CARBON, in chemistry. The term car bon having been understood in different senses, and having been actually applied to different substances, it is necessary to guard against the ambiguity arising from this circumstance, and with this view to trace in a general manner the progress of those discoveries, from which the name originated, and by which its application has since been changed.
When vegetable matter, especially the more solid parts of plants, the wood for example, is exposed to heat in close ves sels, it is decomposed ; the more volatile principles are disengaged, and there re mains a black, shining, porous body, com posed of the various substances which are not convertible by a high temperature to the gaseous form. This substance is termed charcoal. While the atmospheric air is excluded, it is neither fused nor volatilised by any increase of heat ; but when the air is admitted, it suffers combustion, and it continues to burn till nearly the whole of it is consumed ; the residuum amounting to not more than the 200th part of the weight of the original charcoal. This residuum is un inflammable, and consists principally of saline and metallic matter. Charcoal then is a heterogeneous substance. By far the greater part of it consists of an inflammable substance, which combines with oxygen, and forms the carbonic acid of the modern nomenclature. But this in flammable matter, as it exists in the char coal, is mixed or combined with the saline and metallic substances left after its combustion. For the sake of pre cision, a distinction is made in the new nomenclature, between the pure inflam. mable base and the substance in which it is thus presented to us. Charcoal is that black porous substance obtained from vegetable matter, especially from wood, by exposing it to heat; and the pure inflammable substance, which com. poses by far the greater part of the char coal, was termed carbon. Carbon, there fore, according to this signification, was charcoal destitute of the small quantity of saline and metallic matter usually mixed with it. The principal advantage of the introduction of the name carbon was, not merely that of distinguishing the inflam mable base from the substance in which it was mixed with other ingredients, but also that of giving a term capable of com bination, and of affording those deriva tive appellations which the modern sys tem requires. This s';bstance is not a hy
pothetical being, since, by certain chemi cal processes, by the decomposition of carbonic acid for instance, or of alcohol by heat, it is possible to obtain it perfect ly pure. It exists in a large quantity as a component part of vegetable sub stances; it enters into the composition of animal matter, and is contained in sub stances belonging to the mineral king dom. This substance, which, when it is obtained pure, exists in the form of a ve ry light black powder, was, until within these few years, considered as a simple body; but experiments have proved, that it is a compound, containing an in flammable substance, according to some chemists, in a state of imperfect oxyda tion ; according to others, combined with hydrogen. It had been known for a con siderable time, that the diamond, the most beautiful and most unchangeable of the productions of nature, is combustible, or that when heated o ith oxygen gas it suffers combustion. Lavoisier made some experiments to ascertain the nature of the product of this combustion ; and he found it to be an acid precisely the same with that which is produced by the burn. ing of charcoal—what is termed the car bonic acid. He did not, however, as certain the proportion of it with suffi cient accuracy to draw any precise conclu sion. Some time after, Mr. Tennant re peated the experiment of oxydizing the diamond, by exposing it to heat along with nitrate of potash in a gold tube. He also found that carbonic acid was formed ; and from an experiment on a small scale, it appeared that about the same quantity of carbonic acid was af forded by the oxygenation of the diamond, as would have been produced by the combustion of the same weight of char coal. He concluded that the diamond was carbon, and differed from charcoal prin cipally in its form and state of aggrega tion ; that, in short, it might be consider ed as carbon crystallized.