Dr. Schimck on Rubian and its Products of Decomposition. 219 



deep yellow colour and bitter taste. If sulphuretted hydrogen 

 be now passed through the filtered liquid, a great part of the 

 rubian goes down with the sulphuret of lead, and may again be 

 separated from it by means of boiling alcohol. That this action 

 of the sulphurets on rubian depends veiy much on their state of 

 division, and is therefore mainly of a mechanical, and not che- 

 mical nature, is proved by the fact, that the sulphurets of tin 

 and lead, if prepared by precipitation from solutions of salts in 

 water, and then allowed to settle and repose for some time before 

 being added to a watery extract of madder, remove far less rubian 

 from it than they do, if they are formed in the extract itself, 

 whence it follows that it is only in the minute state of division, 

 in which they exist at the moment of precipitation, before the 

 particles have time to cohere, that these sulphurets exert any 

 great attraction for rubian. That they do however combine 

 with some portion of the rubian, is proved by the fact, that the 

 power of dyeing in an extract of madder is very much diminished 

 by adding to it sulphuret of tin or lead, previously precipitated. 

 Of the two sulphurets, the sulphuret of tin, which is always 

 precipitated in much finer particles than the other, is by far the 

 most powerful absorbent of rubian. If equivalent quantities of 

 protochloride of tin and acetate of lead be added to equal measures 

 of watery extract of madder, the sulphuret of tin from the former 

 absorbs at least twice as much rubian as the sulphuret of lead 

 from the latter. Sulphuret of copper acts differently. If sul- 

 phate of copper be added to the extract of madder, a precipitate 

 is produced, as in the case of almost all metallic salts. On pass- 

 ing sulphuretted hydrogen through the filtered liquid, the latter 

 becomes dark brown, but no sulphuret of copper is precipitated. 

 . This attraction of surface exerted towards rubian by bodies in 

 a state of minute division is not confined to metallic sulphurets. 

 There are few bodies which exceed animal charcoal in porosity, 

 or which, in other words, possess for the same bulk a greater 

 extent of surface. I found accordingly that animal charcoal ex- 

 hibits a still greater attraction for rubian than even sulphuret of 

 tin. A very small quantity of animal charcoal is sufficient to 

 deprive an aqueous extract of madder of its bitter taste and of 

 its tinctorial power. Lamp-black acts in the same manner, 

 though much less powerfully. Wood charcoal however has no 

 absorbent effect whatever on rubian. All these substances at- 

 tract rubian alone, leaving the other substances contained in 

 the extinct, such aa cblorogenine, sugar and pectine, untouched. 

 Bf means of boiling alcohol part of the rubian in combination 

 with them it again removed, and thus an easy and efficient means 

 is given of obtaining rubian in a state of purity. Of these sub- 

 stances none is so well adapted in all respects as animal charcoal. 



