52 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



8. DETECTION OF COLORING MATTERS. 

 (a) IN TOMATOES 11 AND CATSUPS. 



Most of the coloring matter used in tomatoes is either of coal-tar origin or 

 cochineal, and the general methods given under Coloring Matter (p. ) maybe 

 applied in these cases. Extract the color from the dried pulp with ordinary alcohol 

 after acidifying with hydrochloric acid and filter. Eosin gives a characteristic fluo- 

 rescent filtrate. Dilute the filtrate with water, extract with amyl alcohol and 

 dye. Cochineal if present is in the form of a lake and will require strong hydro- 

 chloric acid to decompose it. After extraction with amyl alcohol it may be tested 

 with uranium acetate (p. 120). 



(b) IN PEAS, BEANS, GHERKINS, ETC. 



Copper salts are most commonly employed in this class of goods, although it is 

 said that zinc is occasionally used. For the qualitative detection, ash from 15 to 20 

 grams of the sample, either with or without previous treatment with concentrated 

 sulphuric acid (see Heavy Metals below), transfer the ash to a beaker and treat 

 with nitric acid; filter, make the filtrate alkaline with ammonia, and if a precipitate 

 forms filter again. Copper will be indicated by the blue color of the filtrate. If 

 further test is desired acidify with acetic acid, and add potassium ferro-cyanide. 

 Red coloration or precipitate verifies the test. 



(c) IN MIXED PICKLES, ETC. 



Turmeric is frequently used and may be identified by the method given under 

 Coloring Matter (p. 120). 



9. DETERMINATION OF TOTAL AND VOLATILE ACIDITY. 



It is occasionally desirable to determine total acidity in tomatoes and catsups, and 

 volatile acidity in the latter. For this purpose use methods described under Fer- 

 mented and Distilled Liquors (p. 83). Express fixed acids as citric; one 1 cc of 

 decinormal alkali equals .0070 gram of citric acid. Express volatile acids as acetic; 

 1 cc of decinormal alkali equals .0060 gram of acetic acid. 



10. DETERMINATION OF HEAVY METALS. 



Owing to the almost universal presence of tin, the frequent occurrence of lead and 

 zinc, and the extensive use of copper as a coloring agent in this class of food materials, 

 the determination of heavy metals is of particular value. The method described by 

 Allen b and modified by Bigelow and Munson, has been used in the laboratory of 

 the Bureau of Chemistry for the determination of heavy metals in canned meats, 

 and may be applied as well to vegetables. Since the work on canned meats, how- 

 ever, the writer has worked out a method that for accuracy and ease of manipulation 

 is preferred to the modified Allen's method. 



(a) ALLEN'S METHOD, MODIFIED BY BIGELOW AND MUNSON. C 



Treat 100 grams of the moist material, or 25 grams of the dried material, with 

 about 5 cc of concentrated sulphuric acid and 2 cc of nitric acid. After foaming has 

 ceased add 3 grams of magnesium oxid and mix thoroughly. Then ignite over a 

 Bunsen burner or, preferably, in a muffled furnace, until thoroughly charred. Grind 

 in a mortar, and again ignite to complete combustion. The addition of a few drops 

 of nitric acid may be necessary toward t"he end to complete the operation. Add 



Girard and Dupre. Analyses des matieres nlimentaires.etc. 

 b Allen's Coin. Organic Anal. 3d ed. Vol. IV, p. 299. 

 Jour. Ainer. Chcin. Hoc. Proc. 1900, 22, 32. 



