THE PRODUCTS OF TRYPT1C DIGESTION. 189 



to those of leucin, the pure substance crystallizes in delicate, silky 

 needles, which are often grouped in sheaves and rosettes. Accord- 

 ing to its mode of formation, the substance is optically inactive, as 

 when formed synthetically or by decomposition with baryta-water, 

 or it is Ia3vorotatory when derived from albumins on boiling with 

 acids. In cold water it is only slightly soluble, while in boiling 

 water it dissolves in the proportion of 1 to 154. Its solubility is 

 increased in the presence of alkalies or mineral acids. In alcohol 

 and ether it is insoluble. 



Tyrosin may be regarded as para-oxy-phenyl-propionic acid, and 

 has the formula C 6 H 4 (OH).CH 2 .CH(NH 2 ).COOH. It may be formed 

 synthetically from ethylene oxide and para-am ido-benzoic acid, and 

 can also be obtained from para-amido-phenyl alanin and para-nitro- 

 phenyl alanin. On bacterial decomposition it yields hydro paracu- 

 maric acid (para-oxy-phenyl-propionic acid), which can be further 

 transformed into para-oxy-phenyl-acetic acid, and this into para- 

 o-resol, as has been shown (page 89.) On fusion with caustic alkali, 

 on the other hand, it gives rise to the formation of para-oxy-benzoic 

 fccid, acetic acid, and ammonia, as is shown in the equation : 



/OH /OH 



C G H A / + H 2 + = C 6 H/ + CH 3 .COOH + NH 3 . 



\CH,.CH ( NH 2 ) .COOH \COOH 



On oxidation with potassium bichromate and sulphuric acid hydro- 

 cyanic acid, benzole acid, acetic acid, and formic acid result. 



With acids and alkalies, as also with certain salts of the heavy 

 metals, tyrosin combines with difficulty to form salt-like bodies. 



Tests for Tyrosin. HOFFMANN'S TEST. With Millon's reagent 

 tj msm gives the well-known reaction of those albumins in which 

 aromatic groups are present, but, as would be expected, in a degree 

 ir/uch more intense. The reaction is due primarily to the formation 

 o:F oxy-benzoic acid (salicylic acid). 



PIRIA'S TEST. A few crystals of tyrosin are dissolved in con- 

 contrated sulphuric acid and heated to about 100 C., when the sub- 

 stance dissolves. Tyrosin-sulphuric acid is thus formed, and gives 

 rise to a red color/ On cooling, the liquid is diluted, and treated with 

 barium carbonate while heating until the reaction becomes just 

 alkaline. Ty rosin-sulphate of barium thus results, which gives rise 

 to a dark-violet color on treating with a very dilute solution of 

 sesqnichloride of iron. An excess of iron, however, must be care- 

 fully avoided. Oxy-benzoic acid gives the same reaction. 



SCHERER'S TEST. On evaporating tyrosin with a few drops of 

 nitric acid on platinum foil a yellow, transparent residue is obtained, 

 which turns red on moistening the substance with a drop of sodium 

 hydrate solution, and becomes brown on further evaporation. The 

 reaction is due to the formation of nitro-ty rosin nitrate, but is not 

 characteristic, as other bodies behave in a similar manner. 



Isolation of Leucin and Tyrosin. To isolate leucin and tyrosin 



