PAINTS, DYES, AND VARNISHES 



1868, when Graebe and Liebermann effected the syn- 

 thesis of alizarine, which proved the death knell to the 

 madder industry. Ten years later Baeyer produced 

 indigo commercially the beginning of the downfall of 

 the natural product. Since then important practical 

 discoveries have followed each other with bewildering 

 rapidity. Something like four hundred coal-tar colors 

 are now in use for the manufacture of lakes ; and the end 

 is not yet. 



The amount of coal-tar available in ordinary coal is 

 relatively small, the proportion being about one to 

 twenty. But in the aggregate this amount suffices to 

 supply the demand. The coal-tar colors on the market 

 are usually in the form of a powder or crystals, the shade 

 of which may be quite different from the solution. All 

 of them are very complex chemical compounds, many 

 of which, although identical in the number and kind of 

 atoms in their molecules, are very different in color. 

 The explanation of this seems to be in the arrangement 

 of the atoms rather than in their number in each mole 

 cule, but the exact nature of this peculiarity has not been 

 determined as yet. After all, it is no more wonderful 

 or difficult to understand that two substances, each 

 having six atoms of hydrogen and seven atoms of carbon 

 in each molecule, should, let us say, be blue and red 

 respectively, than, to take a familiar example, that the 

 chemically identical substances, charcoal and diamond, 

 should be, one colorless and the other jet-black. 



The color-maker's interest in these coal-tar colors 

 lies in their application to making lake pigments. In 

 this process there is a very distinct and definite chemical 



