318 CHEMICAL DISCOVERY AND INVENTION 



this high position ? The answer has been given repeatedly since 

 1880 when Germany had already succeeded in carrying off a 

 large part of the business of manufacturing colours from coal-tar 

 from England to the Continent. In the repeated warnings which 

 have been issued since that time in no uncertain voice by Meldola, 

 Green, the Perkins (father and son), and many other English 

 chemists, two causes for the change have invariably been indi- 

 cated, first the neglect of organic chemistry in the universities and 

 colleges of this country, and then the disregard by manufacturers 

 of scientific methods and assistance and total indifference to the 

 practice of research in connection with their processes and 

 products. As to the former no such charge can now be brought 

 against the chemical schools of this country. Manufacturers 

 have been aroused and many have taken steps in the direction 

 of reform, but whether any considerable proportion of the colour 

 industry, so long departed, can be brought back again, time alone 

 will show. 



It will now be evident that not only are the dyes not present 

 in coal-tar ready formed, but that the hydrocarbons which are 

 present in coal-tar and are got out of it, as already explained, by 

 distillation, are converted into the colouring matter by under- 

 going successive chemical changes whereby several intermediate 

 products are formed. The intermediate compounds if merely 

 mixed together would not produce a dye, but when acted upon 

 by chemical agents each one loses a portion of one of its con- 

 stituents, the hydrogen for instance, and receives something in 

 place of it, and a new compound or association of atoms is formed 

 which has properties different from the properties of the separate 

 materials concerned. Thus a molecule of aniline, C 6 H 5 NH 2 , one 

 of orthotoluidine, C 7 H 7 NH 2 , and one of paratoluidine, C 7 H 7 NH 2 , 

 when attacked by three atoms of oxygen jointly lose six atoms 

 of hydrogen, while the three altered residues combine to form 

 rosaniline. Pararosaniline is produced in like manner when a 

 mixture of aniline and paratoluidine is attacked by oxygen. 

 Equations representing these changes may be written as follows : 



PTT -I PTT 1 



(WNH,+q,Hi<Sii 4+C 6 H 4 < ^ '+30 = 



Aniline. Paratoluidine. 



3H 2 0+C 20 H 1? N 3 



Rosaniline. 



