98 PROPERTIES OF CERTAIN AMINO-ACIDS. [CH. IV. 



following exercise is suggested owing to the great prepon- 

 derance of leucine over tyrosine in the proteins employed. 



93. Preparation of leucine from blood. 



(i.) To i litre of defibrinated blood in a 2 litre flask, gradually 

 add 150 cc. of pure sulphuric acid, shaking well during 

 the addition. A semi-solid mass of coagulated protein is 

 obtained. 



(ii.) Heat on a boiling water bath for 12 to 16 hours, shaking 

 well at intervals. 



(iii.) Add some pieces of a broken porous pot, and heat to boiling 

 on a large sand bath. It is necessary to start with the 

 fluid hot from a water bath and to repeatedly shake the 

 mixture until it boils. Otherwise there is a risk of the 

 flask breaking. The mixture must be boiled for 10 to 

 14 hours. 



(iv.) To the hot fluid add a hot solution of baryta until the 

 mixture is alkaline to litmus. About 500 grams, of baryta 

 in about i J litres of boiling water are usually necessary, 

 (v.) Filter on a Buchner funnel. 



(vi.) Make the filtrate acid to litmus with dilute sulphuric acid. 

 Concentrate in a porcelain basin over a free flame to 

 about 500 cc. and filter. 



(vii.) Render the filtrate faintly alkaline to litmus by the 

 addition of ammonia and concentrate on a boiling water 

 bath until a crystalline crust has formed. Allow to cool 

 over-night. 



(viii.) Filter on a small Buchner funnel, pressing the mass of 

 crystals firmly with a pestle to remove as much of the 

 mother liquors as possible. The filtrate may be further 

 concentrated and a second crop of crystals obtained. 



(ix.) Recrystallise from 70 per cent, alcohol, as described in 

 Ex. 87, I. The product is apt to be contaminated with 

 isoleucine 



NH 2 NH 2 



( ^ " >CH.CH.COOH) and valine ( 3 ^ >CH.C1 

 \L 2 .H 5 -^ / \L,tl 3 ^ 



