FOOD-COLOEING SUBSTANCES. 7 



diluted with a few volumes of gasoline. Shaking out one or two 

 times will usually be sufficient, but the method is not applicable to 

 colors such as tolueneazo-jS-naphthylamin, which are sensitive to 

 strong acids. The alkali salts of Sudan G and of the coloring matter 

 of annatto are readily soluble in water; hence these dyes are most 

 easily removed by shaking out with dilute sodium or potassium 

 hydroxid solution. 



The extraction and separation of the dissolved coloring matters 

 may be carried out together as follows : The oil or melted fat is diluted 

 with gasolme and shaken out first with 2 per cent (haK-normal) 

 sodium hydroxid solution to remove annatto, Sudan G, and colors 

 of similar solubility. The mixture is then washed several times, if 

 necessary, with hydrochloric acid of from four to six normal strength, 

 which will take out the aminoazo derivatives, such as Butter YeUow 

 and ammoazotoluene. Benzeneazo-/3-naphthylamin and tolueneazo- 

 jS-naphthylamin are extracted rather slowly by this treatment, the 

 dyes apparently suffering rearrangement from the hydrazo-imin 

 form into the true azo form before going into solution in the acid. 

 Since the toluene derivative especially is rather rapidly decomposed 

 by hydrochloric acid, the extracts should not be allowed to stand, 

 but should be neutralized immediately. The Sudans and similar 

 colors not extracted from the mixture by alkali or acid should be 

 separated by one of the general procedures described on page 6, 

 most conveniently with the phosphoric acid mixture. If the phos- 

 phoric acid solution, after washing once or twice with gasoline, be 

 diluted and partially neutralized, the coloring matter in quite pure 

 condition can be obtamed by extraction with ether or gasoline. 



Glycerol,^ sodium salicylate ^ solution, and a mixture of these two 

 have been recommended for the extraction of colors from some food 

 products. 



Microscopic examination of colored products usually gives useful 

 mforaiation. This is especially true in certain cases for chemical 

 tests under the microscope.'' 



CertaLn coloring matters can not be brought into solution by the 

 methods outlined. Such substances are the organic pigments Indan- 

 thrcne (No. 569) and unsulphonated indigo (No. 690), which are 

 insoluble in all ordinary solvents and must be identified by their 

 general properties. Lampblack and similar forms of carbon are 

 characterized by insolubility in acids, alkalies, or hot dichlorhydrin, 

 and by their complete combustibility. Ultramariue is stable toward 

 iJkidics but is very readily decobjrized with acids with evolution of 

 hydrogen sulphid, which may be detected with lead acetate paper. 



' Kllngor uml Bujard, '/.. An(!f!W. Choiri. (IHOI), r.lf). 



» K. Sfwolh, '/.. Nahr. ficnuHsm. IH {Vm.)), .WT. 



» WInton, A. L., The. Micnneopy of Veyelable Foodn. Now York, JUIO. 



