212 COAL-TAB COLORS USED IN FOOD PRODUCTS. 



and then filter through dry paper. Treat 100 cc of the nitrate (repre- 

 senting 0.5 gram of dye) with 5 cc of 10 per cent barium chlorid solu- 

 tion without acidifying, and allow to stand overnight. If a precipi- 

 tate forms, it is filtered, washed, ignited, and weighed in the usual 

 way. 



HEAVY METALS. 



Treat the sulphated ash from 1 gram of the sample with 20 cc of 

 water, digest with ,10 cc of 10 per cent hydrochloric acid till solution 

 is complete, place 3 cc of the mixture in a test tube, add 10 cc of freshly 

 prepared hydrogen sulphid test solution (U. S. P.), shake the mixture, 

 warm to 50 C., stopper, and allow to stand in a warm place (at about 

 35 C.) for half an hour. Run a blank test at the same tune, with 

 the same amount of hydrogen sulphid solution, using water instead 

 of the solution containing the color ash. No turbidity other than 

 that sometimes produced by slight separation of sulphur should 

 appear in this test. Both tubes are then made slightly alkaline 

 with ammonium hydroxid, and no precipitate should be produced, 

 although a slight coloration, due to the presence of a small amount 

 of iron, sometimes occurs. If this coloration is very marked the 

 amount of iron should be determined. This is done by digesting the 

 sulphated ash from a weighed amount of the sample with hydrochloric 

 acid until all of the iron has gone into solution. The solution is 

 filtered, and the filtrate poured into an excess of hot, pure, freshly 

 prepared sodium hydroxid (by sodium) solution in a platinum dish. 

 The precipitate is washed, dissolved in dilute hydrochloric acid, and 

 again precipitated with ammonium hydroxid. The last precipitate 

 is washed, ignited, and weighed in the usual manner. 



ARSENIC (SEEKER AND SMITH'S METHOD). 



Dissolve 10 grams of the dye in 200 cc of water, heating to insure 

 complete solution of the color, add about 10 cc of strong bromin water 

 to convert any arsenite to arsenate. Make the mixture alkaline 

 with a few cubic centimeters of strong ammonium hydroxid. 

 Twenty cubic centimeters of a sodium phosphate solution containing 

 100 grams of crystallized sodium phosphate per liter are next added 

 from a pipette, after which magnesia mixture (containing 55 grams 

 of hydrated magnesium chlorid, 55 grams of ammonium chlorid, 

 and 88 cc of ammonium hydroxid, specific gravity 0.9 per liter) is 

 added from a burette, stirring vigorously. The amount of mag- 

 nesia added should be in slight excess of that necessary completely to 

 precipitate the phosphate and should previously be ascertained by 

 blank experiment. Then add 10 cc of ammonium hydroxid (specific 

 gravity 0.90), and allow the whole to stand for at least three hours; 

 separate the precipitate by filtration and wash it free, or nearly so, of 



