218 COAL-TAR COLORS USED IN FOOD PRODUCTS. 



SODIUM SULPHATE. 



Dissolve 1 gram of dye in 100 cc water contained in a 200-cc grad- 

 uated flask and treat the solution with 60 cc of a 20 per cent solution 

 of potassium chlorid. Make the mixture up to the mark with 

 water, shake, filter through a dry paper, dilute an aliquot of 100 cc 

 of the filtrate to 200 cc, acidify with 1 cc of 10 per cent hydro- 

 chloric acid, treat with 5 cc of 10 per cent barium chlorid solution, 

 and allow to stand over night. If a precipitate has been formed 

 this is separated, ignited, and weighed in the usual way. 



HEAVY METALS. 



Determine as given under Naphthol Yellow S, page 212. 



ARSENIC (SEEKER AND SMITH'S METHOD). 



Dissolve 2 grams of dye in a mixture of 130 cc water and 70 cc of 

 95 per ce"nt alcohol. 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 and add, from 

 a pipette, 20 cc of a sodium phosphate solution containing 100 

 grams of crystallized sodium phosphate per liter, after which mag- 

 nesia mixture (containing 55 grams of hydrated magnesium chlorid, 

 55 grams of ammonium chlorid, and 88 cc of ammonium hydroxid, 

 sp. gr. 0.9, per liter) is added from a burette, stirring vigorously. 

 The amount of magnesia mixture to be added should be in slight 

 excess of that necessary to precipitate the phosphate completely, 

 and should be previously ascertained by a blank experiment. Finally 

 add 10 cc of ammonium hydroxid (sp. gr. 0.96) and allow the whole 

 to stand for at least eight hours. Separate the precipitate by nitra- 

 tion and wash it free, or nearly so, of dye with a mixture of one-third 

 alcohol and two-thirds water containing one-tenth its volume of 

 ammonium hydroxid (sp. gr. 0.90). Dissolve the precipitate from the 

 paper with 20 per cent sulphuric acid, the washings being collected 

 in a large porcelain crucible. Add 5 cc of concentrated nitric acid 

 to the contents of the crucible and evaporate the whole almost to 

 dryness. The mixture need not be colorless at this point, a brown 

 colored solution giving equally accurate results. Add 20 cc of water 

 to the residue in the crucible and then 10 cc of a saturated solution 

 of sulphur dioxid. Evaporate the solution to a syrupy consistency 

 to remove sulphur dioxid, and then take up in 20 cc of water, place 

 in a 30-cc evolution bottle, add 5 cc of concentrated sulphuric acid, 

 and determine the arsenic by the modified Gutzeit method as given 

 under Naphthol Yellow S, page 213. 



ETHER EXTRACTIVES. 



Determine as given under Naphthol Yellow S, page 214 



