192 



METHODS OF ANALYSIS. 



3. Detection of Coal-Tar Colors by Extraction with Solvents.** 



In the Paris Municipal Laboratory & the following scheme of extraction of 

 coal-tar colors is used. 



The acid colors, sulphu-fuchsin, azo derivatives, and phthaleins are not pre- 

 cipitated 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. 



(a) To 50 cc of wine add ammonium hydroxid in slight excess; then add 15 

 cc of amyl-alcohol, shake, and allow to stand. 



(1) If the alcohol is colored red or violet, decant, wash, filter, evaporate to 

 dryness in presence of a piece of wool, and test the dyed wool with sulphuric 

 acid. 



(2) If the alcohol is not colored, separate, and add acetic acid. If the 

 alcohol becomes colored the presence of basic anilin color is indicated. 



(3) If the amyl-alcohol is uncolored, both before and after the addition of 

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



(b) Add an excess of calcined magnesia and then a 20 per cent solution 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. 



(c) Extract the solution with acetic ether 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 the following tables, the first of 

 which was prepared by Truchon and Martin-Claude,^ and the second by Tolin:m. 

 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. 



Extraction of fruit colors with amyl-alcohol. 



* See also the following circulars of the Bureau of Chemistry : No. 25, Coloring Mat- 

 ters for Foodstuffs and Methods for Their Detection, by W. G. Berry ; No. 35, Report on 

 Colors : The Solubility and Extraction of Colors and the Color Reactions of Dyed Fiber 

 and of Aqueous and Sulphuric-Acid Solutions, by H. M. Loomis. 



* Girard and Dupre", Analyse des matleres, etc., p. 167. 

 e J. pharm. chim., 1901, 18: 174. 



* Acidity of the juice. 



