'Theory of Surface Forces. 313 



In the immediate neighbourhood of the critical temperature 



\/l — 3 may be neglected with respect to ft and we get the 

 formula of van der Waals : 



which is only true in the neighbourhood of the critical 

 temperature, while my formula is general. 

 For ether I have found : 



H=145(l-S) = -119(l-$) 2 . 



For r = 20°. 150°. 190°. 



Formula H = 16-49 3*12 0'15 



Observed H= 16*49 2'98 0"16 



Ohservation. — Mathias has found for pi—p 2 - 



p l + p. 2 —2p I , — a(l—$), 



where a denotes a constant. 

 We have thus : 



R = K (p-p,)(p 1 + p i -2 P/ ) (10) 



In the neighbourhood of the melting-point the density of 

 flic vapour may be neglected with respect to the density of 

 the liquid, and lor many substances the density p at the 

 melting-point is about three times the critical density. 

 For instance, Mathias has calculated * : — 



c , , . n One-tlurd of the 



substance. Pi.. -, ., , , c 



K density at t°. 



C G H G I 03038 0-3000 0° 



C (1 1LF1 0-3543 03491 -0°75 



C 6 H 5 C1 03665 0-3635 35° 



C c H,Br 0-4860 04836 53° 



CJT-I 0-5843 0-5808 77°-S 



Cn 3 OII 0-2775 0274 0° 



C 2 H,OH 0-2786 0-269 0° 



C,H 7 OII 0-2777 0-2733 0° 



(C 2 H,),0 0-2631 2453 0° 



CH a COOII 0-3516 0-3510 lG°-3 



CC1, 0-5557 05440 0° 



SnCl 4 0-7414 07465 14°9 



S0 2 0*5200 0-5043 -30° 



* E. Mathias, Lc Point Critique cles Corps Furs, p. 10. 



