18 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



stoppered with cotton, six to eight days at a temperature of 

 40, shaking the flask frequently. The cane-sugar will be 

 transformed for the most part into lactic acid, which com- 

 bines with the calcium. After the lapse of the time given 

 most of the chalk will be dissolved. Boil the mixture, filter, 

 concentrate to a small volume on the water-bath, and allow 

 to crystallize. The crystallized calcium lactate is dried by 

 pressing between drying-paper and purified by recrystallizing 

 from hot water, using some bone-black to decolorize if neces- 

 sary. The calcium salt is then converted into the zinc salt. 

 Determine the weight of the air-dried calcium salt and weigh 

 off the equivalent quantity of zinc sulphate (to 308 parts of 

 calcium lactate 287 parts of the crystallized zinc sulphate) 

 or a little less. Dissolve each salt in a little water, mix the 

 solutions, filter, after allowing to stand for some time, from 

 the calcium sulphate which separates, evaporate on the 

 water-bath, let stand till next day, and purify the zinc lac- 

 tate crystals obtained by recrystallization (microscopic 

 crystal form). From the zinc lactate we obtain the free 

 lactic acid by conducting hydrogen sulphide through its solu- 

 tion until the zinc is completely precipitated. The solution 

 filtered from the zinc sulphide is evaporated and the lactic 

 acid obtained is purified by dissolving in a mixture of equal 

 volumes of alcohol and ether (small quantity), filtering and 

 evaporating. 



The fermentation lactic acid, CH 3 CHOHCOOH (ordinary, 

 inactive, ethylidene, lactic acid), forms a colorless or pale- 

 yellow sirupy fluid of strong acid reaction, miscible in every 

 proportion with water, alcohol, and ether. 



For the lactic acid reaction of Uffelmann see the chapter 

 on Digestion. 



A part of the lactic acid obtained is used for the preparation of 

 pure zinc lactate. Boil with water and an excess of basic zinc car- 

 bonate, filter, and evaporate to crystallization (it is best to use the 



