MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 439 
using the first proportion, part of the bitter taste of the extract remains, showing that 
the rubian is in excess. The liquid being well stirred with the charcoal, the latter 
is allowed to settle, which it does in a very short time, and the liquid, which still re- 
tains a brown colour, is decanted. The charcoal is then placed on a piece of calico 
or on a paper filter and washed with cold water, until the percolating liquid, when 
mixed with muriatic acid and boiled, no longer acquires a green colour, which is a 
sign that the chlorogenine is removed. These operations occupy a very short time, 
in consequence of the rapidity with which the animal charcoal may be washed. The 
animal charcoal is now treated with boiling alcohol, which is filtered boiling hot, and 
the treatment is repeated until it no longer communicates to the alcohol any yellow 
colour. The rubian obtained by evaporating the alcoholic liquid is however impure ; 
it contains a considerable quantity of chlorogenine, however carefully the charcoal 
may have been washed with water, and consequently gives a green powder when 
treated with boiling sulphuric or muriatic acid. This proceeds from the circumstance 
that fresh animal charcoal, when used in the preparation of rubian, invariably takes 
up, besides rubian, a quantity of chlorogenine, which is not removable by cold water, 
but w^hich afterwards dissolves together with the rubian in boiling alcohol. Never- 
theless, on using the charcoal which has been once employed, after treatment with 
alcohol, a second time for the same purpose, it seems to take up rubian alone and no 
chlorogenine, notwithstanding its being, as might be supposed, in the same condition 
for again absorbing the latter as it was in the first instance. At all events, the alcohol 
dissolves only rubian out of the charcoal, when it is used a second time ; and if the 
alcohol should still contain chlorogenine, there will certainly not be a trace of the 
latter in the alcoholic solution, when the charcoal is used for the third time. That 
the attraction of the charcoal for rubian is not diminished after it has been once used 
and then exhausted with alcohol, however indifferent it then becomes towards chloro- 
genine, is proved by the fact that far more rubian is obtained when the charcoal is 
employed for the second time than in the first instance. If the animal charcoal, after 
being once used and exhausted, be heated red-hot so as to destroy all organic matter 
contained in it, it again behaves towards the two substances in the same manner as 
in the first instance, that is, it absorbs a mixture of rubian and chlorogenine. It is 
therefore advisable to reject the rubian which is obtained from the charcoal that has 
been used for the first time*. If a small portion of the alcohol with which the char- 
coal has been treated no longer gives a green colour when mixed with acid and 
boiled, but remains of a pure yellow, it is distilled or evaporated. During evapora- 
tion a small quantity of a dark brown flocculent substance is deposited, which is 
separated by filtration. The solution now contains, besides rubian, another sub- 
stance in small quantity, which is a product of decomposition of rubian itself, and is 
* This impure rubian cannot be purified by means of basic acetate of lead, since when rubian is present in a 
solution together with chlorogenine, the latter is, though not entirely, still in great part precipitated together 
with the rubian by that salt. 
3 L 2 
