310 GLYCOCINE. [BOOK II. 



The decomposition should be effected in the apparatus shewn in 

 fig. 20. One part of hippuric acid is boiled in it for 10 12 hours 

 with four times its weight of dilute sulphuric acid (1 of acid to 6 of 

 water, by weight). At the end of this time, the contents of the 

 flask are poured, with caution 1 , into a capsule, allowed to settle for 

 24 hours, and then filtered. The benzoic acid, which has separated 

 out, is washed with cold water, the filtrate is concentrated by 

 evaporation, and shaken with ether, so as to free it from all traces of 

 benzoic acid; the acid solution is then largely diluted and exactly 

 neutralised by means of barium hydrate (or by heating with barium 

 carbonate). The precipitate is allowed to settle, washed by de- 

 ca-ntation with boiling water, the filtrate concentrated by evaporation ; 

 in the event of an excess of barium hydrate having been added, C0 2 

 is passed through it, the liquid boiled and then filtered and 

 concentrated until crystals commence to form on the surface. 

 The liquid is then set aside to crystallise during 24 hours ; the 

 mother liquid is separated from the crystals and again concentrated, 

 the process being repeated so long as crystals continue to separate. 

 The glycocine thus obtained is purified by being recrystallised from 

 water 2 . 



s Glycocine may be synthetically obtained by various 



glycocine methods. The most interesting is perhaps by the 



action of ammonia on bromacetic acid or on chloracetic 

 acid, the reactions being shewn in the following equations : 



(1) CH 2 .Br.COOH + NH 3 = CH 2 .NH 2 .COOH + HB, 



(2) CH 2 .C1.COOH + 2NH 3 = CH 2 .NH 2 .COOH + NH 4 C1. 



Physical and Glycocine occurs in fine, hard, colourless, crystals, 



Pr " una ^ ere( i by exposure to air, and which present the 

 form either of rhombohedra or of four-sided prisms. 



FIG. 21. GLYCOCINE. 



1 Caution is needed to avoid spurting, as when the hot liquid is poured into the 

 capsule, the benzoic acid which had been in a melted (oily) condition suddenly solidifies, 

 and violent ebullition ensues. 



2 The description of this process is taken almost verbatim from Drechsel's Arilei- 

 tung zur Darstellung physiologisch-chemischer Praeparate, p. 9. 



