77 



to quarter strength or less, and filter; to the filtrate add a 

 small quantity of hydrochloric acid. 



(c) Boil the woolen strips for five or ten minutes in the 

 solution made in (b), remove them, wash them thoroughly 

 in warm water, and note their final color. If coal tar dyes 

 are present, the strips will become vividly colored. 



(d) Repeat the test, this time using home catchup, jelly, 

 or wine. Is there any difference in the color acquired in 

 (c) and (d} by cloth strips ? 



Vegetable and fruit juices usually stain wool a faint and 

 dull color, and the pupil must not confound this natural 

 coloration with the vivid hues of the coal tar dyes. 



EXPERIMENT 72. TO DETECT ARTIFICIAL COLORING 

 MATTER IN FOODS 



(a) Boil a piece of white woolen cloth in a one-tenth 

 solution of sodium hydroxide (NaOH), and then wash it 

 thoroughly in water. 



(b) Dilute 10 c.c. of the suspected food material, such as 

 ice cream, catchup, or the sirup of canned fruits, etc., with 

 50 c.c. of water. To this, add 5 c.c. of a 10 per cent solu- 

 tion of potassium bisulphate, and boil the mixture. 



(c) Into the liquid formed in (b) place the woolen cloth, 

 and allow it to boil about ten minutes. 



Remove the cloth, wash it thoroughly in boiling water, 

 and dry it between filter paper. If the white cloth 

 acquires a bright red color, coal tar dye is present in 

 the food material being tested. 



If the white woolen cloth does not become bright red, 

 the pleasing color of the food is due to pure fruit, and not 

 to coloring matter from coal tar dyes. 



