1813.] Specific Heat of the different Gases. 137 



of a small reservoir, containing a thermometer, a current of two 

 different gases, the one hot, the other cold. Knowing the tem- 

 perature of the two gases before their mixture, and that of the 

 mixture, it was easy to infer the ratio between their respective 

 specific heats. This process, besides that it does not give us the 

 ratio between the specific heat of the gases and that of water, is 

 attended with another inconvenience. When only small quan- 

 tities of gas are employed, a great part of their heat is communi- 

 cated to the vessels in which the mixture is made, which may 

 lead to erroneous conclusions. Accordingly, as he made his 

 experiments at first on the gases that can be most conveniently 

 procured, such as air, hydrogen, carbonic acid, &c. which, as 

 will be seen afterwards, do not differ much in their capacity for 

 heat, he was induced to believe that the same volumes of all the 

 gases had the same capacity. However, he afterwards published 

 a note, * from which we see that he had brought his process to 

 perfection by operating upon large quantities of gas. By that 

 method he ascertained that hydrogen and carbonic acid have 

 different specific heats, and the numbers which he assigns ap- 

 proach to those which we have ourselves obtained. This induces, 

 us to remark to the commissioners that a first memoir having for 

 its motto Tectus magis cestuat ignis, which contains our most 

 important results, was deposited in the hands of the Secretary of 

 the Institute on the 3d of February, 1812, more than five 

 months before that note of Gay-Lussac was published in the 

 Annales de Chimie. 



Among the attempts made to determine the specific heat of 

 the gases, we ought to reckon the table drawn up by Mr. Dalton 

 from principles purely theoretical, founded on this hypothesis, 

 that the quantities of heat belonging to the ultimate particles of 

 all elastic fluids ought to be the same under the same pressure 

 and at the same temperature. His table is as follows : — 



Hydrogen gas 9*382 Nitrous gas 0*777 



Azotic gas 1-866 Oxide of carbon 0777 



Atmospliciic air 1*759 Vapour of alcohol 0*586 



Ammonia 1'555 Sulphureted hydrogen . .0*5S3 



Olefiant gas 1*555 Nitrous oxide gas 0*519 



Oxygen 1*333 Vapour of nitric acid . . .0*491 



Carbureted hydrogen .... 1 *333 Carbonic acid 0*191 



Aqueous vapour 1*166 Muriatic acid 0*424 



Vapour of ether 0*818 



Such arc the results of the investigation of this subject hitherto 

 made. 13y comparing them together, it is easy to see how far 



* Ann. dc Chim. lxxxiii. 106. 



