14 Oapt. A. C. Egerton on the 



Chemical Constant of Zinc. 

 The chemical constant of zinc can be obtained from the 

 vapour-pressure measurements in a similar manner. 

 Taking the points : 



at 553° abs., logp= -3'35±0'02, 



at f,25°abs., log p= -1'92±0'02. 



The temperature measurements were considered to have a 

 probable error ±1°(1. 



Ttie value of (3v obtained from the melting-point formula 

 is 234, and that from specific-heat measurements (Koref, 

 Ann. d. Phys. xxxvi. 1911, and Pollitzer, Z.S. f. Elek. xvii. 

 p. 5, 1911) 'is 235. 



At ^234 =(> 42312; rA^l = _ s . 025j 

 li 5oo |_ h J 



and ^ = 234 =0 . 37440: pA-A 

 lo 62o 



[A-Aoj 

 L Tx J 



Pollitzer gives a from the specific-heat measurements 

 as 5-4. 10~ 5 . 



From the coefficient of expansion — 26 x 10 ~ 6 cm. 

 (National Phys. Laboratory) ; compressibility 1*69 . 10 -i2 

 per dyne/cm. 2 , and atomic volume 9*22 c.c, at temperature 

 291° abs,, a becomes 4'65 . 10~ 5 . 



The value 5*4 . 10 ~ 5 will be used. 



Inserting these values for a, -^ °, and p in the 



vapour-pressure formula, two equations are obtained, from 

 which C=1'23. 



As before by differentiation, a change of temperature 

 2° 0. will alter' the constant +0'26, so that the theoretical 

 value l'llo lies within the limits of experimental error. 



Values of Chemical Constants, 



Both for cadmium and zinc therefore, the result lies 

 within the experimental error and there appears to be 

 no doubt that the chemical constant may be represented 

 by a formula G -fl'5 log M as shown in the table. 



— Chemical Constants. 



n >. <- Probable ~ . , x 



Constant, error Constant (calc). 



1-820 ±0032 1-845 



1-65 ±0-31 1-468 



1-23 +0-26 1-115 





Table IV 





Atomic 



Mercury 



weight, 

 . 200-6 



Cadmium .. 



. 112-4 



Zinc 



G5'07 



