Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/138

118 the churches of St Martin and St Eegula j the administra tive buildings ; and the hospital founded by Theodosius, a superior of the Capuchins. The prosperity of Coire is chiefly maintained by its transit trade between Germany and Italy ; but it also engages in the manufacture of cotton, wool, leather, and pewter wares, has dye-works and breweries, and deals in cattle and grain. The population, which is mainly Protestant, numbered 7552 in 1870.

1em  COJUTEPEC, a town of Central America, in the republic of San Salvador and the department of Cuscatlan, about 15 miles east of the capital. It has a population of about 15,000, and from 1854 to 1858 it served as the seat of government instead of San Salvador, which had been ruined by an earthquake. In 1872 it took part in a revolutionary outbreak against the existing Government, and the Indian population unsuccessfully attacked the garrison. The town gives its name to a neighbouring volcano, which rises to a height of 5700 feet, and also to the extensive lake, otherwise known as the Lake of Ilopango, which lies a few miles to the south and gives rise to the Rio Jiboa.  COKE, the carbonaceous residue produced when coal is subjected to a strong red heat, out of contact with the air, until the volatile constituents are driven off It consists essentially of carbon, the so-called fixed carbon, together with the incombustible matters or ash contained in the coal from which it is derived. In addition to these it almost invariably contains small quantities of hydrogen, oxygen, and nitrogen, the whole, however, not exceeding 2 or 3 per cent. It also contains water, the amount of which may vary considerably according to the method of manu facture. When produced rapidly and at a low heat, as in gas-making, it is of a dull black colour, and a loose spongy or pumice-like texture, and ignites with comparative ease, though less readily than bituminous coal, so that it may be burnt in open fire-places ; but when a long-continued heat is used, as in the preparation of coke for iron and steel melting, the product is hard and dense, is often prismatic in structure, has a brilliant semi-metallic lustre and silvery- grey colour, is a good conductor of heat and electricity, and can only be burnt in furnaces provided with a strong chimney draught or an artificial blast. The strength and cohesive properties are also intimately related to the nature and composition of the coals employed, which are said to be caking or non-caking according to the compact or frag mentary character of the coke produced. The simplest method of coking, that in open heaps or piles, is conducted in a very similar manner to charcoal burning. The coal is piled in a domed heap about 30 feet in diameter and 5 feet high, with a chimney of bricks arranged in open chequer work in the centre, around which the largest lumps of coal are placed so as to allow a free draught through the mass. The outside of the heap is covered with a coating of wet coke dust, except a ring about a foot high at the bottom. Fire is communicated by putting a few live coals near the top of the chimney, or from the interior by throwing them down the chimney, and the combustion proceeds downwards and outwards by the draught through the uncovered portion at the bottom. Whenever the fire takes too strong a hold and burns out to the surface it is damped by plastering over the spot with wet coke dust and earth, this being a point requiring con siderable skill on the part of the coke burner. When flame and smoke are no longer given off, which usually happens in from five to six days, the whole surface is smothered with coke dust, and the chimney is stopped for three or four days longer, when the heap is sufficiently cooled to allow of the coke being broken up and removed, or, as it is called, drawn. The cooling is usually expedited by throwing water upon the heap before drawing. The principle of coking in rectangular piles is generally similar to the fore going, but chimneys are not used. The dimensions generally adopted are a height of from 3J to 5 feet, and a breadth of 12 feet at the base. In coking by clamps or kilns a rectangular pile of coal is enclosed between upright walls, having a system of vertical and horizontal passages traversing them at intervals, which serve as chimneys to conduct the combustion through the pile. This system has been used at different times in Soutli W r ales, Germany, and other places, but is now generally abandoned, as the draught holes have a tendency to consume the coal unnecessarily unless very carefully watched. The largest proportion of the coke used for industrial purposes is made in close kilns or ovens. These vary very considerably in form and details of construction, but the same general principles are observed in all, the object being to effect the coking as much as possible by the consumption of the volatile inflammable gases given off above the surface of the coal, and to protect the latter from the direct access of currents of air. A further object is the utilization of the heat given off by the waste gases, which may be employed to heat the oven by circulating them in flues round the outside, and further by employing them for the accessory objects of raising steam, heating air, &c., in collieries and iron-works.

