TRANSACTIONS OF THE SECTIONS. 49 



the practical working of the memorable discovery of the production of artificial 

 alizarine, the colom-ing-matter of madder, by MM. Graebe and Liebermann. This 

 discovery, announced at our last Meeting, is of the highest importance, whether we 

 regard its scientific interest or its practical and commercial value ; and it ditters 

 from all the former results which have been brought about by the application of 

 science to the production of colouring-matters, inasmuch as this has reference to 

 the artificial production of a natural vegetable colouring substance which has been 

 used as a dye from time immemorial, and which is still employed in enormous 

 quantities for the production of the pink, purple, and black coloiu's which are seen 

 everywhere on prmted calicoes. 



During the past year much progress has been made in the practical working of 

 the processes by which this colouring-matter is obtained from the hydrocarbon 

 anthracene contained in coal-tar ; and new and more economical plans for eflecting 

 the transformation have been independently proposed by Perkin and Caro, and 

 Schorlemmer and Dale. The theoretical investigation of the reaction, and especially 

 of the nature of some other peculiar products in addition to alizarine which render 

 the artificial colouring-matter difl"erent from the natural colour, has been carried 

 out by Mr. Perkin and by Dr. Schunck. As we are promised papers on this subject 

 from both these gentlemen, 1 need not at present enter further into these interesting 

 questions. 



The surest proof of perfection in a manufacture is the degree in which the waste 

 products are utilized, and in which the processes are made continuous. One by 

 one the imperfections of the original discovery are made to disappear, the products 

 which were wasted become sources of profit ; and in many cases their utilization 

 alone renders possible the continuance of the manufacture in the middle of a 

 rapidly increasing district. The Section will have the opportunity of inspecting 

 the practical working of at least two of the most valuable of these new processes. 

 The first of these has been at work for some time ; it is that of the recovery of the 

 sulphur from the vat-waste, that hete noire of the alkali-makers and of their neigh- 

 bours. Dr. Mond has now satisfactorily solved the difiicult problem of economically 

 regaining the sulphur by oxidizing the insoluble monosulphide of calcium to the 

 soluble hyposulphite, and decomposing this by hydrochloric acid, when all the 

 sulphur is deposited as a white powder. 



The second of these discoveries relates to the recovery or regeneration of the 

 black oxide of manganese used for the evolution of chlorine in the manufactiure of 

 bleaching-powder. This subject has long attracted the attention of chemists; and 

 a feasible though somewhat costly process, that of Dunlop, has been at work for 

 some time at Messrs. Tennant's works at St. Rollox. During the last year a very 

 beautifully simple and economical process, proposed by Mr. Weldon, and first 

 successfully carried out on a practical scale in Messrs. Gamble's works at St. 

 Helens, has quickly obtained recognition, and is now worked by more than thirty- 

 seven fijms throughout the kingdom. 



. The principle upon which this process depends was explained by Mr. Weldon at 

 the Exeter Meeting. It depends on the fact that although when alone the lower 

 oxides of manganese cannot be oxidized by air at the ordinary temperature and 

 under the ordinary pressure to the state of dioxide, yet this is possible when one 

 molecule of lime is present to each molecule of the oxide of manganese. The 

 manganous oxide is precipitated from the still-liquors with the above excess of 

 lime ; and by the action of air on this a black powder, consisting of a compound of 

 manganese dioxide and lime, MnOa CaO, or calcium manganite, is formed. This 

 of course is capable of again generating chlorine on addition of hydrochloric acid ; 

 and thus the chlorine process is made continuous, with a working loss of only 2 j per 

 cent, of manganese. The Section will have the advantage of seeing Mond's process 

 at work at Messrs. Hutchinson's, and Weldon's process at Messrs. Gaskell, Deacon 

 and Co.'s at Widnes. 



A third process, which may possibly still further revolutionize the manufacture of 

 bleaching-powder, is the direct production of chlorine from hydrochloric acid with- 

 out the use of manganese at all. In the presence of oxygen and of certain metallic 

 oxides, such as oxide of copper, hydrochloric acid gas parts at a red heat ■\s'ith all 

 its hydrogen, water and chlorine being formed. This interesting reaction is employed 



1870. 4 



