XIJ COLORING MATTERS IN FOODS 157 



(C) Dilute 20-200 grams of the oil or melted fat with 1-2 volumes of gasoline and 

 shake out successively with 2-4% potassium or sodium hydroxid solution, 12-15% 

 hydrochloric acid, and phosphoric-sulphuric acid mixture, prepared by mixing 

 85% phosphoric acid with about 10-20% by volume of concentrated sulphuric acid. 



The dilute alkali extracts Sudan G and Annatto. The dilute hydrochloric acid 

 extracts Aniline Yellow (7), Aminoazotoluene, and Butter Yellow {16), the first 2 

 forming orange-red, the latter cherry-red solutions in this solvent. Benzeneazo- 

 beta-naphthylamin and homologues also come in this group, though they are not 

 extracted very readily and decompose rapidly on standing in strongly acid solution. 

 The phosphoric acid mixture is necessary for the extraction of Sudan I (11), Sudan 

 II (49), Sudan III (14^), and the homologue of the last, Sudan IV. The procedure 

 is not very suitable in the presence of Auramine but this dye is seldom found in oils. 

 Neutralize the alkaline and dilute hydrochloric acid solutions; dilute the phosphoric 

 acid mixture and partially neutralize, cooling the liquid during this operation; 

 and extract the dyes by shaking with ether or gasoline. 



For the direct dyeing test use the alcoholic solution, obtained as directed in (a). 

 Evaporate to dryness the ether or gasoline solutions, obtained as directed in (b) and 

 (C), and dissolve the residue in 10-20 cc. of strong alcohol. To the alcoholic solution 

 add some strands of white silk and a little water and evaporate on the steam bath until 

 the alcohol has been removed or until the dye is taken up by the silk. The dyeing 

 test is sometimes unsatisfactory and in all cases a small portion of the alcoholic solu- 

 tion should be tested by treating with an equal volume of concentrated hydrochloric 

 acid and stannous chlorid solution. The common oil-soluble coal tar dyes are ren- 

 dered more red or blue by the acid and are decolorized by the reducing agent. Most 

 of the natural coloring matters become slightly paler with the acid and are little 

 changed by the stannous chlorid solution. 



Separation of Coloring Matters in Pure Condition by Means of 

 Immiscible Solvents''. 



4 preparation of sample. 



(a) Water-soluble colors. — Proceed as directed under 2, omitting the fixation of 

 the color on wool, and obtain an aqueous solution as free as practicable from sus- 

 pended matter, alcohol, acids, alkalies and salts. 



(b) Water-insoluble lakes. — If the sample is in solid form, treat the well divided 

 material with sufficient water to form a paste. Liquids require no preparation 

 except the removal of alcohol when present. 



5 Mixtures of Orange I, Erythrosine, Indigo Carmine, Amaranth, 



Tartrazine, Naphthol Yellow S, Ponceau 3R and 

 Light Green S F Yellowish. 



The use of immiscible solvents for the separation of mixtures of coloring matters 

 usually involves a systematic fractionation since many of the dyes used do not differ 

 very greatly in their solubilities in the various solvents. When it seems probable 

 that only the 8 coal tar dyes permitted under the Federal Food and Drugs Act^ 

 are present, the following abridged procedure may be used for their separation. For 

 this procedure the concentration of the dye solution should lie preferably between 

 0.01-0.05%. The solutions obtained in the examination of colored food products 

 practically never require further dilution but with commercial food colors care must 

 be taken that the concentration is not too high. Treat the sample, prepared as 

 directed in 4, with one half its volume of concentrated hydrochloric acid and extract 

 a few times with amyl alcohol. The use of the centrifuge is sometimes necessary 



