M. E. Wiedemann on the Specific Heats of Gases. 107 



to be the time for making an attempt to estimate the separate 

 parts of the heat of molecular motion — heat of atom, and of 

 atoms {atom- unci Atomenwarme) , according to Naumann — 

 which constitute the specific heat at constant volume, nor for 

 endeavouring to trace simple relationships between these — in- 

 asmuch as these relations would appear altogether different for 

 different temperatures, on account of the unequal alterations in 

 specific heats with alteration in temperature, which are not to 

 be entirely explained as small differences in heats of expansion. 



The alterations in the specific heats of gases with alterations 

 in temperature cannot be explained by taking into account the 

 deviations from the state of permanent gases. In the case of 

 ammonia, for instance, the alteration with the temperature is 

 much smaller than it is in the case of nitrous oxide and car- 

 bonic acid, although the latter are much more nearly perma- 

 nent gases than the former, as appears from the proportion of 



PV 



the values of -p ^ T • 



The smallness of the difference between the coefficients of 

 expansion of the gases show that the alterations in question 

 cannot be traced to this difference. 



Any attempt to explain the alterations in specific heat of 

 these gases from alterations in the specific heat of the elemen- 

 tary bodies composing them, say carbon and nitrogen, does not 

 appear feasible. For, in the first place, the experiments on 

 air show that the specific heat of nitrogen itself does not alter 

 with the temperature ; and further, the specific heat of all car- 

 bon compounds does not show alterations with the temperature. 

 One must rather accept F. Weber's view *, that the carbon 

 contained in these compounds is possessed of properties other 

 than those which characterize the carbon of carbonic acid. 

 It is not impossible that variations in the specific heat of carbon 

 may have something to do with the phenomena noticed in the 

 case of carbonic acid. 



The alteration in specific heats with the temperature may 

 perhaps be explained by supposing that, when one of the given 

 gases is warmed, a gradual dissociation is taking place which 

 eventually results in a loosening f of the combination of indivi- 

 dual atoms, and that this process is attended with the absorp- 

 tion of heat. The fact that the decomposition of nitrous oxide 

 is accompanied with evolution of heat is not opposed to this 

 explanation. Favre regards this evolution of heat as caused 

 by a change of the active oxygen of the oxide into inactive 



* Pogg. Ann. 1875, vol. cliv. p. 578 ; Phil. Mag. [IV.] vol. xliv. p. 800. 

 t Horstman, Ber. d. dent. Chem. Ges. ii. 723. 



