or 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