CARBON, a non-metallic element, exist ing in nature in large quantities, both in the free and combined states. It exhibits marked allotropy, at least three distinctly different forms of it being known. These are (1) amorphous carbon; (2) graphite; and (3) diamond. Amorphous carbon is formed when wood or coal or almost any vegetable matter is heated strongly, out of contact with the air, and is familiar to everybody as charcoal, coke and lampblack. Graphite (q.v.) occurs native, and may also be artificially prepared in various ways. Diamond (q.v.), which is crystallized carbon, also occurs native in certain regions, and pure specimens that are devoid of color, or which have certain special tints, are highly esteemed as gems.
Carbon has the chemical symbol C, and an atomic weight of 12.005 if 0=16, and 11.91 if H=1. The specific gravity of diamond is i 3.51, that of graphite is from 2.11 to 2.26 and that of hard gas-coke is about 2.35. The linear coefficient of expansion of diamond (Fahren heit scale) is 0.00000066 at ordinary tem peratures, and that of graphite is 0.0000044. Graphite has an electrical conductivity of about one-twelfth of that of mercury, and hard gas coke, about one one-hundredth. Diamond is practically a non-conductor. The specific heats of diamond and graphite are quite different at ordinary temperatures. Thus at 50° F. dia mond has a specific heat of 0.113, graphite
0.160 and wood charcoal about 0.165. These values increase as the temperature rises, and at about 1100° F. all three varieties have a com mon specific heat of about 0.44.
Carbon is infusible, and insoluble in any known liquid at ordinary temperatures. It dis solves to a limited extent in melted cast iron, and in melted platinum it dissolves freely, separating out again in the form of graphite upon cooling. It is unaltered by the action of acids, except when some powerful oxidizing agent like chlorate of potassium or bichromate of potassium is also present. Chemically it is tetravalent in nearly all of its compounds. It combines with oxygen in three different pro portions, with the formation of a monpxide CO, a dioxide CO: and a suboxide GO.. It also forms, with hydrogen, a great number of compounds known as hydrocarbons (q.v.) ' • and it combines with many of the metals to form carbides (q.v.). With hydrogen, oxygen, nitro gen and small quantities of other elements, it constitutes the entire substance of animals and plants; and the coal beds upon which our modern civilization is founded are composed of vegetable remains from which the elements other than carbon have been mostly expelled by the combined action of heat and pressure.
See AROMATIC COMPOUNDS; CARBON COM