Dr. Schunck on Rubian and its Products of Decomposition. 221 



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 re- 

 movable by cold water, but which afterwards dissolves together 

 with the rubian in boiling alcohol. Nevertheless, 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 al- 

 cohol dissolves only rubian out of the charcoal, when it is used 

 a second time ; and if the alcohol should still contain chloro- 

 genine, 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 chlorogenine, 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 charcoal 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 evaporation a small quantity of 

 a dark brown fiocculent substance is deposited, which is separated 

 by filtration. The solution now contains, besides rubian, another 

 substance in small quantity, which is a product of decomposi- 

 tion of rubian itself, and is probably formed by the application 

 of too great a heat in the process of drying the madder. There 

 an: two ways in which this substance may be removed. The 

 first consists in adding to the solution sugar of lead, which pre- 

 cipitates it in dark reddish-brown flocks. These being separated 

 by filtration, the rubian is precipitated by means of basic acetate 

 of had, and the light red compound or lake, after being washed 

 with alcohol to remove all excess of lead salt, is decomposed 

 either with sulphuretted hydrogen, or better still with sulphuric 

 acid, the excess of the latter being removed by carbonate of lead. 



* This impure rubian cannot be purified by means of basic acetate of 



lead) sinre when rubian is present in si solution together with chlorogenine, 

 the latter is, though not entirely, still in great part precipitated together 

 with the rubian by that salt. 



