224 COAL-TAR COLORS USED IN FOOD PRODUCTS. 



mixing, cover the vessel with a watch crystal, and add 10 cc of 

 nitric acid, keeping the dish covered. Agitate the mixture, place 

 on a steam bath, and keep covered until spattering ceases, after 

 which remove the watch glass and allow evaporation to proceed to 

 dryness. 1 Treat the residue with 5 cc of 7 per cent potassium per- 

 manganate and 5 cc of concentrated nitric acid and again evaporate 

 to dryness. Then add about 50 cc of water and 5 cc of concentrated 

 nitric acid to the residue, following this by 40 cc of a saturated solu- 

 tion of sulphur dioxid, and allow the whole to stand with occasional 

 stirring (breaking up the lumps with a glass rod) until the hydrated 

 oxid of manganese has dissolved. Filter, and wash the paper with 

 water. Add an excess of silver nitrate to the filtrate, and boil until 

 sulphur dioxid has been expelled and the silver iodid has flocculated. 

 Separate, wash, and weigh the precipitate in the usual manner. 



TOTAL HALOGENS. 



Mix 0.5 to 1 gram of the dye with 4 grams of potassium carbonate, 

 moisten to a paste, again thoroughly mix, cover with a layer of dry 

 potassium carbonate, dry, and ignite at a low red heat. Break up 

 the char thoroughly, digest with about 200 cc water, and filter. 

 Wash the insoluble matter until the washings no longer react with 

 silver nitrate; then acidify the filter and washings with nitric acid 

 and precipitate the halogens in the usual way as silver salts. 



INDIGO DISULPHOACID. 

 MOISTURE. 



Determine as given under Ponceau 3R, page 215. 



TOTAL INSOLUBLE MATTER. 



Determine as given under Naphthol Yellow S, page 211. 



NONVOLATILE OR INORGANIC INSOLUBLE MATTER. 



Determine as given under Naphthol Yellow S, page 211. 



SODIUM CHLORID. 



Determine as given under Ponceau 3R, page 215. 



SODIUM SULPHATE. 



Dissolve 2 grams of the dye in about 160 cc of water and treat the 

 solution with 40 giams of pure sodium chlorid. After the salt has 

 dissolved, make up the volume to exactly 200 cc. Shake the mix- 



* In the operation of drying particular care should be observed to prevent access of reducing gases to the 

 mixture. 



