54 BULLETIN 448, V. S. DEPARTMENT OF AGEICULTUEE. 



NATURAL COLORING SUBSTANCES. 



Relatively few good tests are known for the common natural 

 colors. For properties useful in analysis, see especially tlie tables 

 given in United States Department of Agricultm-e, 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 sHghtly 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 yeUow 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 shghtly acid solutions of 

 cochineal, archil, saffron, and caramel show httle change. 



The shghtly 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 fiavone 

 colors become bright yellow; saffron remains yellow, showing httle 

 change. The red solutions of archil and the orange of cochineal 

 become blue and violet, respectively. Caramel shows little change, 

 becoming shghtly 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 httle 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 anthocyanidms 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. 



