80 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



2. The solution C decanted from the tyrosine is evaporated 

 further on the water-bath: crystals of leucine form on the 

 surface. These are to be examined under the microscope: 

 weakly refracting balls or aggregates, sometimes with a recog- 

 nizable radiating structure, which dissolve readily in hydro- 

 chloric acid and caustic alkalies. 



The solution is evaporated to a sirup, treated with several 

 times its volume of 90 per cent, alcohol, put into a flask, 

 heated on the water-bath to boiling, and, after it is perfectly 

 cold, filtered. The alcoholic extract contains a good deal of 

 leucine besides a little peptone; the insoluble residue, much 

 peptone with a small quantity of leucine. The alcoholic 

 extract is evaporated to dryness, the residue dissolved in 

 water, the solution boiled with lead hydroxide, and, after 

 cooling, filtered. The filtrate freed from lead by means of 

 hydrogen sulphide is filtered, evaporated to a small volume, 

 and the leucine, which separates on standing, dried on a clay 

 plate. 



Leucine, a-amino-isobutyl-acetic acid, (CH 3 ) 2 CHCH 2 - 

 CIi(NH 2 )COOH, is a constant cleavage product of albumin, 

 horn substance, gelatin, and tissues yielding gelatin, formed 

 by the action of dilute acids or alkalies and also on putrefac- 

 tion. It forms in pure condition shining white leaflets which 

 are wet by water only with difficultly. It dissolves in 40 to 

 46 parts of cold water, more readily in hot, and with diffi- 

 culty in alcohol, but is very much more readily soluble in 

 these solvents in the impure condition. 



Reactions of Leucine. 



(a) A little of the substance, when heated cautiously in 

 an open tube held slantingly, forms a woolly sublimate of 

 leucine; an odor of amylamine is evolved at the same time, 

 a part of the leucine undergoing decomposition. 



(6) Put a piece of caustic potash (stick form) about 1 cm. 



