222 COAL-TAB COLORS USED IN FOOD PRODUCTS. 



SULPHUR. 



Determine as given under Naphthol Yellow S, page 215. 



NITROGEN. 



Determine on 2-gram portions by Gunning's modification of the 

 Kjeldahl process, using a little copper sulphate to assist the oxidation 

 (see page 7, Bulletin 107, Revised, Bureau of Chemistry, United 

 States Department of Agriculture). 



ERYTHBOSIN. 

 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. 



Dissolve 5 grams of the dye in 400 cc water and acidify with dilute 

 nitric acid. Make the mixture up to 500 cc with water, and then 

 filter through a dry filter. Determine chlorids in an aliquot of 200 cc 

 of the filtrate by precipitation with silver nitrate, washing, igniting, 

 and weighing the silver chlorid in a tared gooch crucible in the usual 

 manner. 



SODIUM SULPHATE. 



Employ another aliquot of the filtrate obtained after precipitating 

 the color acid as above in the determination of sulphates, precipi- 

 tating the latter as barium sulphate in the usual manner. 



HEAVY METALS. 



Determine as given under Naphthol Yellow S, page 212. 

 ARSENIC (SEEKER AND SMITH'S METHOD). 



Dissolve 16 grams of dye in 370 cc of water, add 5 cc of strong 

 bromin water, and finally 25 cc of dilute sulphuric acid (1 to 4). 

 Shake thoroughly and filter through a dry filter. Place an aliquot 

 of 250 cc, representing 10 grams of color from the filtrate, in a porce- 

 lain casserole, add 5 cc concentrated nitric acid (very important to 

 prevent loss of arsenic) , and evaporate till fuming has ceased. Reduce 

 the residue with sulphur dioxid solution, evaporate to small bulk, 

 and determine the arsenic in the form of apparatus used by Bishop in 



