THE INFLUENCE OF RESEARCH ON THE 

 DEVELOPMENT OF THE COAL-TAR 

 DYE INDUSTRY.— Part II 



By FREDERICK ALFRED MASON, B.A. (Oxon), Ph.D. (Munich) 



Royal College of Science, South Kensington, London 



(Received for publication May 22, 191 5) 



The Third Period : 1 880-1 897. Substantive Dyes, and 



Research on Indigo 



Up to this date it was invariably necessary when dyeing 

 cotton to mordant it first (that is, to deposit certain metallic 

 compounds on the material by a preliminary treatment) in 

 order to render it capable of taking up the dye, whereas most 

 dyes, with the exception of alizarine, were capable of dyeing 

 unmordanted wool direct from a suitable dye-bath. 



The extra cost of mordanting the cotton was thus a serious 

 item, and in addition it was often very difficult to dye a mixed 

 cotton and wool material to a uniform depth of colour in both 

 materials. The announcement by Boettiger, therefore, in 1884 

 that he had succeeded in preparing a new red disazo dye-stuff, 

 which was named Congo red, capable of dyeing cotton directly 

 without the use of a mordant, might have been expected to 

 arouse the greatest interest ; but unfortunately the fact that 

 Congo red is very sensitive to acids (it is, in fact, much used 

 as an indicator for acids and alkalies) caused dyers to lose all 

 interest in it. 



It was soon found, however, that various other related 



dyes also had the power of dyeing cotton directly and possessed 



greater fastness than the original dye, so it was not long before 



systematic chemical investigations brought about the discovery 



of numerous direct or " substantive " dyes in all colours, and 



to-day we have a very large variety of such dyes in the market 



to choose from. 



412 





