18 BULLETIN 448, U. S. DEPARTMENT OE AGRICULTURE. 
changes produced in dilute dye solutions, by addition of acids and 
alkalies, are closely parallel to those shown by the same reagents on 
the dyed wool, a single table indicating the reactions on the fiber is 
sufficient in practice. 
Even when the tests have indicated that the fraction still contains 
a mixture of dyes, they will have shown, in most cases, the absence 
of many colors of the group, and will have indicated positively 
which colors are probably present. 
ABRIDGED PROCEDURE FOR PERMITTED DYES ONLY. 
A convenient abridgment of the fractionation procedure, suit- 
able when it seems probable that only permitted dyes are present, 
is the following : 1 
The solution or well divided solid matter containing the color is 
treated with one-half its volume of concentrated hydrochloric acid 
and is then extracted a few times with amyl alcohol. (For precau- 
tion concerning concentration in examining commercial food colors, 
see page 4.) The alcohol extracts are combined, then washed with 
four or five portions of fourth-normal hydrochloric acid, or until this 
solvent extracts very little color. These washings will contain any 
Indigo Carmine, Tartrazin, and Amaranth which were present in 
the alcohol solution. Indigo Carmine is removed from the amyl 
alcohol somewhat more readily than are the other two dyes. With 
ordinary concentrations little or no Ponceau will be removed. 
The amyl alcohol is then measured, if necessary, treated with an 
equal volume of petroleum ether or low-boiling-point gasoline, and 
again washed several times with fourth-normal hydrochloric acid to 
extract Ponceau 3 R and Naphthol yellow S. Or, without dilu- 
tion with gasoline, it may be washed with 5 per cent salt solution 
until these two dyes are taken out. After the Ponceau and Yellow 
have been removed the amyl alcohol, which contains an equal volume 
of gasoline, is washed a few times with water, thus extracting Orange 
I. After the removal of this dye the solution, although perhaps ap- 
pearing almost colorless, is shaken out with a very dilute caustic soda 
solution to remove Erythrosin. 
If considerable Orange I is present, some of it may contaminate 
the washings containing the Ponceau 3 R and Naphthol yellow S, 
especially when these have been separated by means of fourth- 
normal hydrochloric acid after addition of gasoline. 
The fourth-normal hydrochloric acid washings of the amyl alcohol 
may contain Indigo Carmine, Amaranth, and Tartrazin, their appear- 
ance in most cases indicating which of these dyes may be present. 
Instead of attempting to separate the dyes by fractionation the fourth- 
normal hydrochloric acid solution may be evaporated to dryness, 
i See also Price, U. S. Dept, Agr., Bur. Anim. Ind. Circ. 180. 
