21 



GIFT _ 



U.NIV 



issued September 13, 1911 



United States Department of Agriculture, 



BUREAU OF CHEMISTRY Circular No. 76. 

 H. W. WILEY, Chief of Bureau. 



DETERMINATION OF MALIC ACID. 



By P. B. DUNBAB and R. F. BACON, Assistant C it enlists, Division of Foods. 



INTRODUCTION. 



The method described herein is based on the fact first observed by 

 Walden 1 that under certain conditions uranium salts produced a 

 very marked increase in the specific rotation of Z-malic acid. 

 Walden noticed that a similar but less marked effect is produced by 

 uranium salts on <#-tartaric acid, e?-methyl tartrate, Z-quinic, and 

 Z-mandelic acids, the increased rotation being in the same direction 

 as the rotation of the aqueous solution of the substance. He con- 

 cluded that the effect is limited to the active oxy-acids. As stated 

 by Walden, the requisites of an agent which is to be used for the 

 detection of malic acid by optical means are: (1) That the direction 

 of rotation shall be constant, and (2) that the increase in rotation 

 shall be as large as possible. This, of course, applies also to the 

 quantitative estimation of malic acid. In addition, the agent in 

 question should have little or no influence on any other substances 

 which may occur in conjunction with malic acid. It has long been 

 known that certain substances such as the oxygen compounds of 

 boron 2 arsenic, antimony, molybdenum, and tungsten 3 have the 

 power of increasing the specific rotation of the oxy-acids. Uranium 

 salts, however, are the only ones which fulfill the requirements just 

 stated with any degree of satisfaction. 



The authors have recently had the privilege of reading an article 

 by P. A. Yoder entitled "A Polariscopic Method for the Determina- 

 tion of Malic Acid and Its Application in Cane and Maple Prod- 

 ucts." 4 This paper was presented at the forty-second meeting of 



ifier. d. chem. Ges., 1897, 80 (3) : 2889. 



2 Biot, Mem. de 1'acad. roy. sci., 1838, 16: 229; Ann. chim. phys., 1884 (3), 11: 82; 

 1850, 29: 341, 430; 1860, 59: 229. Pasteur, Ann. chim. phys., 1860 (3), 59: 243. 

 8 Gernez, thr. Landolt's Optical Rotation of Organic Substances, tr. by Long, p. 248. 

 * J. Ind. Eng. Chem., 1911, 8: 563. 

 3123 Cir. 7611 



