SKETCH OF AUGUST WILHELM HOFMANN. 833 



Although Hofmann excels as a lecturer and teacher, his reputation 

 rests chiefly on his valuable and numerous contributions to the science 

 of organic chemistry, foremost among which are his investigations on 

 the coal-tar colors. 



He first began the study of the bases in coal-tar under the direction 

 of Liebig, and in 1843 we find him publishing his first original paper 

 on this subject. One of these bases, then known as "cyanol," at- 

 tracted his special attention, and by working over half a ton of coal- 

 tar he succeeded in obtaining this rare base in sufficient quantity to 

 investigate its properties, which he found to be the same as those of 

 "benzidam." Further investigation also enabled him to prove that 

 " aniline," the name then given to a substance that had only been ob- 

 tained from indigo by distillation, was identical with both cyanol and 

 benzidam. Here, then, were three sources for obtaining this rare ma- 

 terial. Evidently there could not be much of it in coal-tar, when only 

 three pounds could be separated from half a ton of tar ; indigo, too, 

 was an expensive source ; hence it was a fortunate circumstance that 

 Zinin had discovered another method of making it, and that too from 

 a far more abundant constituent of coal-tar, namely, benzol ; it is from 

 that all the aniline of the present day is prepared. 



Hofmann, it is said, noticed that aniline gave rise, under certain 

 conditions, to the production of a red color, but he failed to publish 

 the fact, and to Perkin belongs the credit of having discovered the 

 first aniline dye mauvine. This took place in 1856, and two years 

 later Hofmann discovered a red dye, then called Hofmann's red, which 

 was formed by the action of chloride of carbon upon aniline. Aniline 

 was beginning to attract the attention of manufacturers as well as of 

 chemists, and many different methods were devised for making what 

 seemed to be the same substance, a fine red dye variously known as 

 magenta, solferino, fuchsine, and aniline red. Hofmann undertook a 

 careful investigation of the dye, which resulted in his discovery of the 

 surprising fact that the red dye was in reality the salt of an organic 

 base, like an alkaloid, and that this base, to which he gave the name of 

 " rosaniline," was colorless. From this base he prepared another which 

 he called " leucaniline " by reducing it with zinc. Turning his atten- 

 tion to the blues, greens, and purples, he found them to be derivatives 

 from this same base, but of more complex construction. The impor- 

 tance of these investigations can scarcely be overestimated. The pro- 

 duction of dyes from aniline was no longer a matter of blind experi- 

 mentation ; empirical methods gave place to scientific ones, and the 

 process of making dyes has gone on to the present day nearly in the 

 same direction. One of the earliest practical results of this discovery 

 was the invention of a series of most beautiful purples which still 

 bear the name of Hofmann. Like Leverrier's discovery of Neptune, 

 their elements had been calculated beforehand, their existence fore- 

 told, and they needed only to be made. 



YOL. XXIV. 53 



