THE COAL-TAR COLORS 133 



German universities produced a body of skilled manufacturers 

 and investigators who soon took the lead. At present, in 

 addition to the great factories near Berlin, Frankfurt, Elber- 

 feld, and Mannheim, and a host of smaller ones in various 

 parts of Germany, German capital controls many of the 

 establishments in France, Russia, and other countries. The 

 United States possess few independent factories, and the list 

 of their products is rather limited; indeed, American dyers ap- 

 pear to call for a smaller range of dyestuffs than those of other 

 countries. A peculiar development of the last fifteen years is 

 the extension of the methods of the dye industry to the 

 production of artificial drugs, such as antipyrin, antifebrin, 

 etc., many of which are manufactured in the same establish- 

 ments which control the dye patents. 



CLASSIFICATION. Artificial colors were formerly classified 

 merely according to the sources from which they were ob- 

 tained. Thus, many of them, including magenta, "aniline 

 blue," "aniline green," "aniline yellow," etc., were grouped 

 together as aniline colors. At present somewhat different 

 systems of classification are used by different authors, but all 

 systems are based exclusively on the chemical constitution 

 of the dyes. 



Many attempts have been made to find a general answer 

 to the question : What must be the chemical nature of a car- 

 bon compound in order that it may be a dye? An all-embrac- 

 ing answer to this question has not yet been found. But ex- 

 perience has shown that the true dyestuffs exhibit peculiar 

 groupings of the constituent atoms. Such "chromophore" 

 groupings produce, however, only a tendency toward color, 

 but not necessarily colors; indeed, many compounds con- 

 taining them are perfectly colorless, and the majority of true 

 dyes become colorless if deprived of the small amount of 

 oxygen they contain, although their chromophore groups 



