PERMITTED COAL-TAR FOOD DYES 19 
hygroscopic that they may be weighed in the container on an even- 
weight basis.) Heat at a low temperature until most of the dye 
has been volatilized. Moisten the residue with concentrated sul- 
phuric acid and complete the procedure as directed in the first 
paragraph of this section, beginning with “‘and heat over a ring 
burner.” Inasmuch as yellow A B and yellow O 5 contain no 
metallic element, the presence of any sulphated ash is due to im- 
purities. This suiphated ash, although not subject to calculation 
in terms of sodium or other base of the color, is reserved for the 
determination of heavy metals. 
HEAVY METALS 
For ponceau 3R, amaranth, erythrosine, orange I, naphthol yellow S, 
tartrazine, guinea green B, light green S F yellowish, and indigotine.— 
Moisten with 5 c. c. of strong hydrochloric acid the sulphated ash 
obtained in the sulphated-ash determination and evaporate to dry- 
ness on a steam bath. Warm the residue with 20 c. c. of hydro- 
chloric acid (1+19) until all soluble material is dissolved. Transfer 
to a 100 ec. c. volumetric flask, dilute to the mark, mix, and filter 
through a dry paper. Reserve two 40 c. ec. portions for the iron, 
aluminium, calcium, and magnesium determinations. Pour the rest 
of the filtrate into a test tube and pass in a washed stream of hydrogen 
sulphide for 30 minutes. No turbidity other than that due to pre- 
cipitated sulphur should appear. If a colored precipitate is formed, 
filter and test it for copper and tin. Make the solution shghtly 
alkaline with ammonium hydroxide (1+1). A white precipitate 
indicates the presence of zinc, which is not tolerated; a marked 
coloration indicates that the quantity of iron should be determined. 
For yellow A B and yellow O B.—The color of the sulphated ash, 
obtained as directed above, shows whether the ash is mainly iron 
oxide or silica. In either case fuse it with 1 gram of potassium car- 
bonate (reagent quality) until the silicates have been decomposed. 
Moisten the residue with 2 or 3 c. ¢. of strong hydrochloric acid, 
evaporate to dryness on a steam bath, and treat as directed in the 
first paragraph of this section. If only a trace of iron oxide or 
silica is present in the original ash, the fusion with potassium car- 
bonate may be omitted. 
IRON, ALUMINIUM, CALCIUM, AND MAGNESIUM 
For ponceau 3R, amaranth, erythrosine, orange I, naphthol yellow 
S, tartrazine, yellow A B, yellow O B, quinea green B, light green S F 
yellowish, and endigotine.—To one of the two portions reserved as 
directed above add 5 grams of ammonium chloride and neutralize 
with ammonium hydroxide (1+1), boilmg to drive off any excess. 
If the precipitate is very slight, it may be neglected; otherwise, filter 
through a quantitative paper, wash (reserving the filtrates and wash- 
ings), and ignite paper and precipitate in a weighed crucible. Weigh 
the mixture of iron oxide (Fe,O,) and aluminium oxide (Al1,O,). 
Place the mixed oxides in a 500 c. c. Erlenmeyer flask and dissolve 
in aqua regia, boiling to drive off chlorine. Add water to bring the 
volume to about 75 ¢. c. and add ammonium hydroxide to incipient 
precipitation. Dissolve the precipitate with as little hydrochloric 
acid as possible and cool. ‘Titrate the ferric iron present with 0.1 
