438 MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 
madder, the siilphiiret 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 passing sulphuretted hydrogen through the 
filtered liquid, the latter becomes dark brown, but no sulphuret of copper is pre- 
cipitated. 
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 exhibits 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 attract rubian alone, leaving the other substances contained in 
the extract, such as chlorogenine, sugar and pectine, untouched. By means of boiling 
alcoliol part of the rubian in combination with them is again removed, and thus an 
easy and efficient means is given of obtaining rubian in a state of purity. Of these 
substances none is so well adapted in all respects as animal charcoal. In employing 
sulphuret of tin, which is the only one that at all approaches it in efficiency, much 
time is consumed in the process of filtration and washing. Besides this, I found 
that on operating with it on a large scale, the rubian obtained was in great part de- 
composed on evaporating the alcoholic solution, just as if it contained a quantity of 
acid ; and even on treating a portion of the solution with carbonate of lime, for the 
purpose of neutralizing any free acid that might be present, and evaporating over 
sulphuric acid at the ordinary temperature, there was obtained a deliquescent mass, 
which, as further experiments showed, could not be considered as pure rubian. 
After many trials I at length adopted the following method of preparation, which 
surpasses all others in facility and certainty of execution. 
A weighed quantity of madder* being placed on a piece of calico or fine canvas 
stretched on a wooden frame, boiling water, which is preferable to cold water, as all 
decomposition of the rubian by means of fermentation is thereby arrested, is poured 
on it, four quarts of the latter being sufficient for every pound of madder. A dark 
yellowish-browm liquor is obtained, to which there is added, while hot, for every 
pound of madder taken 1 ounce of animal charcoal, prepared in the usual way from 
bones. This proportion of charcoal should not be exceeded, for if an excess of it be 
taken, as for instance 1^ ounce for every pound of madder, the whole of the rubian 
is certainly removed from the solution ; but on afterwards treating the charcoal with 
alcohol very little rubian is dissolved, from which it appears that the solvent power 
of the alcohol only overcomes the attraction of the charcoal for rubian in part. In 
* Avignon madder, of the variety called Rosa, was the kind used. 
