52 THE CHEMICAL CONSTITUTION OF THE PROTEINS 

 Fraction IV. or Non-distilled Higher Boiling Esters. 



(c) Phenylalanine. 



The ester of phenylalanine differs from the esters of aspartic acid, 

 glutamic acid and serine, which are present with it in this fraction, by 

 being only slightly soluble in water. 



The mixed esters are dissolved in 5 volumes of water. If a 

 large amount of phenylalanine be present, it may separate in the form 

 of oily drops. The aqueous solution is extracted with an equal volume 

 of ether. The ether extract is then washed several times with water 

 to remove the last traces of any of the other esters which may have 

 been dissolved by the ether. The ether is removed by distillation and 

 the ester is hydrolysed by evaporation with concentrated hydrochloric 

 acid. The resulting phenylalanine hydrochloride is purified by crys- 

 tallisation from hydrochloric acid, and can be identified by an estima- 

 tion of its content in chlorine. 



The free amino acid is obtained from the hydrochloride by treating 

 with sodium acetate, or ammonia, and precipitating from hot aqueous 

 solijtion with alcohol. A determination of the melting-point of 283 

 and rotation of [a] D = - 35'i in aqueous solution characterises the 

 compound. 



(d) Aspartic Acid. 



The esters in the aqueous solution from which the phenylalanine 

 ester has been extracted with ether are saponified by boiling with 

 baryta ; the solution of baryta is prepared by/ dissolving twice the 

 quantity of barium hydrate to that of ester in sufficient hot water, 

 filtering and allowing to cool. The clear solution is poured off from 

 the crystals and to it is added the solution of esters. Hydrolysis is 

 then effected by heating for two hours on the water-bath. The solu- 

 tion is allowed to stand for several days to allow the barium salt of 

 racemic aspartic acid to crystallise out. 



The barium aspartate is decomposed with sulphuric acid, the 

 barium sulphate filtered off, and the excess of sulphuric acid quantita- 

 tively removed with baryta. Pure aspartic acid crystallises out from 

 the solution on evaporation. It is identified by analysis and by the 

 analysis of its copper salt. 



The remainder of the aspartic acid is isolated after removal of 

 glutamic acid as hydrochloride (e) as follows : 



The solution is evaporated in vacuo to remove as much hydrochloric 



