Colour Production and Chemical Constitution

Abstract

TN the Proceedings of the U.S. National Academy of Sciences for September 15, 1523 (vol. 9, p. 303), Prof. Julius Stieglitz, of the University of Chicago, puts forward in outline a theory of colour, which is based upon the electronic theory of valency, but can for the most part be discussed apart from that theory. His fundamental suggestion is that Otto Witt's chromophoric or “colour-carrying “groups are essentially oxidising radicals and that the auxochromic or “colour-intensifying “groups are essentially reducing radicals. He is impressed by the fact that nearly all dye-stuffs contain both of these opposite constituents, and seeks for a key to the origin of colour in the well-known fact that all dye-stuffs on reduction yield colourless leuco-bodies, which therefore usually contain two reducing and no oxidising centres. He illustrates his argument by reference to the case of indophenol, thus: