FOOD-COLORING 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-/3-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 gasoline and shaken out first with 2 per cent (half-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 Yellow 
and aminoazotoluene. Benzeneazo-,3-naphthylamin and tolueneazo- 
/3-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 obtained by extraction with ether or gasoline. 
Glycerol, 1 sodium salicylate 2 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 
information. This is especially true in certain cases for chemical 
tests under the microscope. 3 
Certain coloring matters can not be brought into solution by the 
methods outlined. Such substances are the organic pigments Indan- 
threne (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. Ultramarine is stable toward 
alkalies but is very readily decolorized with acids with evolution of 
hydrogen sulphid, which may be detected with lead acetate paper. 
i Klinger and Bujard, Z. Angew. Chem. (1891), 515. 
2 E. Spaeth, Z. Nahr. Genussm. 18 (1909), 587. 
3 Winton, A. L., The Microscopy of Vegetable Foods. New York, 1916. 
