COAL-TAR FOOD DYES 
SUBSIDIARY DYES 
For brilliant blue FCF. — Proceed as directed for light green SF 
yellowish (2, p. 81), except that after removal of the dye from the 
alcohol make the comparison with a standard solution of brilliant 
blue FCF and report as percentage of subsidiary dye. 
LEAD 
(Applicable to all perm." 
Reagents 
Ammonium acetate. — Dissolve 200 gm. of pure ammonium acetate 
NH 4 (C 2 H 3 (Vi in water and dilute to 500 c. c. 
Dilute ammonium acetate solution. — Dilute 50 c. c. of the strong 
ammonium acetate to 500 c. c. 
Procedure 
* Place 10 gm. of dye (15 gm. if necessary in a tall 1,000 c. c. pyrex 
beaker, add 20 c. c. of concentrated nitric acid, and let boil. Then 
add 30 to 35 c. c. of concentrated sulphuric acid and continue the 
heating. Add small quantities of concentrated nitric acid at intervals 
until the organic matter is destroyed and the solution remains yellow 
or colorless when evaporated until sulphur trioxide fumes are freely 
evolved. Let cool and transfer the contents to a platinum dish. 
Continue the heating until the production of acid fumes decreases. 
If any carbon remains, moisten with a few drops of concentrated 
sulphuric acid and continue the heating. Finally, heat over the 
blast lamp or in a muffle furnace until fusion takes place, with the 
production of a clear liquid, free from bubbles. 
Cool the dish and add about 5 c. c. of concentrated hydrochloric 
acid and evaporate until acid fumes can no longer be detected. Then 
add 2.5 c. c. of concentrated hydrochloric acid and about 20 c. c. of 
distilled water, and warm on the steam bath until all soluble matter 
goes into solution. Transfer to a 250 c. c. volumetric flask, dilute to 
the mark, and filter. 
At tins point a qualitative test for heavy metals should be made. 
For this purpose, place an aliquot part of the filtrate representing 
1 gm. of ch~e in a test tube and saturate with washed hydrogen sul- 
phide gas. Then place the test tube in a beaker containing boiling 
water and let it remain until the excess hydrogen sulphide has escaped. 
The presence of heavy metals is indicated if a dark precipitate settles 
out on standing. Place a 5 gm. aliquot portion of the filtrate in a 
tall 300 c. c. pyrex beaker, add about 3 c. c. of concentrated sulphuric 
acid, and evaporate until copious S0 3 fumes are evolved. Take up 
in 100 to 150 c. c. of water and add an equal volume of 95 per cent 
alcohol. Let stand overnight, filter through a small double filter 
(C. S. & 5. 590), 2 and wash thoroughly with 50 per cent alcohol, using 
a wash bottle for the purpose. 
Place the filter paper in a small beaker, add 20 c. c. of the strong 
ammonium acetate, and heat on the steam bath, breaking up the 
paper with a glass rod. Filter through a quantitative paper 
(C. S. & S. 590) 2 into a 50 c. c. volumetric flask and wash the paper 
and contents with dilute ammonium acetate until the filtrate reaches 
the mark. 
* If desired, suitable fritted glass crucibles may be used for these nitrations . 
