XI] COLORING MATTERS IN FOODS 159 



the Yellow from the combined ethyl acetate extracts by shaking with water. Naph- 

 thol Yellow S is almost colorless in strongly acid solutions, and its absence in wash- 

 ings, etc., must never be assumed until these have been made alkaline. Finally 

 separate the Ponceau 3R from the acid solution by shaking with amyl alcohol, and 

 then wash out the dye from this extract with a few small portions of water. If, 

 in the case of mixtures containing Orange I, the washings of the ethyl acetate, which 

 should contain only Naphthol Yellow S, become more red upon the addition of al- 

 kalies, combine, then (1) Make N/4 with hydrochloric acid and remove the contami- 

 nating Orange by shaking with amyl alcohol-gasoline mixture (1 to 1); or, (2) Treat 

 the combined washings mth one fifth their volume of concentrated hydrochloric 

 acid, extract the dyes by shaking once with amyl alcohol, and remove the Yellow 

 by washing with several portions of 5% salt solution. 



9 LIGHT GREEN S F YELLOWISH. 



The original mixture, A, under 5, from which the above mentioned 7 colors have 

 been removed 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 treat the mixture with strong ammonia or potassium hydrox- 

 id solution until slightly alkaline, and neutralize with acetic acid. Any Green 

 present will now be apparent by the color of the mixture. Extract the color by 

 shaking with a few small portions of dichlorhydrin. Wash the dichlorhydrin extract 

 with a little water, then dilute with several volumes of benzene or carbon tetra- 

 chlorid, and remove the dye by shaking with water. 



When coal tar dyes other than the 8 mentioned above are present, the solutions 

 obtained in this procedure will be found to contain a coloring matter which does not 

 correspond exactly in properties to one of the dyes named above. When coal tar 

 dyes other than these 8 are present, reference should be made to the larger works'. 



Coal Tar Dyes in General. 



10 basic dyes. 



Most basic dyes may be separated from mixtures by making alkaline with sodium 

 hydroxid and shaking with ether'". Use the sample, prepared as in 4, for this pur- 

 pose. Separate the ether layer, which may or may not be colored, and shake with 

 2-5% acetic acid, which will take up any dye present, forming a colored solution. 

 Although the common basic colors undergo some alteration by this treatment", 

 it may be used for the qualitative detection and separation of Methyl Violet B {4-51), 

 Magenta {U8), Bismarck Brown (197), Malachite Green (427), and Rhodamine B 

 (504). With care Auramine (425) may also be separated in this way though it is 

 quickly decomposed on standing in alkaline solution. 



11 ACID DYES. 



The following short procedure is often convenient for the examination of mixtures 

 of acid dyes: Make the sample, prepared as in 4, the color concentration of which 

 does not vary greatly from 0.01-0.05%, strongly acid by adding one half its volume 

 of concentrated hydrochloric acid and shake with amyl alcohol. Separate the 

 amyl alcohol solution and wash by shaking with successive portions of one half its 

 volume of water, reserving the portions in separate test tubes or beakers. Because 

 of the acid dissolved in the amyl alcohol these washings will show a regular decrease 

 in acidity and the coloring matters will appear in maximum amount in the different 

 fractions according to their respective solubilities. Ponceau 6R (108) is washed 

 out chiefly while the acidity is still high, N/1 or above. Amaranth (107), Brilliant 



