PERMITTED COAL-TAR FOOD DYES oT 
must be fixed by titration against a freshly made solution of indigotine 
of known purity, the same conditions of concentration and acidity 
being maintained. Calculate as percentage of dye. 
MATTER INSOLUBLE IN CARBON TETRACHLORIDE 
a 
For yellow A B and yellow O B.—In a 100 c. c. beaker mix 5 grams 
of the dye with 50 c. c. of carbon tetrachloride, stir, and heat to 
boiling. With carbon tetrachloride wash to constant weight a 
Gooch crucible prepared as directed on page 14, except that ignition 
is omitted. Filter the hot dye solution through the crucible, trans- 
ferring to it the residue in the beaker, and wash with five 106. c. 
portions of carbon tetrachloride. Dry at 100° to 105° C. and 
weigh. Report the percentage increase in weight as matter insoluble 
in carbon tetrachloride. 
: WATER EXTRACTIVES 
For yellow A B and yellow O B.—To determine the neutral extrac- 
tives, proceed as follows: Place 5 grams of the well-powdered dye in 
a 500 c. c. Erlenmeyer flask or wide-mouth bottle, add 200 c. c. of 
water, and stopper. Mix by shaking vigorously several times dur- 
ing 2 hours. Filter the mixture, reserving the dye, and evaporate 
100 c. c. of the filtrate in a weighed platinum dish on a steam bath. 
Dry in an oven at 100° to 105° C., cool in a desiccator, and weigh. 
Report the percentage increase in weight as neutral water extrac- 
tives. Test small portions of the remainder of the filtrate for chlo- 
rides, sulphates, and nitrates. If more than traces are present, 
make the proper analyses on aliquot portions of the filtrate. 
To determine the acid extractives, proceed as follows: In 100 ¢. ¢. 
of benzene dissolve the dye reserved from the neutral extractive 
determination. Extract in a separatory funnel with two successive 
25 c. c. portions of hydrochloric acid (1+9). Combine the extracts 
and wash once with 25 c. c. of benzene. Draw off the acid extract 
into a weighed platinum dish. Discard the benzene and wash the 
funnel with 10 c. c. of hydrochloric acid (1+9), adding this washing 
to the extract in the dish. Evaporate to dryness on the steam bath, 
cool in a desiccator containing calcium chloride, and weigh. Report 
the percentage increase in weight as acid water extractives. 
MELTING POINT 
APPARATUS 
Set up the apparatus (fig. 3), consisting of a tube about 15 cm. 
long and 3.5 em. in internal diameter, with a bulb of 5 cm. internal 
diameter. Fill the tube with glycerin or sulphuric acid to about 
the height indicated. Fit the tube with a cork stopper carrying a 
ay tube (A), 5 mm. in diameter, which reaches nearly to the 
ottom of the bath, an ordinary test tube (B), in which a stand- 
ardized thermometer (C) is suspended by means of a rubber stopper 
in such a manner that the mercury column is wholly within the 
tube and the mercury bulb equidistant from its walls, a long-stemmed 
thermometer (D), supported so as to reach a short distance below 
the tube B, and an outlet tube (£) to permit the escape of air and 
vapor. 
