TRANSACTIONS OF THE SECTIONS. 57 



phthalic acid can be produced from botli of them ; and many were the experiments 

 made by chemists in this direction ; it was not, however, until 1808 that this was 

 proved to be a mistake, and its relationship to anthracene was discovered by Graebe 

 and Liebermann, who succeeded in preparing this coal-tar product from the natural 

 alizarin itself. 



Having obtained this important result, they turned their attention further to the 

 subject, hoping to find some process by which alizarin could be produced from 

 anthracene ; in this they were soon successful. 



The discovery of the artificial formation of alizarin was of great interest, inas- 

 much as it was another of those instances which have of late years become so 

 numerous, namely the formation of a vegetable product artificially ; but the process 

 used by Graebe and Liebermann was of little practical value, because too expensive 

 for practical purposes. 



Ha-^ing previously worked on anthracene derivatives, it occurred to me to make 

 some experiments on this subject, which resulted in the discovery of a process by 

 which the colouring-matter could be economically produced on the large scale : 

 Messrs. Caro, Graebe, and Liebermann about the same time obtained similar 

 results in Germany ; this was in 18G9. Fm-ther investigation during that year 

 yielded me a new process, by which " dichloranthracene '' could be used in 

 place of the more costly product anthraquinone, which was required by the 

 original processes. I mention this, as most of the artificial alizarin used in this 

 country up to the end of 1873, and a good deal since, has been prepared by this 

 new process. 



It was observed that when commercial artificial alizarin prepared from anthra- 

 quinone, but more especially from dichloranthracene, was used for dyeing, the 

 colours produced difl:ered from those dyed with madder or pure alizarin ; and many 

 persons therefore concluded that the artificial colouring-matter was not alizarin at all. 

 This question, however, was set at rest by separating out the pure artificial alizarin 

 from the commercial product and compaiing it with the natural alizarin, when it 

 was found to produce exactly the same colours on mordanted iiibrics, to have the 

 same composition, to give the same reactions with reagents, and to yield the same 

 products on oxidation. 



But whilst examming into this subject it was foimd that a second colouring-matter 

 was present in the commercial product, and in somewhat large quantities, especially 

 when dichloranthracene had been employed in its preparation ; and to this was due 

 the difierence in shade of colour referred to. 



This substance, when investigated, was found to have the same composition as 

 "purpurin," also a colouring- matter found in madder, but of very little value on 

 account of the looseness and dulness of some of the colom-s it produces. This new 

 substance, being derived from anthracene, was named anthrapurpurin ; unlike its 

 isomer pm-purin, however, it is of great value as a coloming-matter. I do not 

 think I shall be going beyond the results of experience if I say it is of as great 

 importance as alizarin itself; with alumina mordants it produces reds of a more 

 scarlet or fiery red than those from alizarin. In fact so fine are the colours 

 produced that, with ordinary alumina-mordants on unoiled cotton, it gives results 

 nearly equal in brilliancy to Tm-key-red produced with madder or garancine ; and 

 I believe the rapid success of artificial alizarin was gi-eatlj^ due to its presence. 

 Most of that consumed at first was for Turkey-red dyeing ; and the coloiu'S were so 

 clear that it was mostly used in combination with madder or garancine, to brighten 

 up the colom-s produced b}' these natural products. 



The pm-ple colours anthrapiu'purin produces with iron mordants are bluer in 

 shade than those of alizai-in, and the blacks are very intense. Its application is 

 practically the same as alizarin, so that they can be used in combination. 



As already noticed, the commercial product called "artificial alizarin " first 

 supplied to the consumer was always a mixture of alizarin and anthrapurpurin ; 

 and various mixtures of these two colouring-matters are still sent into the market ; 

 but, owing to the investigations that have been made and the study and attention 

 that has been given to it by manufacturers, nearly pure alizarin and an thi-a purpurin 

 are also sent into the market— the first being known as " blue-shade alizarin," and 

 the second as red or " scarlet alizarin." 



1876. 5 



