COJUTEPEQUE, ko-noo'til-palkti. The capi tal of the Department of Cuseathin. Salva dor, about 15 miles east of San Salvador (Map: Central America, C 4). It is situated north of the volcano Cojutepeque, and near Lake Ilo pango. The city has considerable transit trade. Cojutepeque, for a few years after 1554, when San Salvador was destroyed by an earthquake, was the seat of government of the Republic.
COKE (probably connected with cake). A hard, brittle, porous solid, of a blackish-gray color and more or less metallic lustre. It does not soil the fingers when rubbed, and gives no smoke when burning. It absorbs moisture from the air to a very great extent. In general, the operation of making coke consists of expelling by heat the gaseous elements of bituminous coal. The residue resulting consists chiefly of pure carbon. mixed with varying amounts of ash con taining sulphur and phosphorus, and is known as coke. In the manufacture of illuminating gas, coke is produced as a by-product (see GAS, IL LUMINATING) ; but this method is inadequate to produce the requisite qualityand amount, and the manufacture of coke is itself an industry of great and rapidly increasing importance. Coke, char coal, and anthracite coal are the fuels most used in metallnrgy„ and of these coke pos sesses the advantages and is without the dis advantages of the other two. Its hardness en ables it to sustain the weight of furnace charges, and its porosity helps to make it readily com bustible. Charcoal is too soft, while anthracite coal, which is in reality a natural coke, is hard enough, but is so dense in structure that its combustion is slow and its calorific energy mod erate. The superiority of coke is due to its cel lular structure. The walls are hard and vitre ous, and the tiny passages between afford free course for the oxidizing gases of the blast-fur nace. Besides its use in metallurgy, coke is an important fuel in other industrial operations, and it is being adopted for locomotives on some railroads. In 1899 the Boston and :Maine Railroad began using coke as a fuel. Its ad vantages are that it is smokeless and does not produce sparks, thus decreasing the number of fires caused by the locomotives. Coke is also employed as a filtering material in water and sewage purification, being used extensively for the latter purpose, particularly in English prac tice.
Not all bituminous coals can be made into coke, and much experiment and research on the part of chemists have been devoted to ascertain ing the necessary constituents of a good coking coal. It appears that the coking property of coal is independent of the constituents, such as moistm-e, fixed carbon, ash, and sulphur, which it contains, and depends wholly upon the rela tions and volumes of the elements composing the combustible matters of the coal. Just
what these relations and volumes are has not been definitely shown. In Continental Europe, where the manufacture of coke has been very highly developed, only a poor quality of coal is available, and much ingenuity has been expend ed in constructing furnaces suitable for this in ferior grade of material. In America there has been as yet an abundant supply of coal of the very best quality for coking purposes, the supply having been drawn chiefly from the Connellsville coal of Pennsylvania and the Pocahontas coal of Virginia. But with the increasing demand for coke for metallurgical and other purposes. the poorer grades of coking coal must be drawn upon.
The preliminary preparation of coal for the manufacture of coke is chiefly a cleansing and separating process. Some of the best coking coal requires no special treatment, but is charged into the coke - ovens direct from the mines. It is usually found advantageous, how ever, to break up the coal into small pieces, in order that the volatile matter may be utilized to the utmost extent. When the coal is not uni form in size. it is found that it cokes unevenly, the finer portion much more rapidly. When there is much slate in the coal, it is necessary to wash it; the slate separating itself from the coal in the process of washing, on ac count of its greater weight. Fire-clay also will be separated and washed out. Before washing, however, it is necessary carefully to sort the coal according to size. Various machines of great efficiency have been devised for crushing, sorting, and washing coal ready for the ovens, which are described in great detail, as are also the different forms of coke-ovens, by John Ful ton in his Treatise on. the Manufacture of Coke (Scranton, Pa., 1895). Three general methods have been followed in the process of transform Mg coal into coke. The first was the primitive and wasteful process, borrowed from the char coal-burners, of open-air burning. The coal is simply piled in a rectangular heap on the ground, with longitudinal and vertical hues run ning through it, in which enough wood is placed to ignite the whole mass of coal. The tire is lighted at the base of the vertical flues, and gradually extends through mass. When the mass ceases to flame it indicates that the gase ous matter has been expelled, and the tire is partially smothered by covering the heap with tine dust. Last of all, the mass is sprinkled with a hose, the water being at once converted into steam, which permeates the whole mass. This process of coke-making requires from five to eight days.