CARBIDE, in chemistry, a compound of carbon with another element. The introduction of the electric furnace into practical chemistry was followed by the preparation of many metallic carbides previously unknown, some of which, especially calcium carbide, are now of great commercial importance. Carbides of the following general formulae have been obtained by H. Moissan (M denotes an atom of metal and C of carbon):—
M3C = manganese, iron; M2C = molybdenum; M3C2 = chromium; MC = zirconium; M4C3 = beryllium, aluminium; M2C3 = uranium; MC2 = barium, calcium, strontium, lithium, thorium, &c.; MC4 = chromium.
The principal methods for the preparation of carbides may be classified as follows:—(1) direct union at a high temperature, e.g. lithium, iron, chromium, tungsten, &c.; (2) by the reduction of oxides with carbon at high temperatures, e.g. calcium, barium, strontium, manganese, chromium, &c.; (3) by the reduction of carbonates with magnesium in the presence of carbon, e.g. calcium, lithium; (4) by the action of metals on acetylene or metallic derivatives of acetylene, e.g., sodium, potassium. The metallic carbides are crystalline solids, the greater number being decomposed by water into a metallic hydrate and a hydrocarbon; sometimes hydrogen is also evolved. Calcium carbide owes its industrial importance to its decomposition into acetylene; lithium carbide behaves similarly. Methane is yielded by aluminium and beryllium carbides, and, mixed with hydrogen, by manganese carbide. The important carbides are mentioned in the separate articles on the various metals. The commercial aspect of calcium carbide is treated in the article [Acetylene].
CARBINE (Fr. carabine, Ger. Karabiner), a word which came into use towards the end of the 16th century to denote a form of small fire-arm, shorter than the musket and chiefly used by mounted men. It has retained this significance, through all subsequent modifications of small-arm design, to the present day, and is now as a rule a shortened and otherwise slightly modified form of the ordinary rifle (q.v.).
CARBO, the name of a Roman plebeian family of the gens Papiria. The following are the most important members in Roman history:—
1. Gaius Papirius Carbo, statesman and orator. He was associated with C. Gracchus in carrying out the provisions of the agrarian law of Tiberius Gracchus (see [Gracchus]). When tribune of the people (131 b.c.) he carried a law extending voting by ballot to the enactment and repeal of laws; another proposal, that the tribunes should be allowed to become candidates for the same office in the year immediately following, was defeated by the younger Scipio Africanus. Carbo was suspected of having been concerned in the sudden death of Scipio (129), if not his actual murderer. He subsequently went over to the optimates, and (when consul in 120) successfully defended Lucius Opimius, the murderer of Gaius Gracchus, when he was impeached for the murder of citizens without a trial, and even went so far as to say that Gracchus had been justly slain. But the optimates did not trust Carbo. He was impeached by Licinius Crassus on a similar charge, and, feeling that he had nothing to hope for from the optimates and that his condemnation was certain, he committed suicide.