27 



February 13, 1851. 



SIR BENJAMIN C. BRODIE, Bart, V.P., in the Chair. 



A paper was read, entitled, "On Rubian and its Products of 

 Decomposition." By Edward Schunck, Esq., F.R.S. Received 

 January 9, 1851. 



After adverting to the obscurity in which the inquiry concerning 

 the state in which the colouring matter of Madder originally exists 

 in this root is involved, the author refers to the change which takes 

 place in the root, especially if in a state of powder, during the lapse 

 of time, and to the little light which has been thrown by chemical 

 investigations on the nature of the process by which the change is 

 effected. He states that it has been suspected by several chemists 

 that there exists originally some substance in madder, which, by 

 the action of fermentation, or oxidation, is decomposed, and gives 

 rise by its decomposition to the various substances endowed either 

 with a red or yellow colour, which have been discovered during the 

 chemical investigations of this root. In his papers on the colouring 

 matter of madder, he has described four substances derived from 

 madder, only one of which is a true colouring matter, but all of 

 them capable under certain circumstances, as for instance in com- 

 bination with alkalies, of developing red or purple colours of various 

 intensity. After referring to the opinions of M. Persoz and the in- 

 vestigations of Mr. Higgin relative to xanthine and alizarine, the 

 author observes that, by adding a variety of substances to an extract 

 of madder with cold water, he was enabled to ascertain under what 

 circumstances and by what means the tinctorial power of the liquid 

 is destroyed, and consequently what is the general character of the 

 substance or substances to which it is due. He found that by adding 

 sulphuric, or muriatic acid to the extract, and heating, the liquid, 

 after neutralization of the acid, was no longer capable of dyeing. 

 The tinctorial power was also destroyed by the addition of hydrate 

 of alumina, magnesia, protoxide of tin, and various metallic oxides, 

 but not by carbonate of lime, or carbonate of lead. In all cases in 

 which the property of dyeing in the extract was destroyed, he inva- 

 riably found that its bitter taste and bright yellow colour were de- 

 stroyed. Having shown, in his former papers on this subject, that 

 the intensely bitter taste of madder and its extracts is due to a pe- 

 culiar substance to which he has given the name of rubian ; and as 

 it appeared from these preliminary experiments that this substance, 

 though itself no colouring matter, is in some way concerned in the 

 changes whereby a formation of colouring matter is induced in 

 aqueous extracts of madder, he proposed to himself to examine its 

 properties and products of decomposition more in detail than he had 

 hitherto done. 



After numerous experiments, undertaken with the view of ob- 

 taining pure rubian in quantities sufficiently large for the purposes 

 of examination, he discovered a property of that substance, by which 

 he was enabled to obtain it in a state of purity, namely the remark- 



