26 FRUITS AND FRUIT PRODUCTS. 



If the wool is well dyed most of these colors may be obtained on the 

 fabric. 



This gives only the reactions of a few of the more common colors. 

 In order to carry the work farther the more complete works referred 

 to will have to be used. 



DETECTION OF COAL-TAR COLORS BY EXTRACTION WITH SOLVENTS. 



In the Paris municipal laboratory a the following scheme of extraction 

 of coal-tar color is used: 



The acid colors, sulpho-fuchsin, azo derivatives, and phthaleins are 

 not precipitated by tannin and are insoluble or only slightly soluble in 

 acetic ether or amyl alcohol. 



The basic colors (fuchsin, safranin, etc.) are precipitated by tannin 

 and readily soluble in acetic ether or amyl alcohol. 



I. To 50 cc of wine add ammonium hydroxid in slightest excess; 

 then add 15 cc of amyl alcohol, shake, and allow to stand. 



1. If the alcohol be colored red or violet, decant, wash, filter, evap- 

 orate to dryness in presence of a piece of wool, and test the dyed wool 

 with sulphuric acid. 



2. If the alcohol be not colored, separate, and add acetic acid. If 

 the alcohol becomes colored the presence of basic aniline color is indi- 

 cated. 



3. If the amyl alcohol is uncolored, both before and after the addi- 

 tion of acetic acid, no basic coal-tar color is present. 



II. Add an excess of calcined magnesia and then a 20 per cent solu- 

 tion of mercuric acetate and bring to a boil. A coloration before or 

 after addition of acetic acid indicates the presence of coal-tar dyes, 

 particularly acid dyes. 



III. Extract with acetic ether the solution made alkaline by barium 

 hydroxid. This dissolves basic colors. 



In any case the colors must be fixed on wool, as many of the fruit 

 colors are extracted and will give reactions with sulphuric acid, which 

 may be mistaken for coal-tar colors. 



The extraction of fruit colors is shown in Table 1, prepared by Tru- 

 chon and Martin-Claude, b and Table 2, prepared by the writers. The 

 fresh fruit juice was very slightly acidified by hydrochloric acid 

 before extraction. In no case in the dyeing test was there any danger 

 of mistaking the vegetable color for one of coal-tar origin where the 

 double dyeing method was used. 



a Girard and Dupre, Analyse des Matieres Alimentaires, etc., p. 167. 

 b Journ. pharm. chim., 1901, 13, 174. 



