( 101 ) 



leum ether and ordinary ether. The substance was dissolved in a 

 little ether and the solution poured into a glass basin when the acid 

 was obtained in beautiful crystals. 



After exposure to fall sunlight for seventeen mornings an exami- 

 nation was made to see what change had taken place. 



It was very plain that the substance was no longer the same, as 

 it consisted of a quite opaque mass whereas the original ci-yslals 

 were beautifully transparent. 



It exhibited no definite melting point; at 95° it became somewhat 

 soft to finally melt completely at 165°. Only a portion dissolved in 

 ether. The undissolved mass melted just above 200° (/i-truxillic acid 

 melts at 206°). In ammoniacal solution it gave a heavy precipitate 

 with barium chloride and the acid isolated therefrom melted at 206°; 

 wdien mixed with ^-truxillic acid, isolated from the coca-acids, the 

 melting point remained unchanged. 



From the ethereal solution a further quantity of ,i-truxillic acid 

 was obtained and also «-trnxillic acid, ordinary cinnamic acid and a 

 trace of oil. 



In all, 0.64 gram of /i-truxillic acid, 0,1 gram of «-truxillic acid 

 and 0.2 gram of cinnamic acid were obtained. The «-truxillic acid 

 has been formed in all probability, from the ordinary cinnamic acid. 

 Whether /^-truxillic acid is formed from two mols. of rt//t>cinnaniic 

 acid or from one mol. of alio- and one mol. of ordinary cinnamic 

 acid (generated from «//t^cinnamic acid) will be further investigated. 



Physics. — "Isotherms of diatomic gases and of their binari/ 

 mixtures. VIII. Control measurements loith the volumenometer \ 

 By W. J. DE Haas. Communication N°. 121^ from the 

 Physical Laboratory at Leiden. ^Communicated by Pi'of. 

 Kamerlingh Onnes). 



(Communicated in the meeting of April 28, 1911). 



§ 1. Introduction. With a view to the determination of the com- 

 pressibility of hydrogen vapour, Prof. Kamerlingh Onnes invited me 

 to make a special study of the volumenometer (see Comm. N". 84) 

 with which these measurements were to be made ; the results of 

 this particular investigation are given in the present paper, and, at 

 the same time I have described the improvements mentioned in 

 Comm. N°. 117 which were specially introduced for the measure- 

 ment of the compressibility of hydrogen vapour, and to which 



