450 ACETONE BODIES 



butyric acid is converted into crotonic acid by distillation 

 with sulphuric acid, with separation of water, and the 

 crotonic acid then determined by alkalimetry. This method, 

 however, has proved to be rather inexact in control tests ; 54 

 but apparently excellent results are obtained, according to 

 Ryffel 55 and B. 0. Przibram, 56 by determining the crotonic 

 acid, not by alkalimetry, but by taking advantage of its 

 ability to fix bromine : 



OXTBUTTRIC ACID CROTONIC ACID BROMINE ADDITION PRODUCT 



Crij C^rlj (_xij 



CH.OH CH CH.Br 



> > 



CHj CH CH.Br 



COOH COOH COOH. 



The bromine is added in excess ; the excess of bromine, 

 on the addition of potassium iodide, sets free an equivalent 

 amount of iodine which is estimated by titration with thiosul- 

 phate. It is recommended that the urine be not subjected 

 to direct sulphuric acid distillation, but that, saturated with 

 ammonium sulphate and acidulated with sulphuric acid, it 

 be first extracted for twenty-four hours with ether in Lindt's 

 apparatus and the ethereal extract further employed. 



A colorimetric method of estimating oxybutyric acid has 

 been proposed, depending upon transformation of oxy- 

 butyric acid into diacetic acid by hydrogen peroxide, and 

 subsequent estimation of the latter optically by the beautiful 

 red color which it yields on addition of ferric chloride. 57 In 

 view of the instability of diacetic acid, however, it is impos- 

 sible to restrain a feeling of distrust for this method. 



An excellent mode of determination, however, is afforded 

 in Schaffer's method, 58 which consists of heating to boiling 

 the fluid containing the oxybutyric acid, in the presence of 



M Embden and Sehmitz, B. O. Przibram, 1. c. 



65 Ryffel, Jour, of Physiol., 82, Proc. Physiol. Soc., LVI, May 20, 1905. 



M O. F. Black, Jour, of Biol. Chem., 5, 207, 1908. 



67 B. O. Przibram, 1. c. 



"P. A. Schaffer, Jour, of Biol. Chem., 5, 211, 1908. 



