TRANSACTIONS OF THE SECTIONS. 61 



portant colouring-matter in madder, purpurin, which so pertinaciously follows ali- 

 zarin, is in constitution very nearly allied to it, and is also an anthracene derivative. 

 Scientifically, then, the artificial production of this natural product was complete ; 

 but the practical question, Can it he made in the laboratory cheaper than it can he 

 obtained from the root ? had yet to be dealt with. The raw material, the anthracene, 

 a by-product in the manufacture of coal-gas, had as yet only been obtained as a 

 chemical curiosity ; it had no market value ; its cost would depend on the labour 

 of separating it from the tar and the amount obtainable. But with regard to the 

 bromine necessary to form the bibromanthraquinone it was different ; the use of 

 such an expensive reagent would preclude the process becoming a manufacturing 

 one. But could no cheaper reagent be used in place of the bromine, and thus crown 

 this discovery by utilizing it as a manufacturing process ? It was our countryman 

 Mr. Perkin who first showed how this could be done, and has since proved the very 

 practical and important nature of his discovery by carrying it out on the manufac- 

 turing scale. The nature of Perkin's discovery was the forming, in place of a 

 bibromanthraquinone, a disulphoanthraquinone ; in a word, he used sulphuric acid in 

 place of bromine, obtaining thus a sulpho-acid in place of a bromine substitution- 

 compound. The property of these sulpho-acids, containing the monovalent group 

 H SO3, which is the equivalent to the atom of bromine, is that on being boiled with 

 an alkali they are decomposed, and a con-esponding alkaline salt formed. Thus the 

 change from the anthraquiuone to the alizarin was effected by boiling it with sul- 

 phuric acid. At a high temperature it dissolves, becoming a sulpho-acid, 



Ci4 Hj < H SO3 ; and then the further changes follow, as they did with the bromine 



(HSO., 

 compound. The sulpho-acid boiled with potash is decomposed, and a potash salt 

 of alizarin and potassic sulphite are formed ; acid then precipitates the alizarin 

 as a bright yellow substance. 



While Perkin was carrying on these researches in this country, Caro, Graebe, and 

 Liebermann were carrying on somewhat similar ones in Germany ; and in both 

 countries have the scientific experiments developed into manufacturing industries. 

 My knowledge extends only to the English manufactory ; and if any excuse be ne- 

 cessary for having asked your attention to-day to this long history of a single sub- 

 stance, I think I must plead the existence of that manufactory as my excuse ; for 

 it is not often that purely scientific research so rapidly culminates in great practical 

 undertakings. Already has the artificial become a most formidable opponent to the 

 natural product ; and in this struggle, already begun, there can be no doubt which 

 will come off victorious. 



In the manufactory is rigidly carried out the exact process I have already 

 described to you. In tar there is about one per cent, of anthracene ; this, in a 

 crude impure state, is obtained from it by the tar-distiller and sent by him to 

 the colour-works. Here it is purified by pressure, by dissolving from it many of 

 its impurities, and, lastly, by volatilizing it. Then comes the conversion of it into 

 the anthraquinone by oxidizing agents, nitric or chromic acid being used, then the 

 formation of the sulpho-compound by heating it with sulphuric acid to a tempera- 

 ture of about 260° C. The excess of acid present is then neutralized by the addi- 

 tion of lime, and the insoluble calcic sulphate is filtered off. To the filtered liquid 

 sodic carbonate is added, and thus the calcic salt of the sulpho-acid is changed into 



( (0,)" 

 the sodic salt, CioHg •^NaS03. This is afterwards heated to about 180° 0. with 



(NaS03 

 caustic soda,' thus decomposing the sulpho-acid and forming the soda salt of 

 alizarin and the sodic sulphite. The alizarin salt so formed remains in solution, 

 giving to the liquid a beautiful violet colour. From this solution sulphuric acid 

 precipitates the alizarin as an orange-yellow substance. It is allowed to settle in 

 large tanks, and then is run, in the form of a yellowish mud, which contains either 

 10 or 15 per cent, of dry alizarin, into barrels, and is in this form sent to the 

 print-works, and used much in the same way as the original ground madder 

 was used. 



This alizarin mud, as I have called it, containing but 10 per cent, of dry alizarin, 



