10 BULLETIN 158^ U. S. DEPARTMENT OF AGEICULTUEE. 
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. 
Monoamino adds. — The filtrate from the phosphotungstic acid 
precipitate was made alkaHne with barium hydroxide in order to 
remove the sulphuric and phosphotungstic acids, and filtered. The 
filtrate was concentrated and nearly neutrahzed with sulphuric acid. 
This sUghtly 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 alcohohc solution was then filtered, the 
insoluble salts redissolved in water, and reprecipitated by pouring 
into alcohol as before. The alcohohc 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 sohd 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 boihng 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 resembhng 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 
J See Gulewitsch, Zeit. physiol, Chem., 27, 178 (1899). 
