48 



CARBON. 



once between die diamond and charcoal, m their ex- 

 ternal properties, we are forced to believe that they 

 are identically of the same nature. The diamond is, 

 therefore, pure carbon, and differs from charcoal 

 (leaving out of question its trifling impurities) only in 

 the arrangement of its molecules. 



The substance in which carbon exists next in pu- 

 rity is charcoal. For common purposes tins is pre- 

 pared by piling billets of wood in a pyramidical form, 

 with vacuities uetween them for the admission of air, 

 mrriug them with earth, and inflaming them. In 

 consequence of the heat, part of the conibustible sub- 

 stance is consumed, part is volatilized, together with 

 a j in ii H i of water, and there remains behind the lig- 

 neous fibre only of the wood, in tin- form of a black, 

 brittle, and porous body. When required pure, and 

 in small quantities, for the purposes of the chemist, 

 it may be obtained by immersing the wood in sand 

 contained in a crucible exposed to heat. According 

 to the experiments of Messrs Allen and Pepys, the 

 wright of cliarcoal obtained from 100 parts of differ- 

 ent woods was as follows : fir, 18-17 ; lignum vita3, 

 17-25; box, 20-25; beech, 15; oak, 17-40; maho- 

 gany, 15-75. 



Lampblack is charcoal ID a state of minute division, 

 and is prepared for the demands of trade from the 

 dregs which remain after the eliquation of pitch, or 

 else from small pieces of fir-wood, winch are burned 

 in furnaces of a peculiar construction, the smoke of 

 which is made to pass through a long horizontal flue, 

 terminating in a close, boarded chamber. The roof 

 of this chamber is made of coarse cloth, through 

 which the current of air escapes, while the soot, or 

 lampblack, remains behind. Coke is a peculiar kind 

 of charcoal, which remains in the retort, after the 

 heating of coal to procure the coal gas. 



Ivory-black, or animal charcoal, is obtained from 

 bones made red-hot in a covered crucible, and con- 

 sists of cliarcoal mixed with the earthy matters of the 

 Ixme. 



Wood charcoal, well prepared, is of a deep-black 

 colour, brittle and porous, tasteless and inodorous. 

 It is infusible in any heat a furnace can raise ; but, 

 by the intense heat of a powerful galvanic apparatus, 

 it is hardened, and at length is volatilized, presenting 

 a surface with a distinct appearance of having under- 

 gone fusion. The density of charcoal, according to 

 Mr Leslie, is little short of that of the diamond itself, 

 although its specific gravity has usually been consi- 

 dered as low as 2-00. Charcoal is insoluble in water, 

 and is not affected by it at low temperatures ; hence 

 wooden stakes, which are to be immersed in water, 

 are often charred to preserve them. 



Owing to its peculiarly porous texture, charcoal 

 possesses the property of absorbing a large quantity 

 of air, or other gases, at common temperatures, and 

 of yielding the greater part of them when heated. It 

 appears, from the researches of Saussure, that differ- 

 ent gases are absorbed by it in different proportions. 

 He found that charcoal prepared from box-wood ab- 

 sorbs, during the space of twenty-four or thirty-six 

 hours, of 



Ammoniacal gag 

 Muriatic acid, 

 Carbonic acid, 

 Oxygen, . . 

 Hydrogeu, 



90 times its volume : 



85 



35 

 9-25 

 1-75 



do. 

 do. 

 do. 

 do. 



Cliarcoal likewise absorbs the odoriferous and col- 

 ouring principles of most animal and vegetable sub- 

 stances. Thus, all saline substances, which, from 

 the adherence of vegetable or animal extractive mat- 

 ter, are of a brown colour, as crude tartar, crude 

 nitre, impure carbonate of ammonia, and other salts, 

 may, after being digested through the medium of 

 water with charcoal be obtained white by a second 



crystallization. Resins, gum-resins, assafoetida, opi- 

 um, balsams, essential oils, and many other substan- 

 ces, even those that liave the strongest smell, are 

 rendered nearly inodorous when they are rubbed with 

 charcoal and water, or when solutions of them in 

 alcohol are macerated with the cliarcoal, or filtrated 

 repeatedly through it. A number of the vegetable 

 tinctures and infusions also lose their colour, smell , 

 and much of then- taste, by the same process. Com- 

 mon vinegar, on being boiled with charcoal powder, 

 becomes colourless. Malt spirit, by distillation with 

 cliarcoal, is freed from its disagreeable flavour. In 

 the same manner wines, also, become colourless, and 

 distilled waters lose their odours. Water, which, 

 from having been long kept in wooden vessels, as 

 during long voyages, has acquired an offensive smell, 

 is deprivea of it by filtration through charcoal pow- 

 der, or even by agitation with it for a few minutes, 

 especially when a few drops of sulphuric acid have 

 also been added. Hence, also, it lias been found 

 that, by charring the inside of casks for keeping wa- 

 ter, it may be preserved a Jong time without spoiling. 

 Cliarcoal can even remove or prevent the putres- 

 cence of animal matter. If a piece of flesh lias be- 

 come tainted, the taste and smell may, in a great 

 measure, be removed, by rubbing it with charcoal 

 powder ; and it may be preserved fresh for some 

 time by burying it in the same substance. To pro- 

 duce these effects, however, it is necessary that the 

 charcoal should have been well calcined and newly 

 prepared. 



The uses of charcoal are extensive. It is used as 

 fuel in various arts, where a strong heat is required 

 without smoke, as in dyeing, and in various metal- 

 lurgic operations. By cementation with charcoal, 

 iron is converted into steel. It is used in the manu 

 facture of gunpowder, in its finer state of aggrega- 

 tion, under the form of ivory-black, lamp-black, &c. 

 It is the basis of black paint ; and, mixed with fat 

 oils and resinous matter, to give a due consistence, 

 it forms the composition of printing ink. It is used 

 to destroy colour and odour, particularly in sirups ; 

 to purify honey; to resist putrefaction; to confine 

 heat, and for a number of other important purposes. 



When cliarcoal is heated to a certain degree in 

 the open air, or in oxygen gas, it takes fire, and 

 burns with the production of an elastic vapour, which 

 has been called carbonic acid gas. It is usually ob- 

 tained, however, by other processes. It exists, 

 combined with lime, in the different varieties of 

 limestone, marble, and chalk ; and, if any of these 

 substances be exposed to a strong heat, the affinity 

 of the acid to the lime is so far weakened, that it 

 assumes the elastic form, ana may be collected. An 

 easier mode is also practised for effecting its dis- 

 union, through the affusion of one of the more 

 powerful acids. 



From the experiment of the direct formation of 

 this acid, by the combustion of charcoal in oxygen 

 gas, its composition has been determined to be 27-4 

 carbon and 72-6 oxygen. Tennant illustrated its 

 nature analytically, by passing the vapour of phos- 

 phorus over chalk, or the carbonate of lime, heated 

 to redness in a glass tube. The phosphorus took 

 oxygen from the carbonic acid, charcoal, in the form 

 of a light, black powder, was deposited, and the 

 phosphoric acid, which was formed, united with the 

 lime. 



Carbonic acid is a colourless, inodorous, elastic 

 fluid, which possesses all the physical properties of 

 the gases in an eminent degree, and requires a pres- 

 sure of thirty-six atmospheres to condense it into a 

 liquid. Its specific gravity, compared with common 

 air, is 1-5277. It extinguishes burning substances 

 of all kinds, and is incapable of supporting the re- 



