of Zinc , Cadmium, and Mercury. 43 



3. Results. 



The results which have been obtained could no doubt be 

 represented in a similar manner to that of mercury (liquid) 

 with a formula of the Rankin type, or the Biot type. 



For mercury Knudsen found 



logjp=!0-5724-0-8471ogT- — ,£— . 



But since the vapours of these metals have proved to be 

 monatomic, it is worth while to find out how closely the results 

 agree with the formula derived from the Clausius equation : 



X=RT 2 



dlnjj 



dT 



and A=X — (C — Op)T, where (J is the molecular heat of 

 solid, and Qp is the molecular heat of the vapour at constant 

 pressure; whence 



fop = '— -JL — / ~ P \ log T + constant ; 

 but assuming * ^ _. __ 5 ^ B 



hence , _ A° 



p = K. r r~*e KT . 



It is found that for cadmium 



2-77 . 10 4 



p = 5-21 . 10 13 T _l e ET dynes per sq. cm., 



logp = 10*5979-(h51ogT ^- (mm.). 



For zinc, 



3-28 . 104 



i — 



p = l'17 . 10 14 T Je ET dynes per sq. cm., 

 log jo -10-9443 -0-5 log T--^ mm. 



Hence for cadmium \ = 2*77, whereas on calculation 

 according to the formula of Nernst, 



X = TB. S'D log T B , 



the latent heat of vaporization 



Xo=2-70. 



* The value of X calculated in this way r-annot be taken as quite 

 correct, as the assumption with regard to specific heats is not true. When 

 due allowance for the changes of specific heat has been made, the values 

 of k, X , and the index of T will probably be slightly different ; but by 

 assuming the index of T to be— h, the simplest approximation is obtained, 

 wherewith to compare the results obtained for the different elements. 



