208 Dr. A. Naumann on the Specific Heat of Gases 



tion of one atom ia=-), we must start from the experimen- 

 tally determined specific heats of the most perfect gases — that is, 

 of oxygen, nitrogen, and hydrogen. 



As a consequence of equation (4), which determines the heat 

 of atomic motion, we have for the heat of motion of one atom 



fl ^ 7 , -5(7'-7) = y' -0-17275 



where its numerical value ( = 0*0691) has been substituted for 

 </— 7; while for 7' Regnault' s experimental values, as given in 

 Tables which follow lower down, and for n the number of atoms 

 contained in a molecule must be taken. In this way closely 

 accordant empirical values of a, the heat of motion of one atom, 

 are obtained for those gases with diatomic molecules which 

 nearly follow the laws of Mariotte and Gay-Lussac — namely, 



For Oxygen, O 2 . . 

 „ Nitrogen, N 2 . 

 „ Hydrogen, H 2 

 „ Nitric oxide, NO . 

 „ Carbonic oxide, €0 



0-0339 

 0-0320 

 0-0316 

 0-0339 

 0-0321 



„ Hydrochloric acid, HC1 . 0-0303. 



Moreover for a few other gases with triatomic, tetratomic, pen- 

 tatomic, and hexatomic molecules, the formation of which from 

 their constituents, supposed in the gaseous state, takes place with 

 condensation, we have — 



For Hydrosulphuric acid, H 2 S . 0-0377 



„ Ammonia, N H 3 * . . . 0-0318 



„ Marsh-gas, H 4 t . . . 0-0310 



„ Ethylene, 2 H 4 f . . . 0*0363 



If we take into consideration the close agreement of these 

 numbers relatively to the possible degree of accuracy J of the 

 experiments, and remember that, as was shown above, the heat 

 of expansion is to the heat of molecular motion in a simple ratio, 

 the idea readily occurs, in relation to the value of the numbers 



* Regnault is of opinion that his value for the specific heat of ammonia 

 is " no doubt a little too low " (Mem. de VAcademie des Sciences, vol. xxvi. 

 p. 162). 



t Regnault could not get marsh-gas or ethylene perfectly pure. Ibid, 

 pp. 139 & 141. 



% On this point see the special description of Regnault's separate ex- 

 periments, op. cit. passim. 



