FOOD-COLORING SUBSTANCES. 17 
Sec. 17. — The Sudans and similar dyes of this group may be further separated with 
gasoline and 90 per cent methyl alcohol. They may be separated from troublesome 
accompanying oily impurities, by shaking out the gasoline solution with 85 per cent 
phosphoric acid to which has been added from 10 to 20 per cent of concentrated sul- 
phuric acid, though some dye is likely to be destroyed in this treatment. 
Like the colors described in sections 15 and 16, these dyes are almost quantitatively 
removed from gasoline solution by 90 per cent phenol. The phenol may, of course, 
be dissolved in alkali and the color again taken up with ether or gasoline, effecting a 
separation from some impurities. 
Sec 18. — When Naphthol green B is present the salt solution should not be made 
strongly acid since small amounts of this dye decompose quickly in acid solution. 
When its presence is suspected, the neutral salt mixture may be first extracted with 
dichlorhydrin washed once with benzene to remove the dissolved solvent, made half 
normal with hydrochloric acid, and then shaken out with anilin. (It is best to add 
the solvent before the acid.) From the anilin solution the dyes may be fractionated 
by shaking out with 5 or 6 per cent salt solution which contains hydrochloric acid 
varying from fourth-normal to sixty-fourth-normal. 
No outline in the form of a key can be so useful as a table of solu- 
bilities. The solvents and the order hi which they are to be used 
obviously may be varied when the analyst has information regarding; 
the source and appearance of a sample. For example, in the case of 
the red color solution obtained from commercial cocktail cherries 
known to be ordinarily colored with Erythrosin, it would be better 
to make such solution acid and shake it out with ether first, the 
complete extraction of the dye indicating at once the absence of all 
excepting one group of colors. 
In the examination of dye solutions the analyst of some experience 
often will prefer (especially with colors extracted from acid, solu- 
tions by amyl alcohol) to wash the organic solvent extract with 
successive small portions of water instead of with hydrochloric acid 
or other aqueous solvent of definite concentration. In the case of 
an acid amyl alcohol extract much hydrochloric acid is taken up by 
the solvent along with the coloring matter. The acid is washed out 
rather slowly, and as a result of this gradually decreasing acidity of 
the washing coloring matters of different solubility will appear in 
maximum amount in different fractions, the order being apparent 
from the solubility tables. With binary mixtures usually some of 
each color is thus obtained pure enough for identification. 
The writer prefers, after fractionating the colors into the main 
groups as just described, to try the bromin test (page 47) . The be- 
havior with acids has already been seen in the course of the separation, 
and that with alkali can be quickly ascertained. Ordinarily these will 
indicate the fraction to contain but one coloring matter. This is 
then dyed out from a portion of the solution, and its shade and reac- 
tions on the fiber with reagents are compared with standards or with 
statements in the tables, in which, to facilitate comparison, the dyes 
have been arranged in the order of their solubility. Since the color 
61147°— Bull. 448—17 3 
