14 CHANGES DURING THE SPOILAGE OF TOMATOES. 



(4) Used 1 cc of a 1 per cent malic acid solution, 3 grams of sodium 

 hydroxid, and enough potassium permanganate to produce a blue- 

 black color. Heated for 30 minutes on the steam bath, removed 

 excess of permanganate with hydrogen peroxid, and filtered. Deter- 

 mined the oxalic acid as calcium oxalate and found 0.190 gram of 

 oxalic acid (H 2 C 2 O 4 + 2H 2 O) instead of the calculated amount, 0.188 

 gram. 



(5) Used 20 cc of 1 per cent malic acid, just as in No. 3; found 

 0.3747 gram of oxalic acid in place of the calculated amount, 0.376. 



(6) Used 25 grams of 1 per cent malic acid, exactly as in No. 3; 

 found 0.475 gram of oxalic acid instead of 0.470 gram as calculated. 



(7) Samples Nos. 1, 2, 3, 4, 5, 6, each containing 10 cc of 1 per cent 

 malic acid, and, respectively, 5, 10, 15, 20, 25, and 30 cc of 10 per 

 cent sodium hydroxid solution and 20 cc of permanganate solution 

 (8.5 cc = 0.5 gram oxalic acid). Heated for fifteen minutes on a 

 steam bath, acidified with sulphuric acid and added to each sample 

 10 cc of 10 per cent oxalic acid. To titrate back required for No. 1, 

 7.8 cc; No. 2, 7.7; No. 3, 7.7; No. 4, 7.8; No. 5, 7.7; and No. 6, 7.7 cc 

 of this permanganate, respectively. Found 0.096 and 0.097 gram. 

 The variation of the amount and strength of the alkali within the 

 limits given has no effect on the course of the oxidation. 



When, however, the amount of alkali present is just sufficient to 

 neutralize the malic acid, the oxidation to malic acid does not take 

 place quantitatively, as is shown by the following experiments: 



(a) Used 10 cc of 1 per cent malic acid, just neutralized to phenol- 

 phthalein, with sodium hydrate ; oxidized with permanganate exactly 

 as in experiment 1. Found 0.058 gram instead of 0.100 gram. 



(6) Used 10 cc of 1 per cent malic acid just as in (a). Found 0.078 

 gram instead of 0.100 gram. 



The oxidation of malic acid in acid solution with potassium per- 

 manganate is very similar to, that with lactic acid; the reaction does 

 not yield carbon dioxid and water quantitatively as is shown by the 

 following experiments: 



(a) Used 10 cc of 1 per cent malic acid with 5 cc of concentrated 

 sulphuric acid, requiring 66 cc of potassium permanganate solution 

 (69 cc = 0.5 gram of oxalic acid) for oxidation to a pink color per- 

 manent for five minutes. Calculated for complete oxidation to carbon 

 dioxid and water, 77.8 cc. 



(6) Used 10 cc of 1 per cent malic acid and 10 cc of concentrated 

 sulphuric acid same strength as in (a). Required 59 cc of potassium 

 permanganate; calculated amount, 77.8 cc. 



Tartaric acid exhibits the same general behavior as malic and lactic 

 acids toward acid and alkaline permanganate solutions, as is shown 

 by the following experiments: 



(a) Used 10 cc of 1 per cent tartaric acid, 8 grams of sodium 

 hydroxid, and 20 cc of potassium permanganate solution (8.4 cc = 0.5 



