CHANGES DURING THE SPOILAGE OF TOMATOES. 13 



(9) To 0.010 gram of lactic acid in 20 cc of water were added 0.5 

 gram of sodium hydrate and a slight excess of potassium permanga- 

 nate, the solution being heated on the steam bath for 10 minutes; 

 the excess of permanganate was decomposed with hydrogen peroxid, 

 the manganese dioxid filtered off and the filtrate made faintly acid 

 with acetic acid, the oxalic acid being precipitated as calcium oxalate 

 by the addition of calcium acetate. A strong precipitate of calcium 

 oxalate was obtained. By the same procedure and careful working 

 with small volumes, it was possible to obtain this calcium oxalate 

 precipitate with 1 mg of either lactic or malic acid. A control oxi- 

 dation in which only acetic acid was used gave no reduction of per- 

 manganate and no calcium oxalate. 



Experiments 1, 2, and 3 prove that in alkaline solution lactic acid 

 is oxidized quantitatively to oxalic acid by potassium permanganate 

 solutions. 1 Experiment 4 proves that it is necessary to have present 

 more than enough alkali to form the salt of lactic acid 2 and experi- 

 ments 5, 6, and 7 show that any method of determining lactic acid in 

 acid solution, such as that of Jerusalem, 3 would demand a very rigid 

 adherence to certain conditions to obtain comparable results, and 

 hence is of doubtful value for routine work. 



With reference to the detection of lactic acid the much used Uffel- 

 mann test 4 does not seem to be wholly reliable, as the same reaction 

 is obtained with oxalic, tartaric, succinic, and citric acids. The 

 method of detection proposed by Herzog, 5 which depends on the 

 reaction 



CH 3 CHOHCOOAg+ I 2 ^CHOHCOOH +CH 3 CHO + CO 2 +2AgI, 



the acetaldehyde being detected by known reactions, was found to 

 be more satisfactory for qualitative work than the Uffelmann test. 



THE BEHAVIOR OF MALIC AND TARTARIC ACID TOWARD OXIDIZING 



AGENTS. 



(1) Used 10 cc of 1 per cent malic acid, 3 grams of potassium hy- 

 droxid, and 120 cc of potassium permanganate solution (69 cc = 0.5 

 gram of malic acid) ; proceeded as under alkaline oxidation of lactic 

 acid; found 96.4 per cent of the theoretical amount. 



(2) Proceeded exactly as in No. 1 except that 8 grams of potassium 

 hydroxid were used; found 99.6 per cent of the theoretical amount 

 present. 



(3) Used 10 cc of 1 per cent malic acid as in No. 1; found 0.1063 

 gram of malic acid instead of 0.100 gram. 



1 Ulzer and Seidel, Monatshefte fur Chemie, 1897, 18: 138. 



2 Denis, Amer. Chem. J., 1907,38:561. 

 sfiiochem. Zts., 1908, 12:361. 



* Futh and Lochermann, Chem. Centrbl., 1906, 77(1) : 1452; ibid, 77(2) : 1087; Pharm. Ztg., 1910, 55:120. 



* Ann. Chem. (Liebig), 1907, 351 : 263. 



