1-i BULLETIN 448, U. S. DEPARTMENT OF AGRICULTURE. 
By reduction in ammoniacal solution, avoiding excess of "BlanMte," No. 106 and 
No. 107 may be destroyed, while No. 8 is merely converted into the hydrazo com- 
pound and may be restored by shaking with air. No. 692 is destroyed by warming 
in acid solution containing a little urea and a drop of sodium nitrite solution, while 
Nos. 106, 107, and 108 are scarcely attacked. The cyanid reaction is best suited for 
the examination of mixtures of No. 106 and No. 107. 
The dyes of this group, because of their ready solubility in water and fruit juices, 
are well adapted and largely employed for food coloring. Hence the application of 
the data given in the solubility table, etc., has been indicated rather more fully here 
than for the other classes. 
Sec. 7. The amyl alcohol extract after being washed with fourth-normal hydro- 
chloric acid may be similarly washed with sixteenth-normal hydrochloric acid; 
although unless No. 14 or No. 188 appear to be present this step usually will be 
omitted. 
Sec. 8. The amyl alcohol is now measured, diluted with an equal volume of low- 
boiling-point gasoline, and washed first with fourth-normal hydrochloric acid two or 
three times, then similarly with sixteenth-normal hydrochloric acid, with sixty- 
fourth-normal hydrochloric acid, with sixty-fourth-normal acetic acid, and finally 
with sixty-fourth-normal sodium hydroxid. The dyes separated here include a 
large number of individuals and the treatment most desirable for any given mixture 
can best be judged after reference to the tables, pages 24 to 29. Obviously, the 
normalities stated are chosen somewhat arbitrarily, any two dyes contiguous in the 
table usually differing little from each other in solubility. When the appearance, etc., 
of the different fractions indicate the presence of more than one dye, the coloring mat- 
ters must be obtained in pure condition by refractionation. Although the acid amyl al- 
cohol extract, after dilution with gasoline, appears to yield all its color to the acid wash- 
ings, it must nevertheless be shaken with the alkaline solution before being discarded, 
since a number of the weakly acid coloring matters (most of which, it is true, do not 
properly come in this group) are nearly colorless when dissolved in the neutral or acid 
organic solvent. 
Naphthol yellow S. which predominates in the first strongly acid washings, is also 
nearly colorless in acid solutions, and a portion from these solutions must always be 
tested for this dye by making double normal with hydrochloric acid and shaking with 
washed ethyl acetate. If the separated solvent is found by treatment with alkali to 
have taken up a yellow dye, the remainder of the fractions containing it are treated in the 
same way with the acetate. Although the washings of low acidity may contain some 
coloring matters, the major portion of such dyes will be in the amyl alcohol extract 
of the neutral salt solution. It is best, therefore, to set aside the sixty-fourth-normal 
acetic acid and the sixty-fourth-normal sodium hydroxid washings until after the 
examination of the neutral salt amyl alcohol extract has been made; or these solutions 
may be mixed with the corresponding ones obtained by the processes outlined in 
sections 11 and 12 and may be worked up with them. Or, finally, the amyl alcohol 
gasoline mixture, after washing with sixty-fourth-normal hydrochloric acid, may be 
reserved and combined with the similar mixture described in section 10. 
Sec. 9. For the separation by chemical means of closely similar dyes of these 
groups some of the more useful general methods may be indicated here. 
The reaction with cyanid (page 52) may be used for the separation of R-salt deriva- 
tives (Nos. 55, 56, 65, 15) from mixtures with isomers. 
Methods based on reduction and subsequent oxidation are applicable for the destruc- 
tion of azo and nitro colors in presence of most other classes of colors, as indicated in 
the tables of Weingartner and of Rota. 
By cautious reduction in sodium carbonate or ammoniacal solution oxyazo dyes 
tend to be attacked more rapidly than aminoazo dyes. It must be remembered. 
