HIPPURIC ACID. 193 



Hippurate of copper, CaO.Hi+3HO, occurs in blue, oblique 

 rhombic prisms, and at 100 is anhydrous. 



Hippurate of lead., PbO.Hi, crystallises from hot solutions with 

 2 atoms of water in fine silky tufts of needles; from cold solutions, 

 by slow evaporation, in broad four-sided tablets, with 3 atoms of 

 water. At 100 it is anhydrous. 



Hippurate of silver, AgO.Hi + HO, occurs as a curdy preci- 

 pitate, which dissolves in boiling water, and, on cooling, separates 

 in beautiful silky needles. 



Hippurate of iron occurs as a dingy, voluminous precipitate, 

 which does not dissolve, but fuses in boiling water ; it dissolves in 

 warm alcohol, but falls as an amorphous precipitate on cooling ; it 

 crystallises from the cold solution in oblique rhombic prisms. 



Hippurate of oxide of ethyl, C 4 H 5 O.C 18 H 8 NO 5 , forms long, 

 white, silky needles, with a greasy feeling, devoid of odour, of an 

 acrid taste, slightly soluble in cold, but more so in hot water; it 

 fuses at 44, solidifying again at 32, and on exposure to a stronger 

 heat it decomposes. 



Products of its metamorphosis. The non-nitrogenous acid, 

 C 18 H 7 O 7 .HO, obtained from hippuric acid by the action of nitrous 

 acid, is, according to Strecker, readily soluble in ether, yields with 

 baryta a salt, crystallising in silky needles, and readily soluble in 

 water, and with oxide of silver a salt, AgO.C 18 H 7 O 7 , \vhich dis- 

 solves in boiling water, and on cooling crystallises in delicate 

 needles ; and which, on exposure to heat, developes hydride of 

 benzoyl. The production of this acid from hippuric acid is shown 

 in the equation C 18 H 8 NO5 + 3HO-H 3 N=C 18 H 7 O 7 .HO. 



Preparation. Hippuric acid is very easily obtained from the 

 urine of horses, but there is some difficulty in separating it from 

 the colouring matter. Fresh urine, obtained from horses, is 

 evaporated to -J-th of its volume, and then treated with hydrochloric 

 acid ; after it has cooled, the acid which has separated, and is 

 usually much discoloured, is dissolved in ten times its bulk of 

 boiling water, and boiled with milk of lime ; the solution is filtered, 

 a solution of alum is added till there is an -Acid reaction, and the 

 alumina is then precipitated by bicarbonate of soda. The boiling 

 with milk of lime destroys a portion of the pigment adhering to the 

 hippuric acid, while another portion of the pigment is precipitated 

 with the alumina. The acid precipitated by hydrochloric acid from 

 the filtered fluid is again dissolved in boiling water, boiled with 

 animal charcoal, and filtered while hot; on cooling, the acid now 



o 



