218 Dr. Schunck on Rubian and its Products of Decomposition. 



of xanthine. The xanthine of most other chemists is however 

 a mixture of rubian with this substance, and possesses therefore 

 the bitter taste of the former, while showing the characteristic 

 behaviour of the latter towards acids. To avoid confusion, I 

 shall no longer employ the name of xanthine, and 1 shall call 

 the substance which gives the green powder with acids Chloro- 

 genine. Now these two substances, though of very different 

 nature, behave similarly towards many reagents. If, for instance, 

 basic acetate of lead be added to a watery extract of madder, 

 according to the method proposed by Berzelius for the pre- 

 paration of xanthine, and adopted with a slight modification by 

 Mr. Higgin, there is produced a red precipitate, which after 

 being washed and decomposed with sulphuretted hydrogen or 

 sulphuric acid, gives a solution containing rubian; but the 

 presence of chlorogenine is also indicated by its turning dark 

 green when boiled with the addition of sulphuric or muriatic 

 acid. Hence it follows that chlorogenine, though it is not 

 thrown down by basic acetate of lead, when present alone in 

 a solution, is still in part precipitated thereby when rubian is 

 present at the same time. The same circumstance takes place 

 with other preeipitants. 



After numerous experiments I discovered a property of rubian, 

 which is perhaps more characteristic of it than any other, and 

 that is the remarkable attraction which is manifested by it 

 towards all substances of a porous or finely-divided nature, and 

 it was this property by means of which I was at length enabled 

 to obtain it in a state of purity. If to a watery extract of mad- 

 der a quantity of protochloride of tin be added, a light purple 

 lake is precipitated. Most of the rubian remains in the solution, 

 which still retains its yellow colour and bitter taste. If, however, 

 after filtering, sulphuretted hydrogen be passed through it, then, 

 provided the quantity of tin still in solution be sufficiently large, 

 the sulphuret of tin, at the moment of precipitation, carries down 

 the whole of the rubian, and the solution loses its bitter taste 

 and the greater part of its yellow colour. The whole of the 

 chlorogenine remains in solution, and may easily be detected 

 in the filtered liquid by means of acids. If the sulphuret of 

 tin, after being collected on a filter and well washed with cold 

 water until the percolating liquid no longer gives a green colour 

 on being mixed with acid and boiled, be treated with boiling 

 alcohol, a yellow solution is obtained, which on evaporation gives 

 pure rubian, without any admixture of chlorogenine, in the 

 shape of a dark yellow, brittle substance. The same effect is 

 produced by sulphuret of lead. If sugar of lead be added to 

 an extract of madder, a dark reddish-brown precipitate falls, the 

 liquid still containing the rubian of the extract, as seen by its 



