38 HANDBOOK FOR BIO-CHEMICAL LABORATORY. 



boiling it is diluted with water and gradually treated with 

 milk of lime with constant stirring until the liquid is neutral 

 or a little alkaline. Filter through a folded filter, the residue 

 on filter boiled with water several times, and after filtration 

 added to the main filtrates. The several filtrates are concen- 

 trated by evaporation and oxalic acid added so as to precipi- 

 tate all the lime; filter, boil the calcium oxalate precipitate 

 with water several times, filter and unite all filtrates, evapo- 

 rate until crystallization begins, and allow to cool. What first 

 crystallizes out consists chiefly of tyrosin with only a little 

 leucin. Filter this off and concentrate the liquid more, 

 when a second crystallization will form on cooling, which 

 consists of leucin with some tyrosin. This operation of evap- 

 orating and crystallizing is continued until no more crystals 

 are obtained. The several batches of crystals are united and 

 boiled with a large quantity of water and enough ammonia 

 to dissolve them. To this hot solution add lead acetate, con- 

 stantly stirring, until the precipitate formed is no longer 

 brown, but white; filter, heat the yellow filtrate to boiling, 

 neutralize or make faintly acid with dilute sulphuric acid, 

 filter while boiling hot, and allow to cool. Pure tyrosin is 

 deposited while leucin remains in solution. 



The mother liquor from the tyrosin is treated with H 2 S, 

 filtered and concentrated and boiled a couple of minutes with 

 freshly precipitated copper oxy hydrate. A deep blue solution 

 is the result, which, if filtered and concentrated, deposits sky- 

 blue crystalline warts, and an insoluble cuprous compound of 

 leucin. This precipitate, as well as the crystalline warts, is 

 decomposed in hot water with H 2 S, filtered, and the filtrate de- 

 colorized when necessary with animal charcoal, strongly concen- 

 trated, and allowed to crystallize. The leucin which deposits 

 may be purified by recrystallization from boiling alcohol or 

 by precipitating it as leucin lead oxide, decomposing this 

 precipitate when suspended in water with H 2 S, and evaporat- 

 ing the filtrate to point of crystallization. The tyrosin may 



