PERMITTED COAL-TAR FOOD DYES 17 
When the mixture is dissolved remove and wash the crucible over the 
beaker. Neutralize the solution carefully with strong nitric acid, 
adding 1 to 3 c. c. in excess. Cool, transfer to a €-inch porcelain 
evaporating dish, and add 19 c. c. of 0.1 N silver nitrate solution 
and 5 to 10 ¢. c. of 10 per cent ferric alum solution. ‘Titrate the 
solution with 0.1 N ammonium or potassium thiocyanate, adding 
1 or 2 drops after the red end point has been reached. Add another 
cubic centimeter of silver nitrate, making 20 c. c. in all. Filter the 
solution through a Biichner funnel and wash the precipitate with a 
little water slightly acidified with nitric acid. Return the filtrate 
and washings to the evaporating dish and titrate to the end point 
with ammonium or potassium thiocyanate. Calculate to percentage 
of sodium chloride. 
SODIUM SULPHATE 
For ponceau 38R, amaranth, orange I, tartrazine, and indigotine.— 
Transfer to a 250 c. c. volumetric flask that volume of the master 
solution which contains 5 grams of the dye. Add water, if neces- 
sary to bring the volume to 200 c.c., and heat on a steam bath. Add 
pulverized sodium chloride free from sulphates as follows: For ama- 
ranth and tartrazine, 70 grams; for ponceau 3R, orange I, and indigo- 
tine, 50 grams. Stopper the flask and shake at frequent intervals for 
an hour. To hasten the precipitation the solution may be cooled in 
ice water. Dilute to the mark with saturated sodium chloride solu-- 
tion, shake, and filter on a dry 18 cm. paper. To 100 c. c. of the 
filtrate add 200 c. c. of water and 1 c. ce. of hydrochloric acid (1+9). 
Heat to boiling and add a slight excess of hot 10 per cent barium 
chloride solution. Allow to stand overnight and filter through a 
weighed Gooch crucible. Wash the precipitate of barium sulphate 
thoroughly with hot water, ignite, cool in a desiccator containing 
calcium chloride, and weigh. Calculate the percentage of sodium 
sulphate equivalent to the barium sulphate obtained. 
or erythrosine.—Transfer to a 500 c. c. tall beaker that volume 
of the master solution which contains 1 gram of thedye. If the quan- 
tity taken is less than 100 c. c. add water to bring the solution to that 
volume. Add 50 c. c. of dilute nitric acid (1+ 49) to precipitate the 
color acid, stir, and let settle. Filter off the dye and wash once, 
collecting the washings with the filtrate. Over another 500 c. c. 
beaker dissolve the dye by passing through the filter paper as little 
dilute ammonium hydroxide solution (4+1) as is necessary and add 
water to bring the volume to 100 c. c. Neutralize the base and add 
nitric acid (1+ 49) to reprecipitate the color acid. Filter off the dye 
and wash once, collecting the filtrate and washings with those 
obtained after the first precipitation of color acid. (A 100 ¢. ¢. 
aliquot free of color acid may ‘is substituted, as directed in the first 
paragraph of this section.) Precipitate and determine the barium 
apne as directed in the first paragraph of this section. 
or light green S F yellowish.—Transfer to a 500-c. c. tall beaker 
that portion of the master solution which contains 2 grams of the 
dye. Add water, if necessary, to bring to a volume of 200 ec. ec. 
Heat to about 70° C. and filter. Wash the residue and paper with 
hot water. Dilute the combined filtrate and washings to about 250 
c. c., and add 5 c. c. of dilute hydrochloric acid (1+9). Complete 
73726°—26}——3 
