54 BULLETIN 448, U. S. DEPARTMENT OF AGRICULTURE. 
NATURAL COLORING SUBSTANCES. 
Relatively few good tests are known for the common natural 
colors. For properties useful in analysis, see especially the tables 
given in United States Department of Agriculture, Bureau of Chem- 
istry Circular No. 63. Some of the common properties considered 
most useful for the characterization of different colors are summarized 
below. 
By addition of concentrated hydrochloric acid, the yellow ether 
or alcohol solutions of carotin and xanthophyll show little change, 
becoming perhaps slightly paler; green chlorophyll solutions become 
yellower or browner; annatto in ether or alcohol solution remains 
orange, not changing perceptibly with acid. Turmeric solutions in 
ether or alcohol show a pure yellow color with more or less green 
fluorescence, and on addition of several volumes of concentrated hy- 
drochloric acid the color passes to orange red or carmine red. The 
orange or orange yellow solutions of logwood, also of the redwoods, 
barwood, sandalwood, camwood, and brazilwood, become deep red 
with excess of hydrochloric acid. The slightly colored neutral or 
faintly acid aqueous solutions of the flavone colors of fustic, Persian 
berries, quercitron, etc., become intensely yellow with from 2 to 4 
volumes of concentrated acid. Neutral or slightly acid solutions of 
cochineal, archil, saffron, and caramel show little change. 
The slightly acid solutions of the various coloring matters show the 
behavior described below, when treated with a little sodium hydro- 
oxid solution: Carotin and xanthophyll, little change; chlorophyll, 
" brown phase" reaction; alkanet, deep blue; turmeric, orange brown; 
the redwoods, violet red; logwood, violet to violet blue. The flavone 
colors become bright yellow; saffron remains yellow, showing little 
change. The red solutions of archil and the orange of cochineal 
become blue and violet, respectively. Caramel shows little change, 
becoming slightly deeper brown. The red fruit colors (in presence of 
air) become dull blue, green, or brown. 
By sodium hydrosulphite in acid solution, the yellow coloring 
matters are little affected. Logwood is almost decolorized, the color 
returning imperfectly. Archil is decolorized, the color returning when 
shaken with air. The reaction is more easily seen in alkaline solution. 
Cochineal shows no marked change. The anthocyanidins derived by 
hydrolysis from the red fruit colors are almost decolorized by hydro- 
sulphite. Caramel is rendered slightly paler. 
In the bromin test all coloring matters, except alkanet, are merely 
destroyed more or less completely by the halogen, hence they belong 
in general to Class E. The flavone colors tend to become darker with 
the first addition of bromin. Alkanet (best in alcoholic solution) 
corresponds to Class B. 
