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PERMITTED COAL-TAR FOOD DYES 29, 
For ponceau 3R.—Proceed as directed in the first paragraphs of this 
section, but use a mixture of equai volumes of amyl alcohol and gaso- 
line (specific gravity 0.65) in place of the amyl alcohol and run the 
blank with 1 mg. of ponceau 3R. Calculate the result as percentage 
of sodium trimethylbenzene-azo-G-naphtholsulphonate, using the 
factor 0.009807. 
For indigotine.—Proceed as directed in the first paragraphs of this 
section, but use 0.25c. c. of acid instead of 1 c. c., wash with sixteenth 
normal instead of 0.25 N acid, and run the blank with 1 mg. of indi- 
gotine. Calculate the result as percentage of sodium indigo mono- 
sulphonate. One cubic centimeter of 0.1 N titanium trichloride 
solution is equivalent to 0.01821 gram of sodium indigo mono- 
sulphonate. 
For light green S F yellouish.—To a solution of 125 grams of sodium 
chloride in 400 ec. c. of water add 12 c. ec. of glacial acetic acid and a 
solution containing 13.6 grams of sodium acetate (NaC,H;0..3H,O) 
and dilute to 500 c. c. Tothat volume of the master solution which 
contains 0.1 gram of the dyeadd water, if necessary, to bring toavolume 
of 10 c.c. Dilute with 40c. c. of thesalt-acetate solution and extract 
successively in three separatory funnels, each containing 100 e. ec. 
of amyl alcohol. Wash the extracts with three 100 c. c. portions of 
the salt-acetate solution, passing each wash portion successively 
through the three funnels in the order followed in making the original 
extractions. Remove the dye from the alcohol as directed in the 
first paragraph of this section and determine colorimetrically by 
comparison with a standard guinea green B solution of approxi- 
mately the same strength. Report as percentage of guinea green B. 
BOILING POINT OF ¥-CUMIDINE FROM PONCEAU 3R 
REDUCTION AND EXTRACTION 
Dissolve 60 grams of the dye in a 600 to 700 c. c. beaker with about 
450 c. ce. of boiling water and add it very slowly to a warm (60° to 
80° C.) solution of 100 grams of stannous chloride in 100 ec. c. of 
strong hydrochloric acid in a tali 1200 c¢. c. beaker. Add 10 to 
20 c. c. of the dye solution at a time, waiting after each addition 
until the mixture is pale brown. Otherwise the dye will be precipi- 
tated, in which case it can be reduced only with difficulty. As 
reduction proceeds and the solution becomes more dilute heat to 
boiling, taking care that the mixture does not boil over after each 
addition of dye, as some heat is generated by the reaction. After 
all fhe dye has been added and reduced, let the mixture cool and make 
it alkaline by adding about 75 grams of sodium hydroxide dissolved 
in 150 to 200 c. c. of water. 
Cool the alkaline mixture and shake it with three 200 c. c. portions 
of ether. Combine the ether extracts of y-cumidine thus obtained 
and wash with water until the alkali and salts are removed. Evapo- 
rate the solvent on the steam bath, but avoid such prolonged heating 
as may tend tovolatilize the base. Transfer the residue of Y-cumidine 
to a small side-neck flask and distil it, carefully avoiding overheat- 
ing. Observe the range within which the substance volatilizes, 
