414 Progress of Foreign Science, 



Chapter III. On the Mode of A ction of Charcoal in discolouring. 



It is generally thought that the charcoal acts on co- 

 louring matters, by decomposing them ; and this opinion is 

 founded on it having been observed, in treating different matters 

 with charcoal, such as beer, mucilage, melasses, wine, Sfc, 

 that the discoloration was accompanied with a disengagement 

 of gas. Presuming that this opinion v/as entirely erroneous, 

 and that to thedecomposition of the colouring matter, a disen- 

 gagement of gas had been improperly ascribed, which must 

 depend on some other cause, M. Bussy made the following ex- 

 periments : He took 8 ounces of melasses, which he diluted 

 with a pound and a half of distilled water, agitated it with carbon- 

 ate of lime to neutralize the acids which might act on the char- 

 coal ; then filtered the liquid, and heated it to expel the gases 

 which might be held in solution in the water. 



On the other hand, he took 1 ounce of blood-charcoal very 

 carefully washed ; boiled it in 8 ounces of water, to expel all 

 the air which might be adhering to it, and when he judged it 

 to contain no more air, he added the melasses, so that the 

 vessel which he employed, was perfectly full. The apparatus 

 being thus arranged, and perfectly freed from air, he engaged 

 the extremity of the tube, under a graduated tube filled with 

 water ; and he heated the vessel in the salt-Avater bath for two 

 hours, at a temperature approaching to that of boiling water. 

 No gas whatever was disengaged, and the liquor became com- 

 pletely colourless ; the experiment succeeds equally well in the 

 cold. He tried also cochineal, and several other colouring 

 matters, and he obtained no evolution of gas. As to wine, we 

 must take great care to employ a charcoal which has been pre- 

 viously treated with muriatic acid, for otherwise, the acids 

 which it contains, decompose the carbonate of lime which is 

 present in the charcoal, and gives rise to a disengagement 

 of gas. 



The colouring matters not beingdecomposedby the charcoal, as 

 appears from this experiment, we conceive they must fix them- 

 selves in the charcoal, augment its weight proportionally to the 

 quantity of liquor discoloured ; and that, in some circumstances, 

 we may re-produce the solution of the colouring matter. 



To verify this conjecture, he took three species of charcoal, 

 which he knew acted with a different intensity ; these were : 

 1st, charcoal of blood; 2d, bone-black, purified; 3d, crude 

 bone-black. These charcoals after having been washed with 

 boiling water, to separate all their soluble ingredients, were 

 dried at the water-bath, for the same space of time. He then 

 took 5 grammes- of each of these charcoals, which he heated 

 separately with 20 grammes of melasses, diluted with 4 parts 

 of water. This liquor was left in contact with each of the char- 

 coals during the same time ; at the end of which they were fil- 



