COLORING MATTER. 



115 



As soon as the group is determined it is possible to carry the work further by refer- 

 ence to tables of coloring matter a in which the physical, chemical, and tinctorial 

 properties are given; but it is impossible for the published books to keep up with 

 the new dyes which are constantly being discovered, so that the tables are never 

 complete, although they will, as a rule, contain all the data necessary. 



Classification of organic coloring matters. 

 [A portion of the aqueous or alcoholic solution is treated with HC1 and SnCl 2 .] 



Complete decolorization. Reducible coloring 

 matters. Colorless solution is treated with 

 FeCl 6 or shaken, with exposure to air. 



The color changed no further than with HC1 

 alone. Nonreducible colors. A part of origi- 

 nal solution is mixed with 20 per cent KOH and 

 warmed. 



Schultz and Julius, Tabellarische Ubersicht der kiinstlichen organischen Farbstoffe; Allen, Com- 

 mercial Organic Analysis, 3d ed., Vol. Ill, pt. 1, pp. 529-665. 



