18 BULLETIN" 448, U. S, DEtARTMEXT OF AGRICULTURE. 



changes produced in dilute dye solutions, by addition of acids and 

 alkalies, are closely parallel to those shown by the same reagents on 

 the dyed wool, a single table indicating the reactions on the fiber is 

 sufficient in practice. 



Even when the tests have indicated that the fraction still contains 

 a mixture of dyes, they will have shown, in most cases, the absence 

 dl many colors of the group, and will have indicated positively 

 which colors are probably present. "" 



ABRroGED PROCEDURE FOR PERMITTED DYES ONLY. 



A convenient abridgment of the fractionation procedure, suit- 

 able when it seems probable that only permitted dyes are present, 

 is the following : ^ 



The solution or well divided solid matter containing the color is 

 treated with one-half its volume of concentrated hydrochloric acid 

 and is then extracted a few times with amyl alcohol. (For precau- 

 tion concerning concentration in examining commercial food colors, 

 see page 4.) The alcohol extracts are combined, then washed with 

 iour or five portions of fourth-normal hydrochloric acid, or until this 

 solvent extracts very little color. These washings will contain any 

 Indigo Carmine, Tartrazin, and Amaranth which were present in 

 the alcohol solution. Indigo Carmine is removed from the amyl 

 alcohol somewhat more readily than are the other two dyes. With 

 ordinary concentrations little or no Ponceau will be removed. 



The amyl alcohol is then measured, if necessary, treated with an 

 equal volume of petroleum ether or low-boiling-point gasoline, and 

 again washed several times with fourth-normal hydrochloric acid to 

 extract Ponceau 3 P and Naphthol yellow S. Or, without dilu- 

 tion with gasoline, it may be washed with 5 per cent salt solution 

 until these two dyes are taken out. After the Ponceau and Yellow 

 have been removed the amyl alcohol, which contams an equal volume 

 of gasoline, is washed a few times with water, thus extracting Orange 

 I. After the removal of this dye the solution, although perhaps ap- 

 pearing almost colorless, is shaken out with a very dilute caustic soda 

 .solution to remove Erythrosin. 



If considerable Orange I is present, some of it may contaminate 

 the washings containing the Ponceau 3 R and Naphthol yellow S, 

 especially when these have been separated by means of fourth- 

 normal hydrochloric acid after addition of gasoline. 



The fourth-normal hydrochloric acid washings of the amyl alcohol 

 may contain Indigo Carmine, Amaranth, and Tartrazin, their appear- 

 ance in most cases indicating which of these dyes may be present. 

 Instead of attempting to separate the dyes by fractionation the fourth- 

 normal hydrochloric acid solution may be evaporated to dryness, 



1 See also Price, U. S. Dept. Agr., Bur. Anim. Ind. Circ. 180. 



