10 BULLETIN" 158, U. S. DEPARTMENT OF AGRICULTURE. 



Arginine. — The method of isolating arginine is simply a further 

 step in the method used in the isolation of histidine. Arginine was 

 isolated first as the acid nitrate salt, which crystallized in the form 

 of plates/ and was further identified by preparing the neutral nitrate 

 salt and the copper nitrate salt both in characteristic crystalline 

 form. 



Monoamine) acids. — The filtrate from the phosphotungstic acid 

 precipitate was made alkaline with barium hydroxide in order to 

 remove the sulphuric and phosphotungstic acids, and filtered. The 

 filtrate was concentrated and nearly neutralized with sulphuric acid. 

 This slightly alkaline solution, about 500 c.c. in volume, was treated 

 by boiling with freshly prepared copper hydroxide, and was then 

 poured into about 3,000 c.c. of 95 per cent alcohol and allowed to 

 stand over night, in order that the insoluble mineral matter might 

 settle out. The deep-blue alcoholic solution was then filtered, the 

 insoluble salts redissolved in water, and reprecipitated by pouring 

 into alcohol as before. The alcoholic solutions were combined and 

 evaporated to dryness, the residue was taken up in hot water and 

 the copper removed by treatment with hydrogen sulphide. After 

 filtering from the copper sulphide, the solution, which contained 

 considerable color, was boiled with animal charcoal. The filtered 

 solution was made faintly alkaline with ammonia and treated with 

 freshly precipitated copper hydroxide, keeping the volume of the 

 solution at about 1,000 c.c. The solution was filtered from the 

 excess of copper hydroxide and evaporated to dryness on the steam 

 bath. The solid residue was then scraped from the sides of the 

 dish and extracted in a Soxhlet extractor with absolute methyl 

 alcohol until no further blue color was imparted to the alcohol. 



Leucine. — The alcohol insoluble portion was dissolved in a large 

 volume of boiling water and the copper removed with hydrogen 

 sulphide. The solution was filtered, boiled down to a volume of about 

 50 c.c. and treated with ammoniacal lead acetate until no further 

 precipitation took place. The precipitate was washed with 95 per 

 cent alcohol and was finally decomposed with hydrogen sulphide after 

 suspending in water. On concentration of a portion of this solution 

 the characteristic crystals of impure leucine formed. These crystals 

 separated in concentric nodules closely resembling fat, but which 

 were composed of concentrically grouped highly refracting needles. 

 These crystals were redissolved in water and added to the original 

 solution which was boiled up with animal charcoal until the color 

 disappeared. The leucine was then purified as before by the forma- 

 tion of the copper salt and the basic lead salt. On concentrating the 

 solution obtained from this purification, crystals of pure leucine were 

 obtained. These crystals formed in pearly scales, which somewhat 



i See Gulewitsch, Zeit. physiol. Chem., 27, 178 (1899). 



