Mr. Chum on the Manner in which Cotton unites with Colouring Matter. 99 



If we examine, says Professor Mitscherlich, a piece of boxwood by 

 the microscope, we find it composed of cells, which have a diameter 

 of about j<t'^(yth of an inch. Heated to redness, the form of these 

 colls suffers no change, for the particles of which it is composed have 

 no tendency to run together in fusion. A cubic inch of boxwood char- 

 coal, boiled for some time in water, absorbed phs of its volume of that 

 liquid ; from which, and other data, it was computed that the surface 

 of its pores was 73 square feet. 



Saussuro observed, that a cubic inch of boxwood charcoal absorbed 

 35 cubic inches of carbonic acid ; and as the solid part of the charcoal 

 formed Jths of its bulk, these 35 inches of gas must have been con- 

 densed into Jths of an inch ; or 56 cubic inches into one, under the 

 ordinary pressure of the atmosphere. But carbonic acid liquefies 

 under a pressure of 3G-7 atmospheres ; and therefore, with a power of 

 condensation equal to 56 atmospheres, which the charcoal exerted in 

 Saussure's experiment, at least one-third of the gas must have assumed 

 the liquid state within its pores. Every other porous body has the 

 same property as charcoal. Raw silk, linen thread, the dried woods 

 of hazel and mulberry, though they condense but a small quantity of 

 carbonic acid, take up from 70 to 100 times their bulk of ammoniacal 

 gas ; and Saxon hydrophane, which is nearly pure silica, absorbs 64 

 times its bulk. The gases enter into no combination with the solid 

 which absorbs them, for the air pump alone destroys their union. 



The manner in which gases are attracted to the surface of solid 

 bodies is very much like that which these exert on substances dis- 

 solved in water. The charcoal of bones has been long employed to 

 remove colouring matter from the brown solution of tartaric acid; 

 from syrup in the refining of sugar ; and from a variety of other liquids 

 containing organic substances; and it is found that the colouring mat- 

 ter so attracted remains attached to the surface of the charcoal without 

 effecting any change upon it. In this animal charcoal the carbon is 

 mixed with ten times its weight of phosphate of lime, and if that be 

 washed away by an acid, the remaining charcoal has nearly twice tlie 

 discolouring power of an equal weight of ivory black. Bussy, who has 

 made the action of these charcoals the subject of particular investiga- 

 tion, informs us, that if ivory black, after the extraction of its earth 

 of bones by an acid, be calcined along with potash, and the potash be 

 afterwards washed out ; or if blood be at once calcined with carbonate 

 of potash, and washed, the remaining charcoal has the power of dis- 

 colouring twenty times as much vsyrup as could be done by the original 

 bone charcoal. Animal charcoal removes also lime from lime water ; 

 iodine from a solution of iodide of potassium, and metallic oxides from 

 their solution in ammonia and caustic potash. 



A satisfactory explanation of tliese remarkable facts has yet to be 

 sought for. Mitscherlich calls the force which produces them an action 

 of contact, or attraction of surface ; and he calculates, as we have seen, 



