XI] COLORING MATTERS IN FOODS 165 



Hydrochloric acid. — Add concentrated acid (sp. gr. 1.20) to the solution, first 

 1 or 2 drops, then a large excess, equal to 3-4 times the volume of the solution. 



Sodium hydroxid {-potassium hydroxid). — Make the solution slightly alkaline by 

 adding a drop of the 10% sodium hydroxid solution. A 10% solution of potassium 

 hydroxid in methyl alcohol must be used for the "brown phase reaction" for chloro- 

 phyll, described in 23, and may also be employed for the other tests. 



Sodium hyposulphite. — Add the sodium hyposulphite solution drop by drop. 



Ferric chlorid. — Add a small amount of the 0.5% ferric chlorid solution to the 

 solution to be tested. The reagent must be added very carefully, a small drop at a 

 time, as the colorations are not obtained in all ca.ses when an excess is used. 



Alu7n. — Add to the test solution one fifth its volume of the 10% potassium or 

 ammonium alum solution. 



Uranium acetate. — Add the 5% uranium acetate solution drop by drop to the solu- 

 tion to be tested. 



Concentrated sulphuric acid on the dry color. — Evaporate a small amount of the 

 solution or of the coloring matter in a porcelain dish. Cool thoroughly and treat 

 the dry residue with 1 or 2 drops of cold, concentrated sulphuric acid. The color- 

 ations are in some cases extremely fugitive and may be observed only the instant 

 the acid wets the residue. 



The properties of pure preparations of the various natural coloring matters are 

 described, for the most part, by Rupe*^. Properties of the Chlorophylls and 

 Carotinoids are given by Willstiitter and StolP^. Those of the coloring matters of 

 the Corn Flower, Rose, Pelargona Flower, Larkspur, Cranberry, Whortleberry and 

 Purple Grape are described by Willstattcr^". 



