752 



As a third method he mentions that on lieating tiie «-acid above 

 its melting point the /i-acid is formed '). 



The first two methods, however, do not always give tiie desired 

 result, according to Erlknmkyer. He writes'): "In anderen Fallen 

 gelingt die Umwandlung aus noch nnbekannten Griinden selhst bei 

 ölïerer Wiederholnng nicht." 



The third method given l»_v him is not correct. Both the solidified 

 melt and the sublimate gave, on being illuminated, «-truxillic acid only. 



After various experiments I observed that the jï-acid is most 

 conveniently pi'epared by pouring an alcoholic solution of ft-cinnamic 

 acid, saturated at the ordinary temperature, in a large cpiantity of 

 water with stirring. On being illuminated this product always 

 yielded /i-truxillic acid only. 



/i'-cinnamic acid may be also olitained by allowing warm solutions 

 of cinnamic acid to crystallise. In this case the crystals are mostly 

 visible with the naked eye and the change into the «-acid can also 

 be traced. 



If, however, we make a saturated aqueous solution at boiling 

 heat, filter the same rapidly through cottonwool and filter off the 

 crystallisations at intervals, the succeeding fractions appear to be 

 different. The fraction depositing at a high temperature yields 

 «-cinnamic acid, whereas at a lower temperature iJ-cinnamic acid 

 crystallises (as proved by illuminating). 



Benzine and petroleum are very suitable licpiids for readily tracing 

 the transformation of the cinnamic acids. If we wish to prepare the 

 (i'-acid in this manner we must take care that the solution is not 

 too concentrated as otherwise plate-like crystals of «-cinnamic acid 

 will appear. The best thing is to cool locally (for instance the bottom 

 of the flask) a warm and not too strong benzene solution. Splendid 

 needles united in feathers are then formed. On these being left 

 undisturbed the crystals are seen to partly vanish, plate-like crystals 

 are formed and a few of the needles although retaining their original ^ 

 shape are seen to become transformed into a series of adjacent 

 plates which convey the impression that they were tacked with the 

 original needles. 



The lower the boiling point of the benzene and the greater the 

 concentration the more rapidly we notice the appearance of the 

 plates in addition to the little feathers. 



As to the transformation of the /?-"Storax" cinnamic acid into 

 the «-acid, Erlenmeyek also reports the following particulars. 



1) See also : Bioch. Zeitschr. 34, 356. (1911). 

 '-) Ber. 42, 509. (1909). 



