Chemical Constituents of the Animal Body. 225 



would yield, for example, glycine ethyl ester hydrochloride 

 of the formula CH 2 (NH 2 ) HC1 COOC 2 H 5 . This substance, 

 when glycine is yielded in relatively large quantity by the 

 hydrolysis, usually separates in a crystalline form when 

 the concentrated solution of the ester hydrochlorides in 

 alcohol (obtained after the third or fourth saturation of 

 the alcoholic solution with hydrochloric acid and sub- 

 sequent concentration) is cooled.* The free esters are 

 then generated from the hydrochlorides by the addition, 

 first of strong caustic soda solutions to the cooled syrup 

 until the excess of hydrochloric acid is neutralized, and 

 then of so much potassium carbonate till a pasty mass is 

 obtained. These operations are carried out in the presence 

 of large quantities of ether and with careful cooling by 

 ice. The hydrochloride is thus decomposed according, in 

 the case of glycine, to the equation 



2CH 2 .(NH 2 ) 2 -COOC 2 H 5 HC1 + K 2 C0 3 



= C0 2 + 2KC1 + 2CH 2 (NH 2 ) - COOC 2 H 5 



The free ester as it is formed passes into ethereal solution. 

 The latter is then dried, first by potassium carbonate 

 and then fused sodium sulphate, the ether is distilled off, 

 and the residue is then submitted to fractional distillation 

 under low pressure (0*5 mm.). 



The whole process of the separation of the mono- 

 amino-acids requires considerable care and experience, and 

 even then the separation of the various acids is by no 

 means completely quantitative. To obtain satisfactory 

 results, relatively large amounts of the protein under 

 investigation must be available. 



* When glutamic acid is present in quantity it separates in the form of its 

 hydrochloride when the hydrolysis mixture (produced by hydrochloric acid) is 

 concentrated for the purpose of esterification. The syrupy liquid is kept for 

 some time in a cold place, and the glutamic acid hydrochloride separates, and 

 is filtered off. The filtrate is then esterified with alcohol and hydrochloric acid 

 in the way described. 



(1,997) 15 



