cAY 
PERMITTED COAL-TAR FOOD DYES 15 
soluble matter, treat the crucible as follows: Wash with hot water, 
ignite, rewash, dry in an air oven at 135° C., cool in a desiccator 
containing calcium chloride, and weigh. Repeat until the weight 1s 
constant 
DETERMINATION 
For amaranth, erythrosine, naphthol yellow S, tartrazine, guinea 
green B, and light green S F yellowish.—Dissolve 5 grams of dye in 
200 c. c. of hot water and allow the solution to cool to room tem- 
perature. Filter through the prepared Gooch crucible and wash 
_ with cold water until al! the dissolved dye has been removed. Dry 
in an air oven at 135° C., cool in a desiccator containing calcium 
chloride, and weigh. Repeat the drying, cooling, and weighing 
until the weight 1s constant. 
For ponceau 3R, orange I, and indigotine—Dissolve 5 grams of 
dye in 250 c. c. of hot water and boil, with frequent stirring, for 
three minutes. Cool the solution to room temperature and let 
stand cold overnight. Filter with moderate suction. Wash with 
cold water, dry in an air oven at 135° C., cool in a desiccator contain- 
ing calcium chloride, and weigh. Repeat the drying, cooling, and 
weighing until the weight is constant. 
In both cases report the percentage increase in weight as total 
- water-insoluble matter. 
NONVCLATILE WATER-INSOLUBLE MATTER 
For ponceau 38R, amaranth, erythrosine, orange I, naphthol yellow S, 
tartrazine, guinea green B, light green S F yellowish, and indigotine.— 
Incinerate the Gooch crucible containing the total insoluble matter 
(p. 14) at a low red heat until all the organic matter has been volatil- 
ized. Cool in a desiccator containing calcium chloride and weigh. 
Report as nonvolatile water-insoluble matter. 
SODIUM CHLORIDE 
REAGENTS 
All reagents must be halogen free. 
Sulphur diozride solution.—Saturate ice-cold distilled water with 
sulphur dioxide. Keep the solution stoppered and in a cold place. 
DETERMINATION 
For ponceau 3R, amaranth, orange I, tartrazine, quinea green B, 
ie green S F yellowish, and indigotine—Thoroughly mix 5 grams 
dye with 4 to 6 grams of potassium or sodium carbonate in a 
50 c. c. platinum or nickel crucible and moisten with water or 50 
per cent alcohol. Cover evenly with about 1 gram of the powdered 
carbonate, dry, and ignite at a low red heat until all organic matter 
is destroyed. Allow to cool and add enough water to form a thin 
paste. With a glass rod break oP any lumps present, in order to 
produce a uniform suspension. Wash the mixture into a 250 ¢. ¢. 
 yolumetric flask with 100 to 150 c. c. of hot water and let stand 
until all soluble salts have dissolved and the mixture is cold. Dilute 
to the mark with water, mix thoroughly, and filter through a dry 
