204 THE PRODUCTS OF ALBUMINOUS DIGESTION. 



can be obtained artificially by decomposing albuminous substances 

 with dilute mineral acids or alkalies. 



While impure tyrosin may occur in the form of spherules similar 

 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 bar.yta-water, 

 or it is laevorotatory 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-amino-benzoic acid, and 

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

 phenyl alanin. On bacterial decomposition it yields hydroparacu- 

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

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

 cresol, as has been shown (page 85). On fusion with caustic alkali, 

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

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



- /OH /OH 



C 6 H 4 ( + H 2 + O = C 6 H 4 < -f- CH 3 .COOH + NH 3 . 



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



On oxidation with potassium bichromate and sulphuric acid hydro- 

 cyanic acid, benzoic 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 rosin gives the well-known reaction of those albumins in which 

 a.'fomatic groups are present, but, as would be expected, in a degree 

 n ; uch more intense. The reaction is due primarily to the formation 

 o;P oxy-benzoic acid (salicylic acid). 



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

 centrated 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. Tyrosin-sulphonate of barium thus results, which gives 

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

 sesquichloride 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 



