760 THE AROMATIC SERIES. [App. 



Tyrosin crystallises in exceedingly fine needles which are usually 

 collected into feathery masses. The crystals are snow-white, tasteless and 

 odourless, almost insoluble in cold water, readily soluble in hot water, 

 acids and alkalis, insoluble in alcohol and aether. If crystallised from 

 an alkaline solution tyrosin often assumes the form of rosettes composed 

 of fine needles arranged radiately. 



Tyrosin does not sublime by heating, but is decomposed with an 

 odour of phenol and nitrobeuzol. On boiling with Millon's reagent 

 it gives a reaction almost identical with, but much more marked than, 

 that for proteids (Hoffman's test). If tyrosin is treated on a watch- 

 glass with one or two drops of strong sulphuric acid, then diluted with 

 a little water, neutralised with calcic carbonate and the solution filtered, 

 a characteristic violet colour is obtained on the addition of a drop of 

 acid-free ferric chloride (Piria's test). 



Preparation. By means similar to those employed for leucin, the 

 separation of the two depending on their widely differing solubilities. 

 According to Kuhne's method 1 large quantities are easily obtained as 

 the result of pancreatic digestion. 



Hippuricacid. C 9 H 9 NO 3 . Or Benzoyl-glycin. C 2 H 4 (C 7 H 5 0)N0 2 . 



Is found in considerable quantities in the urine of herbivora, and 

 also, though to a much smaller amount, in the urine of man. It is 

 formed in the body by the union with dehydration of glycin and benzoic 

 acid, see p. 441. 



Crystallised from a saturated aqueous solution, it assumes the form 

 of fine needles ; if from a more dilute solution, white, semitransparent 

 four-sided prisms are obtained. These when pure are odourless, with a 

 somewhat bitter taste. They are soluble in 600 parts of cold water, 

 readily soluble in boiling water, readily soluble in alcohol, less so in 

 sether. All the solutions redden litmus. 



Hippuric acid is monobasic, and forms salts which are readily 

 soluble in water (except the iron salts); from these, if in sufficiently 

 concentrated solutions, excess of hydrochloric acid precipitates the acid 

 in fine needles. When heated with concentrated mineral acids it is 

 resolved into benzoic acid and glycin. The same decomposition occurs 

 in presence of putrefying bodies. Strong nitric acid produces an odour 

 of nitrobenzol. 



Preparation. Fresh urine of horses or cows is treated with milk of 

 lime, in order to form calcic hippurate and thus prevent the decom- 

 position of the hippuric acid, filtered, and the filtrate evaporated to a 



1 Op. cit. (sub Leucin). 



