Significance of the Chemical Constant. 23 



Therefore, unless by some curious coincidence is very nearly 

 1° for all the elements examined, one must conclude that 

 bi = 5/2R>. This, of course, is the usual value for the atomic 

 heat of a monatomic gas at constant pressure and precisely 

 what the classical, as opposed to the "degradation/' theory 

 would lead one to expect. 



The following table derived from figures kindly placed at my 

 disposal by Mr. A. C. G. Egerton indicates the value of the 

 experimental evidence. If 0^ = 5/211 the column headed 

 should be equal to 1°. If 0? is to become zero near the 

 absolute zero, one must assume that 6 has the values given 

 in column 3, i. e. that it happens to be very nearly 1° in all 

 these substances. 





0. 



C- 3/2 log A. 



6. 



Hg... 



.. l-820±0-082 



-1-633+0032 



0-976±0 030 



Cd ... 



.. 1-65 ±0-31 



-1-42 ±0-31 



119 ±0-40 



Zn ... 



.. 1-23 ±0-20 



-1-79 ±0-26 



1-11 ±0-30 



Ar ... 



.. 075 +0-06 



-1-65 ±006 



0-962+0-06 



H 2 ... 



..-1-23 ±015 



-1-68 ±0-15 



0935+0-14 



It is evident that the more accurate the determination the 

 more closely does 6 approach 1°. It is always 1° within the 

 limits of experimental error, and it seems most improbable 

 that this approach to the purely conventional unit of the 

 scale on which the temperature is measured should be a mere 

 coincidence. It is true that the equation ^t^RT is used in 

 deriving Clapeyron's equation and that a different formula 

 would be obtained if the degradation equation were used. 

 It seems unlikely though that this would compensate in such 

 a way as to invalidate the above argument. If not, one must 

 conclude that C j; = 5/2R, even at the lowest temperatures 

 and give up the degradation theories, which make it become 

 zero. 



This may be more acceptable if a further simplification is 



considered which puts the physical significance 

 chemical constant in a somewhat different light. 



of the 

 If the 



vapour pressure is written 



fh-fm^ 





f T 

 where /(T)=l c p dT, one must put 



Jo 



( 27r )3 2^3 2^5 2 

 Po— T3 - > 



