910 



APPENDIX. 



insoluble in alcohol and ether. If crystallized from an alkaline solution tyrosin often 

 assumes the ibrm of rosettes composed of fine needles arranged radiately. 



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

 and nitrobenzol. On boiling with Millon's reagent it gives a reaction almost identi- 

 cal 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, neutralized with calcic carbonate, and the solution 

 filtered, a characteristic violet color 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 Kiihne's 

 method, 1 large quantities are easily obtained as the result of pancreatic digestion. 



Hippuric Acid. C 9 H 9 N0 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. 



Crystallized 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 [Fig. 255]. These when pure are odorless, with a somewhat bitter 



[Fio. 255. 



Hippuric Acid Crystals.] 



taste. They are soluble in 600 parts of cold water, readily soluble in boiling water, 

 readily soluble in alcohol, less so in ether. 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 pro- 

 duces an odor 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 decomposition of the hippuric 

 acid, filtered, and the filtrate evaporated to a small bulk ; the hippuric acid is then 

 precipitated by adding an excess of hydrochloric acid ; the acid is then purified by 

 several crystallizations from boiling water. 



When heated in a small tube, hippuric acid gives a sublimate of benzoic acid and 

 ammonic benzoate, accompanied by an odor like that of new hay, while oily, red 

 drops are observed in the tube. This is very characteristic and distinguishes it 

 from benzoic acid. 



1 Op. cit. (sub. Leucin). 



