90 THE LACTIC ACID GROUP. 



salt must then be decomposed by sulphuretted hydrogen, and the 

 fluid concentrated, first by warmth, and afterwards in vacua : the 

 hydrated lactic acid is finally obtained in a state of purity by solu- 

 tion in ether. 



Liebig* prepares lactic acid from the juice of flesh, in the fol- 

 lowing manner. Flesh from which the fat has been most carefully 

 removed, is very finely chopped, repeatedly kneaded with water^ 

 and exposed to strong pressure ; the fluid thus obtained is heated 

 till it boils, filtered to remove the coagulated matters, decomposed 

 with baryta-water, again filtered, and very strongly concentrated by 

 evaporation. In the course of a few days the creatin crystallises ; 

 the milky liquid poured away from these crystals is rather more 

 strongly concentrated ; and then gradually treated with small por- 

 tions of alcohol, which causes the crystallisation of the inosinates 

 of baryta and potash. The mother-liquid, after the separation of 

 the inosinates, is evaporated, and the residue extracted with 

 alcohol ; after this alcoholic extract has stood for a considerable time 

 crystals are formed from it, while nearly pure lactate of potash 

 remains in the mother-liquid. To this we must add sulphuric acid 

 or a solution of oxalic acid (containing one-third of the acid), and 

 then precipitate the sulphate or oxalate of potash by means of 

 alcohol. The fluid filtered from the potash-salt is treated with 

 ether, as long as any precipitation continues ; the solution is then 

 evaporated to a syrup, and treated with half its volume of spirit 

 and five times its volume of ether, which takes up nearly pure 

 lactic acid. 



From this we may prepare lactate of lime, whose spirituous 

 solution must be purified by animal charcoal, and evaporated, so 

 that the salt may crystallise ; the lactic acid is then readily separated 

 from the lime-salt by sulphuric or oxalic acid with the aid of alcohol 

 and ether. 



Tests. To determine the presence of lactic acid is one of the 

 most difficult tasks in analytical animal chemistry, as is indeed 

 evinced by the prolonged contest that existed regarding the pre- 

 sence or absence of this acid in the animal organism. In order to 

 determine its presence with certainty, it must in the first place be 

 separated from all other organic substances, but in this lies one of 

 the great difficulties ; for there is scarcely any other acid to which 

 foreign bodies adhere so tenaciously. Liebig^s method (which 

 we have given) of preparing lactic acid from muscular juice is one 

 of the best means of separating this acid from animal fluids. If we 



* Ann. d. Ch. u. Pharm. Bd. 62, S. 312. 



