FOOD-COLORING SUBSTANCES. 49 
reactions take place, so that a more or less strong coloration is pro- 
duced on treatment with sodium carbonate without previous addi- 
tion of the naphthol. Crystal Scarlet (No. 64), Bordeaux B (No. 65), 
and Palatine Red (No. 62) give strong blue colorations; Naphthol 
Black (No. 88) and Amaranth (No. 107) a less intense blue color. 
Azorubin (No. 103) gives a purple changing to bluish red, but not 
very intense. Except for the first three dyes named, the colora- 
tions are considerably less intense than the original dyes, and the 
reaction much less trustworthy and valuable than the smooth, 
almost quantitative, reaction in acid solutions. When treated with 
bromin in solutions containing sodium carbonate (one-fourth nor- 
mal), Nos. 62, 64, and 65 are bleached, becoming intensely blue on 
addition of hydrazin sulphate. 
Class B. — Azin derivatives, 1 etc. — On treatment with bromin in 
neutral or acid solutions, the color is readily bleached, but is restored 
on adding hydrazin sulphate. Sodium carbonate and alpha- 
naphthol plus sodium carbonate produce no change other than that 
shown by the original dye solution on treatment with alkali. A few 
dyes of Classes A and AA when oxidized in neutral solutions tend to 
show a rather marked coloration on adding the hydrazin sulphate. 
However, with the typical members of Class B, the dye maybe bleached 
and restored a number of times by careful alternate addition of the two 
reagents, the bromin apparently forming a nearly colorless compound 
reconverted into the original dye on addition of the hydrazin sulphate. 
Class C. — Colors giving 'precipitates at dilutions as high as 0.01 per 
cent. — This class includes most of the basic dyes. 
Class D. — Colors showing marked changes in tint in neutral or very 
faintly acid solution on addition of bromin. 2 — The colorations are 
usually produced by a mere trace of the halogen and destroyed by 
excess, and the reactions are consequently not very dependable or 
valuable. With many of the dyes of this type containing alkylated 
amino groups the color change would seem to be due to elimination 
of alkyi radicals. In general with dyes of this group the coloring 
matter, while readily altered, is completely broken down by bromin 
only with difficulty. On addition of hydrazin sulphate no change 
takes place other than that due to removal of the excess of the col- 
ored halogen. 3 The coloration with alpha-naphthol and sodium 
carbonate is identical with that produced by sodium carbonate 
alone. With most of the yellow coloring matters of this group it is 
i Quinophthalon by treatment with bromin first forms the unstable colorless addition product con- 
taining two atoms of bromin in the molecule (Eibner and Lange, Liebig's Annalen der Chemie, 315 
(1901), 315), For action on azin dyes compare Vaubel, J. prakt. Chem., 54 (1896), 289. 
2 According to Heumann, Die Anilinfarben, vol. 1, p. 41, Malachite Green solution, on oxidation with 
lead peroxid and acetic acid, becomes violet, and then contains the salt of diaminotriphenylcarbinol. 
Compare further Vaubel, J. prakt. Chem., 50 (1894), 347. 
8 Cblorin water may be used if preferred. 
