ACHIEVEMENTS OF CHEMICAL INDUSTRY DUISBERG. 247 



cotton fabrics (after wasliing and exposure to light) and especially 

 of v>-all papei-s, of carpets, mbber material, and balloon coverings, 

 which the different firms of the German color and dyeing industry 

 have placed at my disposal for exhibition. 



If you now inquire how chemists have been able to make such 

 great progress, my only answer is by logical and untiring efforts 

 along well-known ways, undaunted by failures, and by diligently fol- 

 lowing any track, however faint, that gave promise of advance. 



In every branch of the color industry these methods have led to 

 faster and ever faster dyestuffs, from the multicolored benzidine 

 colors, described as fugitive to light and not stable to washing, to 

 the anthraquinone colors and the indigoid vat dyes. In all these 

 classes we have gradually learned to recognize certain regularities 

 and to accomplish certain results by systematically grouping the 

 components and fixing the position of the substituting groups, and 

 thus we have succeeded in increasing the fastness to light of the 

 individual chemical according to a preconceived plan. 



INDIGOID COLORS. 



The synthetic production of colors allied to indigo was stimulated 

 by the successful synthesis of indigo which almost entirely displaced 

 natural indigo and called the attention of both chemists and consumer 

 in an increased ineasure to the advantages of vat dyeing. The king 

 of dyestuffs, indigo, now finds itself in the company of a whole series 

 of other colors, the brome indigos, the thio indigos, a.nd alizarine 

 indigos, the shades ranging from blue to red, violet, gray, and black. 

 Even the ''purple" of the ancients has been reproduced by Paul 

 Friedlaender, who, by isolating the dj^eing principle found in certain 

 glands of the purple snail living in the Mediterranean, has demon- 

 strated the fact that this natural color is identical with a dibrom 

 indigo which had been long before produced synthetically. These 

 indigoid colors possess the same, if not better, properties as indigo 

 itself. 



ALIZARINE COLORS. 



The fastness of the alizarine colors, e. g., alizarine red, used lor 

 Turkey red, was well known in ancient times. But, wiiereas formerly 

 only mordant colors were considered to be fast, and consequently 

 only these were looked for in the anthraquinone group, which led to 

 the discovery of alizarine orange, brown, and blue, and the alizarine 

 cyanines, Robert E. Schmidt, in 1894 to 1897, succeeded in finding 

 acid-dyeing anthraquinone colors which dye every shade, rivalmg 

 the old and well-known triphenylmethanes in brightness and sim- 

 plicity of application and the alizarine mordant colors in their extra- 

 ordinary fastness to light, I merely mention alizarine cj'anine 



