CHANGES DURING THE SPOILAGE OF TOMATOES. 9 



procedure for the qualitative detection of citric acid. To 50 cc 

 of milk add 75 cc of water and 50 cc of Deniges reagent and 

 make up to 200 cc. Heat to boiling, and after removing the heat 

 add drop by drop 1 per cent of potassium permanganate solution 

 until the yellow precipitate quickly settles and the fluid clears. 

 Boil and then add hydrogen peroxid to remove the excess of per- 

 manganate. Filter and weigh. The weight of the precipitate 

 times 0.271 equals citric acid. This procedure was tried a number 

 of times, both exactly according to directions and with different 

 modifications, but the results were exceedingly unsatisfactory. 

 The formation of the acetone dicarbonic acid mercuric sulphate 

 complex was not quantitative under any conditions which were 

 tried. 



It seemed theoretically possible to dehydrate citric acid to give 

 acetone dicarbonic acid, which, either under the influence of gentle 

 oxidizing agents or simply by hydrolysis, might break down into 

 acetone and carbon dioxid, when the acetone could be distilled off 

 and estimated very exactly by the Deniges method. A large number 

 of experiments were made to test these suggestions, but the results 

 were unsatisfactory. While citric acid does break down in this 

 manner to a very large extent when treated with strong sulphuric 

 acid or with glacial phosphoric acid, or even with dilute sulphuric 

 acid and potassium permanganate, no conditions have yet been 

 found under which this reaction proceeds quantitatively. It was 

 found that the procedure of Beau was theoretically impossible as 

 some acetone dicarbonic acid would, in the presence of sulphuric 

 acid and potassium permanganate, break down into acetone, which 

 forms a quite different salt with mercuric sulphate from the one 

 formed by acetone dicarbonic acid, on which Beau bases his calcu- 

 lations. 



Determination of citric acid by the method of Spica 1 hi which citric 

 acid or a citrate is decomposed by sulphuric acid at 100 C. and the 

 evolved carbon monoxid gave satisfactory results with the gas appa- 

 ratus devised by the authors, 2 as is shown by the f ollowing data : 



0.36 grain of citric acid gave 44.0 cc of carbon monoxid at 27 C. and 766 mm, equiva- 

 lent to 39.1 cc at 760 mm and C., which equals 0.367 gram of citric acid or a recovery 

 of 101.9 per cent, 



0.248 gram of citric acid gave 29 cc of carbon monoxid at 21 C. and 772 mm, equiva- 

 lent to 0.250 gram of citric acid, a 100.8 per cent recovery. 



LACTIC ACID DETERMINATIONS. 



The method proposed for the determination of lactic acid in 

 ketchup and similar products is as follows: 



To 100 grams of ketchup add 10 cc of 20 per cent normal lead acetate, make up to 

 500 cc, shake well and centrifuge. To 400 cc of the clear portion add a moderate excess 



i Chem. Ztg., 1910, 34 : 1141. * U. S. Dept. Agr., Bureau of Chemistry Cir. 80. 



