SCIENCE IN THE INDUSTRIAL WORLD 



action, which the manufacturer can produce with un- 

 failing certainty; and yet "the theory of the formation 

 of lake pigments has not been clearly enunciated." In 

 many lakes there is this distinct chemical action, but 

 not chemical combination. The salts used cause pre- 

 cipitation, but not in the definite proportions that would 

 result from chemical combination. Variation in the 

 relative amounts of the color and the salt causes varia- 

 tion in shade and color; but as this variation is con- 

 stant, it is a concern of the chemist rather than of the 

 practical manufacturer to determine the exact chemi- 

 cal action. 



Many colors are produced by the combined precipi- 

 tation of several salts and colors; and since so many 

 colors are now known, the possibilities of combined 

 precipitation are practically without limit. 



DYES 



While the various artificial colors, such as those 

 made from coal-tar and those synthesized from other 

 substances, are gradually revolutionizing the use of 

 pigments in all fields where colors are used, a similar 

 revolution has already been effected in the field of dye- 

 ing fabrics. Natural coloring-matters, such as cudbear 

 and logwood, which were formerly among the main- 

 stays of the dyers, are now seldom used. For the 

 artificial colors not only give a wider range of colors and 

 shades, but are cheaper, and very much easier to use. 

 It was as dyes, rather than as pigments for painting, 

 that they were first introduced ; and while their applica- 



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