FOOD-COLORING SUBSTANCES. 15 
however, that new dyes may also be formed by partial reduction in the case of polyazo 
or nitroazo derivatives. 
The halogenated fluorescein derivatives are much more resistant to bromin in 
acid solution than are most other colors. They tend, however, to add bromin unless 
fully substituted. Most of the azo dyes are much more readily destroyed by bromin 
in alkaline solution than is Naphthol yellow S. Mixtures are made fourth-normal or 
above with sodium carbonate and are treated with dilute bromin water very cautiously 
until the azo dye is just destroyed or until the solution has become a clear yellow. 
Hydrazin sulphate is now added quickly to destroy excess of bromin; the mixture 
is finally acidified, and the yellow purified by extraction with an immiscible solvent. 
This procedure is seldom so satisfactory as the regular extraction with ethyl acetate 
or amyl acetate, and is not applicable in the presence of Nos. 62, 64, 65, and 188, which 
form intensely blue substances by this treatment. 
Sec. 10. The amyl alcohol extract obtained by shaking out the original mixture 
after adding 5 or 6 per cent salt will contain practically all of any basic dyes present. 
Most of the acid dyes of low sulphur content are also almost completely extracted. 
The extract is measured, diluted with an equal volume of gasoline, then washed a 
few times with sixty-fourth-normal hydrochloric acid. The washings, if colored, are 
treated as directed in section 11. The extract is next shaken out with sixty-fourth- 
normal acetic acid, these washings being treated according to section 12. Eosins and 
(in general) coloring matters that are unsulphonated phenolic compounds are now 
removed by a few portions of sixty-fourth-normal sodium hydroxid solution, this 
fraction being treated according to section 13. The amyl alcohol gasoline mixture is 
finally washed once with very dilute acetic acid and, if still containing any signifi- 
cant amount of coloring matter, is evaporated to dryness on the steam bath, the 
residue being examined according to section 14. 
Sec 11. The washings of sixty-fourth-normal hydrochloric acid (sec. 10) are tested 
for basic dyes by making a small portion alkaline with sodium hydroxid, shaking 
with ether, then treating the ether solution, which is usually colorless, with dilute 
acetic acid. 1 If the latter becomes colored, indicating the presence of basic dyes, 
the alkaline test portion may be shaken out once or twice more to determine whether 
or not acid dyes are also present in this fraction. If these tests indicate the presence 
of both acid and basic colors, the acid colors must be removed by making the principal 
part of the sixty-fourth-normal hydrochloric acid extract alkaline (normal with 
sodium hydroxid) and extracting with ether. From the combined ether portions 
the basic dyes are removed by washing — first with sixty-fourth-normal acetic acid, 
finally with dilute hydrochloric acid. This treatment should be omitted if acid dyes 
are absent, since most basic colors are unstable in alkaline solutions, Auramin, espe- 
cially, suffering decomposition rapidly. The basic colors may be further fractionated 
from amyl alcohol with dilute hydrochloric acid, from ether with very dilute alkali, 
etc . The separation of basic colors from alkaline solutions by immiscible solvents is 
rather objectionable, since such colors (according to Kehrmann, Havas, and Grand- 
mougin 2 ) suffer rearrangement from ortho-quinoid to para-quinoid structure. This 
change is attended in compounds such as Crystal Violet, containing only fully alky- 
lated amino groups, by elimination of one of the alkyl groups. The original dye 
may not be obtained therefore, but, instead, the lower alkylated derivative. 
The alkaline solution, after removal of the basic dyes with ether, is made about 
normal with hydrochloric acid and is shaken out with amyl alcohol gasoline mixture. 
Any coloring matter extracted here probably will be a minor portion of a dye already 
obtained by the procedure described under section 8 , and its further fractionation will be 
carried out as stated in that paragraph; or the solution containing it may be combined 
i O. N. Witt, Z. Anal. Chem. 26 (1887), 100. Weingartner, Z. Anal. Chem. 27 (1888), 232. 
a Ber. Chem. Ges. 46 (1913), 2131; 47 (1914), 1881. 
