CANNED VEGETABLES. 61 



under "XIII. Wine," paragraphs 12 and 13, page 85. Express fixed acids 

 as citric (1 cc of tenth-normal alkali equals 0.0070 grain of citric acid). Ex- 

 press volatile acids as acetic (1 cc of tenth-normal alkali equals 0.0060 gram of 

 acetic acid). 



4. Detection of Saccharin. 

 Proceed as directed under " XXVII. Food Preservatives," page 182. 



5. Detection of Preservatives. 



Proceed as directed under " XXVII. Food Preservatives," page 179. 

 6. Detection of Coloring Matters, 

 (a) IN TOMATOES AND CATSUPS. 



Extract the color from the dried pulp with alcohol, after acidifying with 

 hydrochloric acid, and filter. Eosin gives a characteristic fluorescent filtrate. 

 Dilute the filtrate with water, extract with amyl alcohol, and make dyeing tests. 

 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. (See also p. 190 under "XXVIII. Coloring 

 Matter.") 



(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 "7. Heavy Metals," following), trans- 

 fer the ash to a beaker, and treat with nitric acid; filter, make the filtrate 

 alkaline with ammonium hydroxid, 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 ferrocyanid. 



(c) IN MIXED PICKLES, ETC. 



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

 "XXVIII. Coloring Matter" (p. 199). 



7. Heavy Metals, 

 (a) ALLEN'S METHOD MODIFIED.** 



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. 

 Ignite over a Bunsen burner or, preferably, in a muffle, 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 the end to com- 

 plete the operation. Add about 50 cc of hydrochloric acid (1:3) and heat to 

 boiling or upon a steam bath for a half hour. Nearly neutralize the acid with 

 sodium hydroxid, dilute to 150 cc with water, precipitate with hydrogen sul- 

 phid. and filter, after heating for a few moments upon a steam bath to facili- 



Bigelow and Munson, J. Amer. Chem. Soc. Proc., 1900, 22: 32. 



