20 BULLETIN 448, U. S. DEPARTMEN'T OF AGRICULTURE. 



The original mixture, from v/hich. tlie seven colors described were 

 separated by adding acid and shaking out with amyl alcohol, may still 

 contain Light green S F yellowish, which will be colorless or nearly 

 so in the acid solution. To separate this dye the mixture is treated. 

 with strong ammonia or potassium hydroxid solution until slightly 

 alkaline, then neutralized with acetic acid. Any green that is pres- 

 ent will now be apparent by the color of the mixture and may be 

 extracted by shaking with a few small portions of dichlorhydrin. 

 After washing the dichlorhydrin extract with a httle water it should 

 be diluted with several volumes of benzene or carbon tetrachlorid. 

 The dye is then taken out with water. 



Besides the well-known reactions of acids and alkalies on the dyed 

 fiber or with the solution, a few tests may be mentioned as best 

 suited for the quick characterization of the different colors obtained 

 in this separation. Indigo Carmine is extracted in rather small pro- 

 portions from acid aqueous solutions by dichlorhydrin, differing in 

 this respect from nearly all the other common blue dyes. The bromin 

 test (p. 47) and the reactions with acids and alkalies usually are suf- 

 ficient for the identification of Tartrazin after its separation. New 

 Coccin (No. 106) and Ponceau 6 R (No. 108) are the only other com- 

 mon red dyes of solubility similar to that of Amaranth. Both are yel- 

 lowish in shade, the former markedly so. Ponceau 3 R, when treated 

 with barium chlorid and enough sodium acetate to neutralize any free 

 hydrochloric acid present, gives a bluish-red flocculent precipitate, 

 the supernatant liquid being left practically colorless. Ponceau 2 R 

 gives a carmine red precipitate; but most other red dyes of similar 

 solubihty do not form particularly insoluble barium salts. Naphthol 

 yellow S in solutions treated with an excess of ammonia or sodium 

 carbonate becomes intensely rose colored on addition of sodium hydro- 

 sulphite, the color gradually fading again as complete reduction takes 

 place. Orange I is well characterized by its solubfiity and behavior 

 with acids and alkalies. Erythrosin is perhaps best further iden- 

 tified by a test for iodin. Some of the color solution containing a 

 slight excess of alkali is evapora^ted to dryness, the residue heated to 

 redness, and the ash taken up with water and acidified with sulphuric 

 acid. Iodin may be tested for in the usual ways, such as with carbon 

 tetrachlorid a,nd a small drop of sodium nitrite, or with starch paste 

 and an oxidizmg agent. It is useless to test for iodin with very 

 small amounts of dye, but in most cases sufficient coloring matter 

 will be available to give satisfactory results. 



TREATMENT OF SOLUTION KESEEVED FOR TESTING FOE NATURAL COLORING 



SUBSTANCES. 



If coal-tar dyes have been found, the treatment for their separa- 

 tion will have given much information as to natural colors that may 

 be present. Many of the natural colors will have been separated in 



