PRODUCTION OF DYES 327 



The chief colouring matter in madder is called alizarin, it is 

 accompanied by several others of which the most important is 

 named purpurine. Alizarin was isolated for the first time by 

 Robiquet and Colin in 1828. The composition of this substance 

 remained for many years a mystery. It was at one time supposed 

 to be a derivative of naphthalene, and many attempts were made 

 to produce it synthetically from that substance, but it was not 

 till about 1868 that its true nature was discovered and its con- 

 nection with anthracene was established. Anthracene is a 

 hydrocarbon, C 14 H 10 , which occurs among the least volatile 

 portions of coal-tar, and up to this time it had been totally 

 neglected and left in the pitch. Its relation to anthracene being 

 once known a key was obtained to its constitution, and in 1869 

 patents were taken out for its production by Caro, Graebe, and 

 Liebermann, followed only one day later by W. H. Perkin. 



This was the first natural colouring matter to be produced 

 synthetically and one of the most important, inasmuch as 

 alizarin and its derivatives and associates are employed in the 

 production of cotton prints all over the world, and are capable 

 of giving a great variety of colours. Here it must be explained 

 that alizarin and the allied colouring matter purpurine are often 

 referred to as adjective dyes, because they do not dye either 

 animal or vegetable fibre without previously impregnating the 

 fibre with some basic substance, such as alumina or oxide of 

 iron, chromium, or some other metal. The colouring matter 

 unites with such substances forming chemical compounds called 

 lakes which are insoluble in water. The metallic base introduced 

 is called a mordant, and each colouring matter produces a different 

 colour on the cloth by varying the mordant. Thus alizarin with 



Iron oxide gives a violet colour 

 Chromic oxide ,, brown ,, 

 Aluminium ,, bright red 



Dyes which attach themselves directly to the fibre are spoken of 

 as substantive dyes. 



A large amount of knowledge has been gained in recent times 

 as to the chemical constitution of the substances of which wool 

 and silk fibres are composed, and the facts have given much 

 assistance toward the conception of a comprehensive theory of 

 dyeing. For reasons to be explained later no one theory 



