September 6, 1895.] 



SCIENCE. 



291 



proportions with tlie pure toluidine from 

 Muspratt, the proportions corresponding 

 with one molecule of benzene to two mole- 

 cules of toluene, the red color was promptly 

 produced. In this connection Hoffmann said 

 'the industry was ahead of the science' and 

 Caro said : ' ' Hence the industry was not only 

 the generator of aniline red, but further- 

 more it had opened up the way to the ra- 

 tional utilization of benzene and its homo- 

 logues for all present and future uses of 

 color manufacture." 



Artificial alizarine has much the same 

 kind of history. It was developed by 

 Graebe and Liebermann by most rational 

 methods and from the constitution and re- 

 actions of the body itself. Starting with a 

 commercial body, produced by industrial 

 methods and in most empirical ways, they 

 endeavored to reproduce it by rational 

 synthesis and succeeded. Their method 

 through dibromanthraquinonewas not, how- 

 ever, a commercial possibilitj', and it re- 

 mained for Perkin, with his industrial ex- 

 perience and cajDacity, and his engineering- 

 skill combined with his knowledge of chem- 

 istry, to overcome the manufacturing diffi- 

 culties and to attain this end by other 

 means and reactions than had been pro- 

 posed by Graebe and Liebermann. The 

 process proposed by the latter was precluded 

 by the high cost of bromine and Perkin re- 

 placed it by sulphuric acid, producing 

 the anthraquinone sulphonic acids which 

 yielded after the melt the product desired. 

 The industrial genius of Perkin gave arti- 

 ficial alizarine and with it a long series of 

 products and problems for study and solu- 

 tion by chemists everywhere. It taught re- 

 actions that were fertile in stimulating new 

 research and established facts that could 

 not be, or at least were not, discovered in 

 the laboratory. For instance, in the course 

 of the manufacture, Perkin found that 

 when, as sometimes happened, sulphona- 

 tion of the anthraquinone was not thor- 



oughly effected through insufficient heating 

 or use of too little acid, a really better pro- 

 duct was obtained than when the process 

 had proceeded normally. He found that 

 in the latter case the color of the resulting 

 product was less brilliant than when these 

 irregular conditions prevailed ; that, in the 

 latter, the resulting paste was a mixture of 

 colors, while with the former nearly pure 

 alizarine was the result. Investigation con- 

 firmed the outcome of the practice and 

 showed that fi-om the anthraquinone mono- 

 sulphonic acid only pure alizarine was pro- 

 duced, while from the result of higher sul- 

 phonation a mixture of products was se- 

 cured. Such a discovery may have been 

 possible only in the larger way occurring in 

 the woi'ks and might have long been over- 

 looked in the laboratory. At any rate it 

 was brought out in the industrial operation 

 of the reaction, and a new fact was added 

 to the sum of knowledge. 



This discovery brought further necessity 

 and new invention. By the ordinary 

 method of sulphonating then employed, the 

 monosulphonic acid could not readily be 

 produced and it remained for Perkin to ad- 

 vance both science and technology still fur- 

 ther by the determination of a new process 

 for attaining this end. He found* that 

 dichloranthracene which is easily made may 

 be as easily sulphonated and that the di- 

 chloranthracene sulphonic acid is readily 

 converted to the anthraquinone sulphonic 

 acid by heating with sulphuric acid, the 

 final result depending upon the degree of 

 heat employed in the reaction in sulphona- 

 ting the dichloranthracene. He had thus 

 not only advanced the industry in this 

 branch of manufacture, but he had added 

 to the list of reactions and compounds in 

 chemistry as well. 



Hoffmann received from the French color 

 works the queues d^aniline, from which he 

 was able to separate para toluidine and the 



* Jour. Soc. Arts. 1879. 577. 



