( 100 ) 



So for tlie relation is tound : 



be 



Vrhc' Vc 



-i— = ^ r (330 



be Vc — be 



Now at the critical point about 



vc=2,20be ; —vebc" = 0,S8 ; be' =='/,, = 0,i)7 



so that we get: 



0,38 2,20 



n 



0,07 1,20 

 hence 



0,32 = 1,83 71, 



so that for ?i a value is found which is only slightly below 3. If 



we take the value 0,39 for — Vcbc" (van der Waals gives even the 



ƒ— 4 2,8 



value = — =: 0,41 on j). 1227 loc. cit.), we find accurately 



ƒ 6,8 



?z = 3, Hence it seems that in the neighbourhood of the critical point 



the slight number of complex molecules which still remain, are on 



an average associations of triple molecules. 



Hence we may wiite for Tc by approximation : 



I shall have to conclude now ; the fuller discussion of this interest- 

 ing problem, only just alluded to in §§ 35 and 36, I must postpone 

 to a further occasion. 



Clarens, April 22"^ 19J1. 



Cliemistry. — "Action of sunlight on allocinnamic acid." ]iy 

 Dr. A. W. K. DE Jong at Buitenzorg. 



Some time ago (Ber. 35, 2908 [1902]) Ruber found that ordinary 

 cinnamic acid, in the solid condition, is converted by the action of 

 sunlight into «-truxillic acid. A number of other compounds possessing 

 a 4-riug have been obtained in a similar manner. 



Among the acids obtained by the splitting of the coca alkaloids 

 occurs, besides «-truxillic acid, also a structure-isomer, jS-truxillic acid. 

 It seemed to me very probable that this compound might form from 

 a/Zöcinnamic acid, which always occurs among the split off acids. 



The a//öcinnamic acid, used in this investigation, was prepared 

 from the split off acids ; it melted at 41° — 42°, the melting point of 

 Erlenmeyer's wocinnamic acid. It was readily soluble in both petro- 



