168 METHODS OF ANALYSIS [Chap. 



Special Tests for Natural Coloring Matters. 



23 chlorophyll. 



The "brown phase reaction"-' may be useful for the characterization of Chloro- 

 phyll, when this has not been previously treated with alkalies. Treat the green 

 ether or petroleum ether solution of the coloring matter with a small amount of 

 10% solution of potassium hydroxid in methyl alcohol. The color becomes brown, 

 returning to green in a few minutes. 



annatto. 



24 Leach Test"-. 



Pour on a moistened filter an alkaline solution of the color obtiined by shaking out 

 the oil or melted and filtered fat with warm, dilute sodium hydroxid solution. If 

 Annatto is present, the filter paper will absorb the color so that, when washed with 

 a gentle stream of water, it will remain dyed a straw color. Dry the filter and add a 

 drop of stannous chlorid solution. If the color turns pink the presence of Annatto 

 is confirmed. 



25 turmeric. 



Carry out the highly characteristic reaction of Curcumine (Turmeric) with boric 

 acid as follows: Treat the aqueous or dilute alcoholic solution of the color with 

 hydrochloric acid until the shade just begins to appear slightly orange. Divide 

 the mixture into 2 parts and add some boric acid powder or crystals to 1 portion. 

 A marked reddening will be quickly apparent, best seen by comparison with the 

 portion to which the boric acid has not been added. The test may also be made by 

 dipping a piece of filter paper in the alcoholic solution of the coloring matter, drying 

 at 100°C., then moistening with a weak solution of boric acid to which a few drops 

 of hydrochloric acid have been added. On drying again a cherry-red color will be 

 developed. 



26 COCHINEAL. 



When the presence of Cochineal is suspected, acidify the mixture with one third 

 its volume of concentrated hydrochloric acid and shake with amyl alcohol. Wash 

 the amyl alcohol solution of the coloring matter 2-4: times with equal volumes of 

 water to remove hydrochloric acid, etc. Dilute the amyl alcohol with 1-2 volumes of 

 gasoline and shake with a few small portions of water to remove the color. Sepa- 

 rate the solution into 2 portions. To the first add, drop by drop, 5% uranium ace- 

 tate solution, shaking thoroughly after each addition. In the presence of cochineal 

 a characteristic emerald-green color is produced-^ The green coloration with 

 uranium salts is not developed in the presence of much free acid. Therefore add a 

 little sodium acetate before making this test or a correspondingly large amount of 

 uranium acetate must be added. To the second portion add a drop or so of ammon- 

 ium hydroxid, and, in the presence of Cochineal, a violet coloration results. This, 

 however, is not so sensitive to small amounts as the first test and many fruit colors 

 give tests hardly to be distinguished. 



As cochineal lakes very often contain tin, further examination for this metal 

 should always be made when water-insoluble cochineal compounds appear to be 

 present. 



