DETERMINATION OF OXYBUTYRIC ACID 449 



termination of acetone, if glucose be present in the urine, 

 special care should be taken, because in heating sugar-con- 

 taining solutions substances of the nature of ketones and 

 aldehydes are easily produced which may be confused some- 

 times with acetone. 49 



Separation of acetone and diacetic acid, as elaborated by 

 Embden and Schliep 50 and by Folin, 51 is performed by driv- 

 ing over the preformed acetone in a given amount of urine 

 by careful distillation at very low pressure and temperature 

 (not above 35 C.), or by an air current, and estimating it. 

 Another portion of urine is subjected to the Messinger 

 method, after boiling with phosphoric acid, the diacetic acid 

 being thus converted into acetone; by which measure the 

 total of acetone and diacetic acid is obtained. Rowald 52 

 recommends a combination of Embden 's vacuum distillation 

 with the method of precipitation by nitrophenylhydrazine as 

 the most practicable means of separate determination of 

 acetone and diacetic acid. 



Quantitative Determination of Oxybutyric Acid. There 

 are essentially four methods available for quantitative de- 

 termination of oxybutyric acid : polarimetric estimation, con- 

 version into crotonic acid, into diacetic acid and into acetone. 



The polarimetric method worked out by Magnus-Levy, 

 depending upon the optical activity of oxybutyric acid and 

 yielding excellent results when large amounts are present, is 

 not reliable when one is dealing with small quantities, be- 

 cause of laevogyrating substances which can be obtained 

 even from normal urine in ether extraction, and because the 

 specific rotating power of /?-oxybutyric acid is not high. 53 



Darmstadter proposed a method by which the oxy- 



49 Borchhardt (Wiesbaden), Hofmeister's Beitr., 8, 62, 1906. 

 60 L. S'chliep (Embden's Lab.), Centralbl. f. Stoffw., No. 2, 250, 289, 1907. 

 61 0. Folin, Jour, of Biol. Chem., 3, 177, 1907; J. S. Hart, Jour, of Biol. 

 Chem., 4, 473, 1908. 



52 J. Rowald, Inaug. Dissert., Giessen, 1908. 



53 Embden and Schmitz, Geelmuyden, B. O. Przibram, Zeitschr. f. exper. 

 Pathol., 10, 279, 1912. 



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