14 BULLETIN 448, U. S. DEPAETMEXT OF AGEICULTUEE. 



By reduction in ammoniacal solution, avoiding excess of "Blankite," No. 106 and 

 No. 107 may be destroyed, while No. 8 is merely converted into the hydrazo com- 

 poimd and may be restored by shaking with aii\ No. 692 is destroyed by -warming 

 in acid solution containing a little ui-ea and a drop of sodium nitrite solution, while 

 Nos. 106, 107, and 108 are scarcely attacked. The cyanid reaction is best suited for 

 the examination of mixtm'es of No. 106 and No. 107. 



The dyes of this group, because of their ready solubility in water and fruit juices, 

 are well adapted and largely employed for food coloring. Hence the application of 

 the data given in the solubility table, etc., has been indicated rather more fully here 

 than for the other classes. 



Sec. 7. The amyl alcohol extract after being washed with foui-th-normal hydro- 

 chloric acid may be similarly washed with sixteenth-normal hydrochloric acid; 

 although unless No. 14 or No. 188 appear to be present this step usually will be 

 omitted. 



Sec. 8. The amyl alcohol is now measm'ed, diluted with an equal volume of low- 

 boUing-point gasoline, and washed first with foiu-th-normal hydrochloric acid two or 

 three times, then si m ilarly with sixteenth-normal hydrochloric acid, with sixty- 

 foiu'th-normal hydrochloric acid, with sixty-foru'th-normal acetic acid, and finally 

 with sixty-foui'th-normal sodium hydroxid. The dyes separated here include a 

 large number of indi\'iduals and the treatment most desirable for any given mixture 

 can best be judged after reference to the tables, pages 24 to 29. Obviously, the 

 normalities stated are chosen somewhat arbitrarily, any two dyes contiguous in the 

 table usually differing little from each other in solubility. When the appearance, etc. , 

 of the different fractions indicate the presence of more than one dye, the coloring mat- 

 ters must be obtained in pure condition by refractionation. Although the acid amy! al- 

 cohol extract, after dilution with gasoline, appears to yield all its color to the acid wash- 

 ings, it must nevertheless be shaken with the alkahne solution before being discarded, 

 since a number of the weakly acid coloring matters (most of which, it is true, do not 

 properly come in this group) are nearly colorless when dissolved in the neutral or acid 

 organic solvent. 



Naphthol yellow S, which predominates in the first strongly acid washings, is also 

 nearly colorless in acid solutions, and a portion from these solutions must always Ije 

 tested for this dye by making double normal with hydrochloric acid and shaking with 

 washed ethyl acetate. If the separated solvent is found by treatment with alkali to 

 have taken up a yellow dye , the remainder of the fractions containing it are treated in the 

 same way with the acetate. Although the washings of low acidity may contain some 

 coloring matters, the major portion of such dyes will be in the amyl alcohol extract 

 of the neutral salt solution. It is best, therefore, to set aside the sixty-fourth-normal 

 acetic acid and the sixty-fourth-normal sodium hydroxid washings until after the 

 examination of the neutral salt amyl alcohol extract has been made; or these solutions 

 may be mixed with the corresponding ones obtained by the processes outlined in 

 sections 11 and 12 and may be worked up with them. Or, finally, the amyl alcohol 

 gasoline mixtiu'e, after washing with sixty-fourth-normal hydrochloric acid, may be 

 reserved and combined with the similar mixtiu-e described in section 10. 



Sec. 9. For the separation by chemical means of closely similar dyes of these 

 gTOups some of the more useful general methods may be indicated here. 



The reaction Avith cyanid (page 52) may be used for the separation of R-salt deriva- 

 tives (Nos. 55, 56, 65, 15) from mixtures with isomers. 



Methods based on reduction and subsequent oxidation are applicable for the destruc- 

 tion of azo and nitro colors in presence of most other classes of colors, as indicated in 

 the tables of Weingartner and of Rota. 



By cautious reduction in sodium carbonate or ammoniacal solution oxyazo dyes 

 tend to be attacked more rapidly than aminoazo dyes. It must be remembered. 



