Natural Colouring Matters and their Analogues

Abstract

THE chemist has been attracted to the investigation of natural and artificial colouring matters for a variety of reasons, including not only colour-pleasure, the incentive of the knowledge that chlorophyll and haemoglobin perform some of the most important functions in vital processes, and the industrial importance of dye-stuffs and pigments, but also on account of the fact that visible colour more than any other property facilitates the experimental study of organic substances whether by analysis or synthesis. It furnishes a standard of homogeneity or a measure of concentration, it is an invaluable guide in the search for methods of separation and purification, and it at once indicates, by its appearance or disappearance, the occurrence of a chemical reaction. Small wonder that the successful outcome of the investigation of many colourless substances has awaited the discovery of some characteristic colour-reaction; a noteworthy example being vitamin A.