URINE. 129 



of lead produces a slight turbidity, most probably arising from a 

 small quantity of some impurity. No precipitate is obtained 

 with nitrate of silver, and the mixture, after having been ren- 

 dered ammoniacal, is not altered by boiling. A solution of per- 

 chloride of iron, rendered neutral by ammonia, produces no pre- 

 cipitate. It differs, therefore, in this respect from hippuric acid. 



' ' The author has not yet been able to ascertain the composi- 

 tion of this acid, in consequence of the small amount which he 

 obtained from 50 Ibs. of urine. It amounted to about eight 

 grains, and was not perfectly white. But it was easy to prove 

 that it contained nitrogen in considerable quantity." 1 



Pettenkofer precipitates the alcoholic extract obtained from 

 carefully evaporated human urine, previously neutralized with 

 carbonate of soda, with a concentrated alcoholic solution of 

 chloride of zinc. A brown amorphous precipitate containing 

 zinc is soon thrown down ; but after standing for several hours, 

 small granular and rather hard crystals are deposited on the 

 sides of the glass, which gradually increase to such an. extent 

 as to form perfect incrustations. On collecting the amorphous 

 precipitate and the crystals on a filter, and boiling with a suf- 

 ficient quantity of water, the amorphous precipitate remains in- 

 soluble, while the crystals gradually dissolve. On evaporating 

 the aqueous solution a yellow crystalline residue is obtained, 

 which in many of its physical characters resembles lactate of 

 zinc. Under the microscope these crystals appear as very 

 beautiful four-sided prisms, with an oblique terminal surface. 

 They are with difficulty soluble in water, and are insoluble in 

 strong alcphol and ether. In the aqueous solution we may de- 

 tect chlorine, zinc, and an organic substance very rich in 

 nitrogen. Repeated boiling with strong alcohol, or washing 

 with cold water, removes all the salts (chiefly metallic chlorides) 

 attached to the crystals, and if they are then again dissolved in. 

 water and heated with hydrated baryta, the oxide of zinc is pre- 

 cipitated, and carries with it the greater part of the adhering 

 colouring matter. The oxide of zinc and the excess of baryta 

 are then removed as carbonates by passing a stream of carbonic 

 acid through the solution; the filtered liquid which contains 

 chloride of barium and the organic substance is evaporated 



1 Poggendorff s Annalen, Ixxii, p. 602. 

 ii. 9 



