FOOD-COLORING SUBSTANCES. 55 



Ferric chlorid gives no marked change with annatto, turmeric, 

 or saffron, these perhaps, appearing somewhat browner. With the 

 flavone colors, colorations varying from dark olive green to black 

 are produced. With the redwoods and logwood, very dark shades of 

 violet, brown, or black are obtained. Cochineal becomes somewhat 

 darker. Caramel is not affected. The solutions must be practically 

 neutral. 



By addition of alum solution the yellow color of logwood is changed 

 to rose red (rather slowly). The redwoods are affected similarly. 

 The pale yellow solutions of the flavones become more strongly 

 yellow, that of fustic developing a green fluorescence. Saffron and 

 turmeric show Httle change. 



Uranium acetate in neutral or nearly neutral solutions gives 

 orange colorations with the flavones. Turmeric becomes somewhat 

 browner; saffron is not affected; cochineal becomes green; alkanet, 

 yellowish green to bluish green; logwood, violet, quickly fading. 



The coloration with concentrated sulphuric acid dropped on the 

 dry coloring matter is for carotin and xanthophyll, blue, usually 

 obtained with difficulty. Annatto and saffron also give blue colors; 

 turmeric, a red; the flavone colors, yellow or orange colorations; 

 alkanet and archil give violet blue; logwood, red, changing to yellow. 



The "brown phase" reaction^ m&j be useful for the characteriza- 

 tion of chlorophyll, when this has not been previously treated with 

 alkahes. The gi-een ether or petroleum ether solution of the coloring 

 matter, when treated with a little methyl alcohol solution of potas- 

 sium hydroxid, becomes brown, returning to green in a few moments. 



The characteristic reaction of curcumin (turmeric) with boric 

 acid may be conveniently carried out as follows: The aqueous or 

 dilute alcohohc solution of the color is treated with hydrochloric acid 

 until the shade just bcgms to appear slightly orange. The mixture 

 is then divided into two parts and some boric acid powder or crystals 

 added to one part. A marked reddening quickly will be apparent, best 

 seen by comparison with the portion to which the boric acid has not 

 been added. ^ 



I MoUsch, Ber. bot. Ges. 14 (1896), 16. Willstaetter and StoU, Untersuchungen ueber CUorophyU. 

 Berlin, 1913, p. 144. 



« The properties of pure preparations of the various natural coloring matters, as described by the nu- 

 merous investigators who have isolated and studied them, are described for the most part in 11. Rupo's 

 Oiemie der Naturlichen Farhnlnffe, Braunschweig, 1900 and 1909. Properties of the chlorophylls and 

 fartinoids are given by Willstaetter and StoU, Unler.iuchuTigen ucbcr Chlorophyll , Berlin, 191.3; those of the 

 coloring matters of the cornflower, rose, pi^argona flower, larkspur, cranberry, whortleberry, and purple 

 grai»e, are de;yribcd by Willstaetter and coworkers. Sitzb. kgl. Pruess. Akad. 12 (1914), 402, Liebigs 

 Ann. d. Chem. 408 (1915) 1. 



