250 SCIENCE PROGRESS 



latter with bromine, so producing dibromanthraquinone and 

 fusing the latter with alkali to produce alizarine. 



C U H 10 -» C M H 8 2 -> C u H 6 2 Br 2 -> C 14 H 6 2 (OH) 2 



Anthracene. Anthraquinone. Dibromanthraquinone. Alizarine. 



The process was patented in 1868, but owing to the pro- 

 hibitive cost of bromine was of no commercial value. 



The process was nevertheless of the greatest importance 

 as showing for the first time the possibility of synthesing pro- 

 ducts on a large scale in the chemical factory which had been 

 hitherto solely of natural origin. 



To obviate the difficulty with regard to the cost of the 

 bromine, the idea occurred simultaneously to Caro in Germany 

 and to Perkin in England to utilise the cheaper sulphuric 

 acid instead, and to fuse the resultant sulphonic acid with 

 alkali. 



But the process was not so simple as it looked, and Caro is 

 said almost to have given up hope of ever making the sulphonic 

 acid until one day, being called from the laboratory for some 

 time and omitting to remove the flame from under the porcelain 

 basin in which the anthraquinone and sulphuric acid were 

 being heated, on his return he found the laboratory filled with 

 fumes of acid, and on examining the basin a distinct pink colour 

 was to be seen on its edges, suggesting to Caro that perhaps 

 the desired reaction had taken place, and that the resultant 

 product had formed the coloured aluminium lake under the 

 influence of the alkali and the alumina of the porcelain. 



A little investigation showed that this was so, and further 

 experiments proved that it was necessary to use fuming 

 sulphuric acid for the sulphonation. 



Perkin had independently arrived at the same conclusion, 

 and the two patents were issued from the British Patent Office, 

 within twenty-four hours of one another, that of Caro, Graebe, 

 and Liebermann bearing the date June 25, 1869, that of Perkin 

 being June 26, 1869. Perkin at once began the production of 

 synthetic alizarine at the Greenford Green works, partly by 

 the sulphuric acid process, and partly by another method which 

 he had patented, starting from dichlor-anthracene, which 

 avoided the use of fuming sulphuric acid, which in those days 

 had to be imported from Germany and was a relatively expen- 



