Determination of Chemical Constants. 15 



Nernst (I. c.) has calculated the constant in two other 

 cases : — 



Atomic n 4- t. Probable ~, .,■,-> 



weight. Constant. ^^ Constant (calc). 



A 39-88 0-75 ±0-06 0-893 



H 2 2-016 -1-23 ±0-15 -1-151 



The value of C obtained from all the experimental results 

 and from the probable errors, giving due weight to the 

 observations, is as follows : — 





-C (obs.) 





Weight. 



Mercury . 



1-633 





1-0 



Cadmium 



1-42 





o-io 



Zinc 



1-49 





0-12 



Argon 



1-65 





0-53 



Hydrogen . . 



1-68 



3-180 





0-21 





1-96 



(.'q mean 



1-96 



-1-622 





This value is slightly higher than the calculated (1*608), 

 but agrees within *85 per cent. 



Latent Heats of Vaporization. 



In the paper on the vapour pressure of mercury, cadmium, 

 and zinc already cited, values of X were given from the 

 relation : 



p = KT 



An 

 KT 



which was found to agree well w T ith the observed results. 



Here log p = log K — \ log T — ^3™ and it is assumed (Q p — c p ) 



remains constant and equal to unity. This will be approxi- 

 mately the case at ordinary temperatures where C p = 2*511 

 and Cp = 3H. It follows X T =\ — T, as an approximation. 

 The values of X have now also been obtained from the 

 rational vapour-pressure formula : 



l°gP = -RT+J HP J. /^ "Jo "KTjJo c ^ T + C < 

 which may also be expressed : 



P 



= KT ? V R£ 



where /(T) is a function depending on the change of atomic 

 heat of the solid. 



