vessels 

 were also of the same size, form, and weight : then, by means 

 of accurately adjusted thermometers, he ascertained the com- 

 parative rise of temperature occasioned by the two gases, and 

 hence he determined their specific heats. 



1 know of no imperfection in this mode, excepting that the 

 quantities of the gases were so small, that the results could 

 not be obtained with sufficient accuracy. 



This defect is entirely obviated by the method adopted by 

 Messrs. De la Roche and Berard : their apparatus consisted 

 of a column of water, so adjusted as to act with a constant and 

 equal pressure in a close vessel containing air ; which being 

 gradually expelled by the superincumbent water, pressed on 

 the outward surface of a bladder containing the gas whose ca- 

 pacity was to be examined. From this bladder the gas was 

 propelled through the calorimeter: this consisted of a vessel 

 containing water of a low temperature, through which a spiral 



Vol. 64. No. 317. Sept. 182-t. C c tube 



