HANDBOOK FOR BIO-CHEMICAL LABORATORY. 39 



be purified by recrystallization from, boiling water or from 

 ammouiaciil water. 



2. A large quantity of well-boiled fibrin is digested at 

 40 C. with a solution of Killings dried pancreas containing 1 

 per cent salicylic acid and some thymol. After a day or two 

 the liquid is filtered, faintly acidified with acetic acid, and 

 boiled. After filtration concentrate the filtrate nearly to 

 syrupy consistency and set aside to cool. Considerable quan- 

 tities of leuciu and tyrosin will have crystallized out after 24 

 hours. Remove the crystals and concentrate the mother-liquor 

 further if necessary, and precipitate the peptones with an 

 excess of hot alcohol, and filter while hot. On cooling crystals 

 of leucin will form if much is present. Pour oft the mother 

 liquor, and wash with a saturated solution of ammonium sul- 

 phate. The mixed leucin and tyrosin resulting from these 

 operations must be separated and purified by the method of 

 Hlasiwetz and Habermann, as described in method No. 1. 



The leucin may be simplest separated from the tyrosin by 

 boiling the yellow crystalline masses or crusts with alcohol, 

 which dissolves the leucin and leaves the tyrosin in great part. 

 After filtering and concentrating the filtrate leucin crystal- 

 lizes out and is purified by repeated crystallization from 

 alcohol. Tyrosin is obtained in a crystalline form by dissolv- 

 ing the residue insoluble in alcohol with water containing 

 ammonia, and allowing this solution, after filtration, to evap- 

 orate at ordinary temperatures. 



Properties. Leucin crystallizes when pure in shining 

 white, very thin, doubly refractive plates, nodular masses or 

 balls, possessing a greasy feel and which float on water. Pure 

 leucin dissolves in 27 parts cold water, and in 1040 parts cold 

 and in 800 parts boiling alcohol, though the solubility seems 

 to vary with the source of the leucin. On slowly heating it 

 melts at 170 C., and sublimes in white, woolly flakes, which 

 are similar to sublimed zinc oxide. Its specific rotatory power 

 is (a) D = -j- 17.5. Solutions of letiein in water are not, as a 



