216 COAL-TAB COLORS USED IN FOOD PRODUCTS. 



more complete destruction of organic matter is obtained. Break up 

 the charred mass, introduce into a 200-cc graduated flask with about 

 100 to 150 cc of hot water, and add an excess of potassium perman- 

 ganate to oxidize sulphids. Destroy the excess of permanganate by 

 adding sulphur dioxid solution until the red color changes to brown, 

 then cool the mixture and make up to the mark with water. Filter 

 through a dry paper, acidify 100 cc of the nitrate with nitric acid, 

 and precipitate the chlorin as silver chlorid by the addition of silver 

 nitrate. If the solution should be brownish from a trace of organic 

 matter the silver chlorid does not readily coagulate and tends to pass 

 through the filter. In this case a few drops of potassium permanganate 

 solution are added to this acid mixture, the organic matter being 

 almost instantly oxidized. The mixture is then decolorized with a 

 few drops of sulphur dioxid solution, the silver chlorid is separated on 

 a tared gooch, washed, ignited, and weighed in the usual manner. 

 The following method may also be used for Ponceau 3R: 

 Dissolve 5 grams of the dye in 15C cc hot water, wash into a 250-cc 

 graduated flask, and add 25 cc of a 10 per cent solution of barium 

 nitrate. Cool the mixture, make up to the mark, and filter through a 

 dry paper; acidify 100 cc of the filtrate, representing 2 grams of color, 

 with nitric acid, and treat with silver nitrate solution, the precipi- 

 tated silver chlorid being separated, washed, ignited, and weighed in a 

 tared gooch crucible in the usual way. 



SODIUM SULPHATE. 



Dissolve 2 grams of dye in 100 cc of hot water, wash into a 200-cc 

 graduated flask, add 50 grams of pure sodium chlorid, cool, and make 

 up to the mark with water. Filter through a dry filter, dilute 100 cc 

 of the filtrate to 300 cc, acidify with hydrochloric acid and precipi- 

 tate the sulphates with barium chlorid. Filter, wash, ignite, and 

 weigh in a tared platinum gooch in the usual way. 



HEAVY METALS. 



Determine as given under Naphthol Yellow S, page 212. 



ARSENIC. 



Determine as given under Naphthol YeUow S, page 212. 



ETHER EXTRACTIVES. 



Determine as given under Naphthol Yellow S, page 214. 



SULPHATED ASH. 



Determine as given under Naphthol Yellow S, page 214. 



