URINE. 127 



In the analyses of Lehmann, to which we shall presently re- 

 fer, the lactic acid is determined quantitatively in a large 

 number of cases. The following independent investigations of 

 Heintz and Pettinkofer are important, as offering a clue to the 

 real nature of the crystals assumed by Lehmann and other 

 chemists, to consist of lactate of zinc. 



In the observations of Liebig, quoted above, it is assumed 

 that as lactic acid is not destroyed by putrefaction, it cannot be 

 altered in putrefied urine. Heintz conceived that during the 

 putrefaction of the urine certain causes might prevail to cause 

 the destruction of the lactic acid, and in order to determine the 

 point he instituted the following experiment. 



" About fifty pounds of fresh urine, obtained from several 

 young healthy men, were first evaporated over a free fire, and 

 then in the water-bath ; the extract obtained exhausted with 

 alcohol, to which a sufficient quantity of dilute sulphuric acid 

 had been added. The acid solution was saturated with oxide 

 of lead, the precipitate filtered, the liquid much evaporated, and 

 the urea contained in this concentrated solution precipitated 

 with pure oxalic acid. A considerable quantity of oxalate of . 

 urea was obtained, which, after washing with water and re- 

 crystallization, separated in perfectly white, large crystals. The 

 liquid, separated by pressure from the urea, from which it was 

 now almost free, was evaporated to dryness, extracted with 

 alcohol, and effloresced oxalic acid added to the solution to re- 

 move the soda. The oxalate of soda was separated by filtration, 

 the filtered solution saturated with oxide of lead, and then pre- 

 cipitated with basic acetate of lead. The lead was removed 

 from the filtered liquid by sulphuretted hydrogen ; the filtered 

 solution was concentrated over the water-bath, and boiled with 

 hydrate of baryta, when a considerable disengagement of am- 

 monia resulted. The salt of baryta obtained in solution was de- 

 composed with sulphate of zinc, in such a manner that only a 

 slight excess of this latter remained in the solution. It was 

 then evaporated to a small volume, when some delicate micro- 

 scopic crystals separated, which were at first taken for lactate 

 of zinc, but on examination under the microscope they soon 

 proved to be distinct. The lactate of zinc, for instance, forms 

 needles with acute dihedral summits, while the crystals of the 

 zinc salt obtained from the urine have truncated terminal sur- 



