160 METHODS OF ANALYSIS [Chap. 



Scarlet (106) and Tartrazinc (94) appear when the washings have an acidity between 

 N/1 and N/4; Orange G (14) and Sohible Blue (480) between N/2 and N/16; Palatine 

 Scarlet (53), Ponceau 2R (55) and 3R (56), Naphthol Yellow S (4), Cochineal (706), 

 Crystal Ponceau (64) and Azorubine A (103) between N/IG and N/256. When the acid 

 is practically all removed, Orange I (85), Orange II (86) and Croceine Orange (13) 

 begin to wash out, and less readily. Orange IV (88) and Metanil Yellow (95). Finally 

 the unsulphonated coloring matters, such as Erythrosine G (516), Erythrosine (517) 

 and the Rose Bengals (520 and 523) are removed very slowly by water or not at all 

 when all traces of acid have been removed. Acid Yellow (8) and Brilliant Yellow 

 S (89) are not very uniform in composition. They are partially taken up by amyl 

 alcohol from acid solution and appear chiefly in the first washings. Indigo Carmine 

 (692) behaves somewhat similarly. 



Identification of the Coal Tar Dyesi^. 



1 2 general. 



The most widely used tests for the identification of coal tar dyes refer to the 

 changes produced with acids and alkalies. Other tests, based upon the behavior 

 with reducing agents, followed perhaps by treatment with oxidants or by separation 

 and identification of the reduction products^', and tests based upon oxidation of the 

 dye and treatment of the oxidation products^^ are generally applicable. Spectro- 

 scopic methods are also used^^. 



13 COLOR CHANGES PRODUCED WITH ACIDS AND ALKALIES. 



Transfer the separated coloring matter to wool (or silk in the case of oil-soluble 

 dyes) by boiling as directed in 2 (a) or 3. Care should be taken that the final dyeing 

 is made in a solution fairly free from foreign matter such as sugar or aromatic sub- 

 stances, which, adhering to the fiber, may modify the reaction. In most cases the 

 amount of color available is small and should not be dyed on too large a piece of wool 

 (or silk). Rinse thoroughly the dyed fibre in rmining water, dry, cut into small pieces 

 and place separately in the depressions of a white porcelain spot plate. Moisten the 

 pieces with the respective reagents employed. (For many coloring matters the 

 hue upon treatment with acids or alkalies varies markedly with the concentration 

 of the reagents and amount of dye present; therefore the unknown dye should be 

 compared with dyeings of known colors of approximately the same dye concentration 

 as shown by this appearance.) 



The table under 14 shows the color changes produced by concentrated hydro- 

 chloric and sulphuric acids, 10% sodium hydroxid and 12% ammonium hydroxid 

 solutions on wool dyed with 0.1-0.5% of the respective coloring matters. Included 

 also are the reactions of the oil-soluble colors but these refer to dyeings on silk. 

 The dyes are arranged approximately according to hue. Brown is classed with 

 orange, black (gray) with violet. 



