FOOD-COLORING SUBSTANCES. 13 
The acid yellows (No. 8 and No. 9) although chiefly extracted by amyl alcohol from 
the acid solution (sec. 2) always yield a large fraction in this group. When the colora- 
tion of the extracted acid salt mixture is entirely due to such products it will be orange 
red, becoming yellow on neutralization, and also will show the characteristic reactions 
of the acid yellows with nitrous acid, etc. 
Sec. 5. The dichlorhydrin solution is diluted with three or four times its volume 
of carbon tetrachlorid and the color removed with a few small portions of water. 
The combined washings should be shaken out once with carbon tetrachlorid to get 
rid of dissolved dichlorhydrin. The aqueous solution may contain the higher sul- 
phonated triphenylmethane colors or perhaps sulphonated indulin. These dyes, 
like Acid Magenta, are accompanied by large amounts of subsidiary products, and 
their solubilities can not be established with any definiteness. For their further 
differentiation compare their properties as shown in the tables. 
Sec. 6. The amyl alcohol extract of the strongly acid salt solution, if colored, is 
washed four or five times with fourth-normal hydrochloric acid, the washings being 
kept separately. No. 108 and No. 692 predominate in the first washings, while the 
acidity is still high, because of hydrochloric acid dissolved in the amyl alcohol. No. 
106, No. 107, and No. 94 come out in large proportion when the acidity of the lower 
layer, after the shaking, is below seven-tenths normal (usually about the third wash- 
ing). Obviously a stronger acid than fourth-normal may be used at first, but it is 
usually better in practice to wash with this concentration and refractionate if neces- 
sary. The dyes that may be present in the acid amyl alcohol extract show a gradual 
transition in their distribution ratios relative to amyl alcohol (and other like solvents) 
and hydrochloric acid of varying concentration. Consequently the acid normalities 
to be chosen in working with an unknown mixture must be selected somewhat accord- 
ing to probabilities. 
Comparison of the appearance of the different washings usually will show whether 
more than one color is present which is extracted by fourth-normal hydrochloric acid 
in considerable proportion. The amyl alcohol is reserved for the treatment described 
in section 7 or 8. No. 108 may be separated from Nos. 106, 107, and 94 by fractiona- 
tion between two-normal hydrochloric acid and amyl alcohol. Nos. 692 and 8 can be 
separated from Nos. 106, 107, and 94 similarly with eight-normal sulphuric acid and 
a mixture of equal volumes of amyl alcohol and gasoline; although, since the acid is 
somewhat difficult to remove afterwards, the procedure is better adapted for sepa- 
rating the last-named dyes in pure condition than Nos. 692 and 8. For Nos. 106, 107, 
and 94, the amyl alcohol gasoline solution is washed with a little water to take out the 
dye. This solution is treated with one-half its volume or more of concentrated hydro- 
chloric acid and is reextracted with amyl alcohol. This latter solution may now be 
washed with a few portions of hydrochloric acid of from four to six normal strength to 
remove sulphuric acid. The dye is finally removed with a little water and the color 
obtained in pure condition (for the cyanid reaction, for example) by evaporation to dry- 
ness on the steam bath. The dyes in the sulphuric acid solution are best separated by 
anilin (compare p. 23); but the final removal of this solvent is tedious. No. 94 must 
be separated from No. 106 and No. 107 by anilin and fourth-normal hydrochloric 
acid in 5 or 6 per cent salt solution. After the fractionation the dissolved anilin in 
the solutions must be carefully removed by several extractions with carbon tetra- 
chlorid or other convenient solvent from the faintly alkaline solution. 
Commercial No. 692 and No. 8 are made by direct sulphonation of coloring matters 
and are rather indefinite in composition. It will often be more convenient to divide 
the solutions of the colors of this group and to destroy different dyes in the various 
portions. By cautious treatment with "Blankite" (Na 2 S 2 4 ) in acid solution, sub- 
sequently shaking with air to restore the blue, No. 692 may be separated from the azo 
colors. 
