12 Capt. A. 0. Egerton on the 



2*723 — 1*608 = 1*115. In a previous communication (Phil. 

 Mag. xxxiii. p. 193, 1917) results were given of determinations 

 at low pressures of the vapour pressures of solid cadmium 

 and zinc. Although these results were not carried out with 

 the precision necessary to obtain an accurate value for the 

 chemical constants, it seems worth while to inquire whether 

 the constants, deduced above, lie within the limiting values 

 of the constants obtained from the observed results, taking 

 into consideration the experimental errors. 



Chemical Constant of Cadmium. 



From the mean of the most reliable observations, the 

 following two points are chosen, which lie on the smoothed 

 curve of the vapour pressure : 



T 1 =471-8±l°abs., log p= -3'54(6)±0*02. 



T, = 532-5 ±1° abs., logp= -2*11(8) ±0*02, 



From Lindemann's melting-point formula : 



, = 3-1,10^^/^3, 



where T = 594° abs., 



A = U2*4, 

 v= 13*0 : 

 v = 3*03 . 10 12 



ind /3v = 147*5 



£*_ 147-5 _ A . 01oi!0 . r A i- A ( 



]v_ 147*5 _ .q 1962 . r A L^ol__ 9.599 

 L\ "471-8 "" Ud ' L I\ J J0J " 



•** |=5-K=^ 70 ^[V°]=- 10 ' 2;!9 - 



9a 2 i>T 

 Writing aT 3/2 = - , the value of a can be estimated 



for (say) 291° C. 



«: = 2*25 . 10" G (mean of Gruneisen's and Richard's 



results), 

 x = 2S'8 . 10- 6 (Matthiessen 1866) at 20° C, 

 u=13-0. 



_9x(28-8) 2 x 13*0 x 291. 10- 12 _ „ in : 5 

 ■"• a__ 4-18x2-3 .lF^Sl) 5 -> J6 ' W ' 



This lies close to the value found for zinc. 



