METHOD OF LACTIC ACID DETERMINATION 455 



lactic acid in the extract obtained by boiling muscle can be 

 determined with great accuracy by titration (using phenol- 

 phthalein as indicator), because all the recognizable lactic 

 acid is present in free form, and the amount of other acid 

 products is of no practical importance; and the fraction of 

 lactic acid in the proteid coagulum can be released for de- 

 termination by liquefying the coagulum by heating with 

 caustic alkali, the albuminous fluid freed of its protein by 

 addition of saturated salt solution, and finally the lactic acid 

 determined by the method proposed by the author and 

 Charnass in the protein-free filtrate. 



Determination of Lactic Acid and $-oxyfbutyric Acids 

 Together. Recourse should also be had to a special method 

 for determination of lactic acid in case fluids containing both 

 lactic acid and /?-oxybutyric acids are to be dealt with. In 

 separate portions the two acids may be determined, respec- 

 tively, as aldehyde or acetone (v. sup.), after oxidation with 

 permanganate or with bichromate in a sulphuric acid solu- 

 tion. As in both cases, however, a mixture of aldehyde and 

 acetone distills over, separation of the two substances is 

 requisite. In estimating the lactic acid a modification is in- 

 troduced, whereby in an aliquot portion of the distillate the 

 readily destroyed aldehyde is decomposed by boiling with 

 hydrogen peroxide and potassium hydrate, the acetone re- 

 distilled and titrated according to Eipper. In estimating 

 the butyric acid the distillate (containing acetone and alde- 

 hyde) is freed of its aldehyde by boiling with hydrogen 

 peroxide and caustic potash ; the acetone is redistilled and 

 determined by titration according to Messinger's method. 7 



Ryffel's Method of Lactic Acid Determination. Byffel 

 proposed a method of lactic acid determination which de- 

 pends upon a somewhat different principle. In this the 

 lactic acid in the urine is broken up directly into acetaldehyde 



T J. Mondschein (under direction of 0. v. Fiirth), Biochem. Zeitschr., 42, 

 91, 1912. 



