156 METHODS OF ANALYSIS [Chap. 



tion to remove the excess of ammonia, drop in a piece of clean, wet wool, make dis- 

 tinctly but not strongly acid with hydrochloric acid and boil again. If acid coal 

 tar dyes are present, they will usually give a fairly clean, bright dyeing on the second 

 piece of wool. A further purification may be carried out by repeating the stripping 

 and re-dyeing, though generally accompanied by corresponding loss of dye. 



(b) Candies and similar colored sugar products. — Dissolve about 20 grams of the 

 sample in 100 cc. of water and treat the solution as directed under (a). When the 

 coloring matter is on the surface of the candy, pour off the solution before the color- 

 less inner portion has dissolved. 



(C) Jams and jellies. — Boil a mixture of 10-20 grams of the sample and 100 cc. 

 of water with wool in neutral and also in acid solution as directed under (a). For 

 thick jams it is usually better, though less easy, first to extract the coloring sub- 

 stances by treating the product as directed under (d). 



(d) Canned and preserved fruits and vegetables, sausage casings, smoked fish, coffee, 

 spices, etc. — Macerate 20-200 grams of the sample with 4-5 times its weight of 80% 

 alcohol. After standing a few hours pour off the solvent as completely as possible 

 and repeat the extraction, using 70% alcohol containing about 1% of ammonia. 

 (1) Examine separately the filtered alcoholic extracts as directed under (a); or, (2) 

 Boil the ammoniacal solution until practically neutral, complete the neutralization 

 with acetic acid, add the neutral 80% alcohol extract, continue the evaporation 

 until most of the alcohol is removed, and boil with wool as directed under (a). 



(e) Cocoa and chocolate products. — Treat cocoa as directed under (d). The alco- 

 holic extract will contain a large amount of natural coloring matter and several 

 dyeings and strippings may be necessary to get rid of this in order to show the pres- 

 ence of coal tar dyes. 



Chocolate may be treated similarly but the following procedure is preferable: 

 Wash 20-200 grams of the well divided sample with gasoline on a filter until most of 

 the fat has been removed; if the gasoline is colored, reserve for the examination of 

 oil-soluble dyes as directed under 3. Remove most of the adherent solvent from the 

 residue by evaporation or pressure between layers of absorbent paper and digest 

 with alcohol as directed under (d). 



Coal tar dyes may also be detected in chocolate and cocoa products by mixing 

 directly with 3-4 times their weight of hot water and immediately boiling the magma 

 with wool, as directed under (a). Because of the presence of large amounts of fatty 

 and protein materials, this method is not very satisfactory. 



(f) Cereal products. — Proceed as directed under (d), in most cases working with a 

 large amount of the sample, 200-500 grams, and a relatively smaller amount of alcohol. 

 Where tests are to be made only for the acid dyes, the extraction with neutral 

 80% alcohol may be omitted advantageously. 



3 OIL-SOLUBLE DYES\ 



Prepare an alcoholic solution of the oil-soluble dye by one of the following methods 

 which are to be applied to the oil or fat obtained by extraction with ether or gasoline 

 if the nature of the substance requires it : 



(a) Shake the oil or melted fat with an equal volrnne of 90% alcohol. The alcohol 

 after separation will contain Aniline Yellow, Butter Yellow, Aminoazotoluene and 

 Auramine, if present. 



(b) Saponify 20-200 grams of the oil or fat with alcoholic potash and, after re- 

 moval of most of the alcohol on the steam bath, extract the soap with ether or gaso- 

 line. Most of the common dyes are removed by this treatment, though the digestion 

 with strong alkali may cause some decomposition and make the extraction rather 

 troublesome. 



