January 3, 19U2.] 



SCIENCE. 



9 



From 1858 to 1886 may be called the 

 ' rosanilin period ' of the color industry, 

 since it was chiefly marked by the develop- 

 ment of the colors of this group. A few 

 individual members of other groups had 

 been discovered, but had not attained im- 

 portance. This is especially true of the 

 ' azo ' dyes, which have attained such im- 

 portance that the last fifteen years may 

 justly be called the ' azo period. ' The 

 number of individual compounds belonging 

 to this class which have either been pre- 

 pared or are at present preparable, runs 

 into many millions, and far exceeds the 

 members of all other groups of coloring 

 matters put together. In commercial im- 

 portance, also, they occupy a position at 

 present far in advance of any other group ; 

 the - employment of some of them, as the 

 azo blacks, amounting to many thousands 

 of tons annually. A great stimulus to the 

 investigation of the azo compounds was 

 given by the discoverj^ by Boettger in 1884 

 of the first color possessing a direct affinity 

 for cotton (Congo red), which was followed 

 in a few years by a rapidly increasing 

 series of colors of all shades having similar 

 dyeing properties. The great simplification 

 of cotton dyeing, brought about by the 

 introduction of the new group of azo colors 

 — 'benzo' or 'diamin' colors as they are 

 called— led to a rapid increase of their 

 number. Simultaneously therewith pro- 

 ceeded the discovery and investigation of 

 the various isomeric derivatives of naphtha- 

 lene, required as raw products for the prep- 

 aration of these colors. 



Another method of applying azo colors 

 to cotton, by which much faster shades are 

 obtained, was introdiiced by Messrs. Read, 

 HoUiday & Co., of Huddersfield, in 1880, and 

 consisted in producing unsulfonated azo 

 compounds on the fiber by direct combina- 

 tion. Owingto technicaldifficultiesthisproe- 

 ess has only reached its full development 

 during the last few years, and that at other 



hands than those of its discoverers. The 

 most important color produced by this 

 method is paranitranilin red, for whichever 

 two hundred tons of chemically pure para- 

 nitranilin are manufactured annually. 



The search for direct cotton colors led the 

 author to the discovery of primulin in 1887, 

 and this can be used for the synthesis of 

 various azo colors on the fiber, which are 

 remarkable for great fastness in washing. 

 The new principle of dyeing which this in- 

 troduced has been considerably extended in 

 other so-called ' diazo ' colors. The mordant 

 azo colors have also, with the growing de- 

 mand for faster shades, recently come into 

 much prominence. The laborious scientific 

 investigations of Fischer and Hepp,Bernth- 

 sen, Kehrmann and others on the azins, 

 oxazins, and thiazins, have led to the dis- 

 covery of many valuable new members of 

 these classes, such as the indulins, rosindu- 

 lins, rhodulins, etc. Much investigation 

 has also been given to the pyrone and acri- 

 din groups, leading to the rhodamins, a 

 class of pure basic reds, and to the basic 

 yellows and oranges. 



Next to the azo group, it is in the alizarin 

 group that the greatest progress must be 

 recorded. The demand for fast colors for 

 calico-printing and for dyeing chrome-mor- 

 danted wool to Avithstand severe milling 

 operations, has led to a long series of inves- 

 tigations and patents for producing new 

 derivatives of anthraquinone— the anthra- 

 cene and alizarin colors. The ' Vidal ' 

 blacks and other colors, for the direct dye- 

 ing of iinmordanted cotton, are now being 

 rapidly developed, although thus far their 

 constitution has resisted elucidation. 



It may be fairly claimed, however, that 

 the greatest triumph of the coal-tar in- 

 dustry for the past fifteen years has been 

 the successful production of artificial in- 

 digo on a large manufacturing scale. 



Returning to the economic aspect of the 

 subject, I will ask you to consider what 



