b 
~~ 
; 
+e 
X 
PERMITTED COAL-TAR FOOD DYES 31 
to dryness. (Take care to prevent the access of reducing gases or 
vapors to the mixture.) Treat the residue with 5 c. c. of 7 per cent 
potassium permanganate and 5 c. c. of strong nitric acid and again 
evaporate to dryness. Add about 50 c. c. of water and 5c. c. of 
strong nitric acid to the residue. Then add 40 c. c. of a saturated 
solution of sulphur dioxide (p. 15), break up the lumps with a glass 
rod, and let stand, with occasional stirring, until the hydrated oxide 
of manganese is dissolved. Filter, wash the paper thoroughly with 
water, add an excess of 10 per cent silver nitrate solution to the com-. 
bined filtrate and washings, and boil until sulphur dioxide has been 
expelled and the silver iodide has flocculated. Collect the precipitate 
on a weighed Gooch crucible, wash with hot water, dry, and weigh. 
Calculate as percentage of free iodine and from this subtract the per- 
centage of iodine found as sodium iodide (p. 30). 
TOTAL HALOGENS 
For erythrosine.—Mix 0.5 to 1 gram of the dye with 4 grams of 
potassium carbonate and moisten to a paste with 50 per cent alcohol. 
Dry, cover with a layer of dry potassium carbonate, and ignite at a 
low red heat. Allow to cool, moisten with a few drops of water, and 
break up the charred mass thoroughly. Wash into a beaker and 
bring to a volume of about 200 c. c. with water, allow to digest for 
15 minutes, and filter. Wash the insoluble matter until the wash- 
ings no longer react with silver nitrate; then acidify the filtrate and 
washings with nitric acid, using an excess equivalent to 5c. c. of the 
strong acid, and precipitate the halogens with 10 per cent silver 
nitrate solution. Collect the precipitate on a weighed Gooch crucible, 
wash, dry, and weigh. Compare with the sum of the results ob- 
tained in the separate halogen determinations. 
SODIUM CARBONATE IN ERYTHROSINE 
APPARATUS 
Arrange a train of apparatus as shown in Figure 4. A glass tube 
(A), with an internal Menioter of about 15 mm. and filled as shown 
with solid glass beads, is inserted in a round-bottom 1000 c. c. flask 
(B). This flask is connected with a 600 ¢. c. flask (£), fitted with a 
perforated rubber stopper, through which pass the delivery tube of a 
short reflux condenser ((), the stem of a small dropping finned (D), 
and a tube (/’), leading to three 16-ounce bottles (4, H, and J). Gis 
prily filled with carbon-dioxide-free water (about 300 c. c.) and glass 
eads; H and I contain about 300 c. c. of 50 per cent sodium hydroxide 
solution and glass beads. 
A U-tube containing standard barium hydroxide solution may also 
be provided to show whether or not the apparatus has been freed 
from uncombined carbon dioxide and whether all the carbon dioxide 
in the sample has been taken up by the barium hydroxidein B. Ifa 
cloudiness develops in the U-tube at the end of the procedure, showing 
that the carbon dioxide has not been completely taken up, repeat the 
-— analysis, using a smaller sample of dye. When connection is made 
with the air pump, provide the rubber tubing used with two screw 
clamps or some other device that will permit the rate of the flow of air 
drawn through to be readily and accurately adjusted, 
