1902.] on Mecent Developments in Colouring- Matters . 107 



we are pleased to call leucocomponnds, are in the majority of cases 

 by no means colourless. Indigo-white itself is not white but yellow 

 in its alkaline solution which we call a vat. Other vat-dyes have 

 leucocompounds which are even more strongly coloured. Thus the 

 leucocompound of indanthrene, a beautiful new colouring-matter, 

 is blue like indanthrene itself; flavanthrene, a yellow dye-stuff, 

 which has not yet left the laboratory of its inventor, has a blue leuco- 

 compound. One may say, that with all vat-colours the real dye-stuff is 

 the leucocompound which is afterwards, when once fixed on the fibre, 

 transformed into a pigment by the oxidising influence of the air. 



In 1825 Faraday discovered, in this very house, benzene ; the 

 original specimen, prepared by his own hands, is before you. We 

 look upon it reverently, like on a sacred relic bequeathed to us by a 

 master-mind. But what a development has sprung from this first 

 attempt to unravel the mysteries of the aromatic series ! Our science 

 as well as our industry have been revolutionised by the investigation 

 of the derivatives of benzene, and the world has been embellished 

 by the gay and brilliant dyes of which it is the mother-substance. 

 The study of the chemistry of these dye-stuffs has become a domain 

 of science which, for variety and fascination, can hardly be surpassed 

 by any other. The deeper we penetrate into it the more it proves an 

 inexhaustible mine of the most subtle scientific thought, yet one 

 which never loses touch with practical life ; it is interesting alike to 

 the philosophical mind that wishes to revel in the wonderful perfec- 

 tion and order of nature, and to the philanthropic spirit which rejoices 

 in seeing many thousands of hands occupied and princely fortunes 

 produced by the utilisation of what was only a short time ago a refuse 

 and an encumbrance. It teaches a lesson even to those who are not 

 attached to science and apt to consider it as a kind of pastime for 

 people who lack ability for practical life. For they cannot help see- 

 ing that, in this case, the most intricate t-cience has led to something 

 eminently practical, commensurate to a standard which, though un- 

 known to the Bureau International des Poids et Mesures, is to some 

 people the only reliable one, viz. the one of £ s. d. 



I am afraid that the high praise which I feel justified in bestowing 

 on what has been the favourite pursuit of my life is not fully sub- 

 stantiated by the contents of this lecture. The subject which I had 

 to treat is so vast, that all I have been able to say is nothing but a 

 sketch or a programme of what would require a long series of lectures 

 if full justice were to be done to it. My one excuse for attempting 

 to sketch, in the short space of one hour, so vast a subject, is the place 

 in which I had the honour to speak : An audience that has been 

 addressed more than once by the pioneers of the chemistry of dye- 

 stuffs, by Faraday, Hofmann, William Perkin, and others, could, 

 from one of the Epigones, not have looked for more, than a few notes 

 and additions. 



[O. N. W.] 



