10 ('apt. A. C. Egerton on the 



Between — 55 0, 6 and — 3°*4 C. Koref found the mean 

 c p = 6'68* ; while between 0° and 200° 0. the mean of 

 Barnes and Cooke's and Naccari's results give ^=6*58. 



From the values lor Xr given in Table II. the following 

 values of \ can be calculated : — 



Table III. 



T. Smith & Menzies. Knudsen. 



630 15452 15509 



473 15402 15520 



273 15341 15536 



234-2 , 15324 15535 



Above 250°, the value of c p is probably not constant; 

 the values obtained from Xtb will be neglected. 



The values obtained from the Smith and Menzies formula 

 vary more amongst each other than those of Knudsen, and 

 therefore this formula probably does not express the true 

 vapour pressure at the lower temperatures as well as the 

 latter. The mean of these values, viz. 15530 + 5, obtained 

 from the Knudsen formula will therefore be taken as most 

 closely approaching the value for the latent heat of vapori- 

 zation at absolute zero. 



At the melting-point : — 



4 m3/2 



4-571. 15 

 where 



4-571. 15 a,Tm+C 



X = 155.30 and -^ = -14*507, 



Itl 



T m = 234-2 and 2'51ogT m = 5'924, 



A -Ao = __ 8 . 133 and 1 rAyAo] = i-779 



a = 21. 10- 5 and A . _L_ . aT,f = 0-0439. 

 lo 4-D71 



p = 0-000001970 mm. and \ogp= -5*7055 mm. 



= — 8'586 atmos. 



* This value is slightly low in comparison with that of other 

 observers (see graph), and the average variation (Winkelmann) 

 0-0000069 per ° C. would lead to a value about 673, i. e. X T =273= 15538. 



