Page:EB1911 - Volume 05.djvu/317

 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.

 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 (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., statesman and orator. He was associated with C. Gracchus in carrying out the provisions of the agrarian law of Tiberius Gracchus (see ). When tribune of the people (131 ) 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.

2. His son,, surnamed Arvina, was a staunch supporter of the aristocracy, and was put to death by the Marian party in 82. He is known chiefly for the law (Plautia Papiria) carried by him and M. Plautius Silvanus when tribunes of the people in 90 (or 89), whereby the Roman franchise was offered to every Italian ally domiciled in Italy at the time when the law was enacted, provided he made application personally within sixty days to the praetor at Rome (see : History, II. “The Republic,” Period C.). The object of the law was to conciliate the states at war with Rome and to secure the loyalty of the federate states. Like his father, Carbo was an orator of distinction.

3. (c. 130–82 ), nephew of (1). He was a strong supporter of the Marian party, and took part in the blockade of Rome (87). In 85 he was chosen by Cinna as his colleague in the consulship, and extensive preparations were made for carrying on war in Greece against Sulla, who had announced his intention of returning to Italy. Cinna and Carbo declared themselves consuls for the following year, and large bodies of troops were transported across the Adriatic; but when Cinna was murdered by his own soldiers, who refused to engage in civil war, Carbo was obliged to bring them back. In 82 Carbo, then consul for the third time with the younger Marius, fought an indecisive engagement with Sulla near Clusium, but was defeated with great loss in an attack on the camp of Sulla’s general, Q. Caecilius Metellus Pius [see under (6)] near Faventia. Although he still had a large army and the Samnites remained faithful to him, Carbo was so disheartened by his failure to relieve Praeneste, where the younger Marius had taken refuge, that he decided to leave Italy. He first fled to Africa, thence to the island of Cossyra (Pentellaria), where he was arrested, taken in chains before Pompey at Lilybaeum and put to death.

 CARBOHYDRATE, in chemistry, the generic name for compounds empirically represented by the formula Cx(H2O)y. They are essentially vegetable products, and include the sugars, starches, gums and s (q.v.).

 CARBOLIC ACID or (hydroxy-benzene), C6H5OH, an acid found in the urine of the herbivorae, and in small quantity in castoreum (F. Wöhler, Ann., 1848, 67, p. 360). Its principal commercial source is the fraction of coal-tar which distils between 150 and 200° C., in which it was discovered in 1834 by F. Runge. In order to obtain the phenol from this distillate, it is treated with caustic soda, which dissolves the phenol and its homologues together with a certain quantity of naphthalene and other hydrocarbons. The solution is diluted with water, and the hydrocarbons are thereby precipitated and separated. The solution is then acidified, and the phenols are liberated and form an oily layer on the surface of the acid. This layer is separated, and the phenol recovered by a process of fractional distillation. It may be synthetically prepared by fusing potassium benzene sulphonate with caustic alkalis (A. Kekulé, A. Wurtz); by the action of nitrous acid on aniline; by passing oxygen into boiling benzene containing aluminium chloride (C. Friedel and J. M. Crafts, Ann. Chim. Phys., 1888 (6) 14, p. 435); by heating phenol carboxylic acids with baryta; and, in small quantities by the oxidation of benzene with hydrogen peroxide or nascent ozone (A. R. Leeds, Ber., 1881, 14, p. 976).

It crystallizes in rhombic needles, which melt at 42.5–43° C., and boil at 182–183° C.; its specific gravity is 1.0906 (0° C.). It has a characteristic smell, and a biting taste; it is poisonous, and acts as a powerful antiseptic. It dissolves in water, 15 parts of water dissolving about one part of phenol at 16–17° C., but it is miscible in all proportions at about 70° C.; it is volatile in steam, and is readily soluble in alcohol, ether, benzene, carbon bisulphide, chloroform and glacial acetic acid. It is also readily soluble in solutions of the caustic alkalis, slightly soluble in aqueous ammonia solution, and almost insoluble in sodium carbonate solution. When exposed in the moist condition to the air it gradually acquires a red colour. With ferric chloride it gives a violet coloration, and with bromine water a white precipitate of tribrom-phenol.

When phenol is passed through a red-hot tube a complex decomposition takes place, resulting in the formation of benzene, toluene, naphthalene, &c. (J. G. Kramers, Ann., 1877, 189, p. 129). Chromium oxychloride reacts violently on phenol, producing hydroquinone ether, O(C6H4OH)2; chromic acid gives phenoquinone, and potassium permanganate gives paradiphenol, oxalic acid, and some salicylic acid (R. Henriques, Ber., 1888, 21, p. 1620). In alkaline solution, potassium permanganate oxidizes it to inactive tartaric acid and carbon dioxide (O. Doebner, Ber., 1891, 24, p. 1755). When distilled over lead oxide, it forms diphenylene oxide, (C6H4)2O; and