FOOD-COLOEIXG SUBSTAXCES. 11 



well. Many dyes exist in more or less associated condition in ordinar}^ 

 solutions. However, it is found in practice that in most cases the 

 distribution ratios with given acidity do not vary greatly, but that 

 fair results can be obtained on the assiunption that they will remain 

 constant,^ 



Both basic and acid triphenylmethane colors tend to undergo slow 

 intermolecular changes when treated with acids and alkalies (adjust- 

 ment of equihbrium between carbinol, imid, and ammonium forms) 

 and theii' complete separation by means of solvents is less simple than 

 that of most other classes. 



It will be noticed from the solubihty table, pages 22-33, that amyl 

 alcohol, amyl alcohol gasoline mixtures, and ether, although differing 

 greatl}"' in their power as solvents, show a sort of general correspon- 

 dence in properties. They are especially suited for fractionations of 

 such dyes as the sulphonated phenolic compounds, the distribution 

 ratios of these changing greatly with varying hydrogen ion con- 

 centrations. Dichlorhydrin, because of its solubility and non- 

 volatility, is not very convenient as a solvent; nevertheless, it is 

 almost indispensable for the separation of many colors. Anilin is 

 an excellent solvent, but usually must be completely removed from 

 a color solution before tests are made, and will be employed only 

 for a few separations. Both anilin and dichlorhydrin are con- 

 veniently' removed from water solutions by shaking out mth 

 carbon totrachlorid. 



It may bo remarked that in working with the coal-tar dyes the plan 

 of acidifying strongly, extracting, and then washing the solvent with 

 u more dilute acid, is in nearly all cases preferable to the practice of 

 gi-adually increasing the acidity and using a number of portions of 

 solvent. Much more solvent is required in this latter way, with a 

 corresponding increase in the proportion of the accompanying 

 impm'ities and in the difficulties caused by emulsification. 



The ■vvTitor usually prefers to begin the treatment with immiscible 

 solvents by shaking out with amyl alcohol from the neutral solution 

 aft(!r addition of some sodium cldorid. The outline which follows 

 will indicat<5 approximately the order in which the solvents will be 

 <;hoscn for a complex mixture, 



PROCEDURK OF SEPARATION. 



The Hf)lution of the foloring matter, as freo as possible from suspendod matter, is 

 treatofl farofully with wAJium farlxdiato if it contains free mineral acid or with acetic 

 a^id if it is alkaline, it should finally be neutral or very faintly acid. It should not 

 contiiin the f;oloring matter in too j^reat concentration, althouf^h when working with 

 extr-'utfl of food products this lattcjr condition is seldom encountered, (-oncentrations 

 of about O.Ol per cent may be taken a.s most suitable in general, and only in exco])- 

 tional cuM-a would stron>^(;r solutions (0.1 |)(;r cent, for instanc(f) be chosen by pr<;f- 



I Hw W. Ui^whT^ and C Hely, Zdl. f(ir (licm. iind TtkI. d. Koll. i;{ (I'.iKi;, %. 



