INDUSTRY, INVENTION. COMMERCE 



655 





lurgic operations. By cementation with char- 

 coal, iron is converted into steel. It is used in 

 the manufacture of gunpowder. In its finer 

 state of aggregation, under the form of ivory- 

 black, lampblack, etc., it is the basis of black 

 paint; and mixed with fat oils and resinous 

 matter, to give a due consistence, it forms the 

 osition of printing-ink. 



Clearing-house. The place where is 

 carried on the operation of clearing off balances 

 and adjusting daily accounts between bankers 

 of the same city; thus avoiding the inconveni- 

 ence of handling large amounts in currency or 

 convertible paper. Each bank, or banker, dis- 

 patches a clerk to the clearing-house, who there 

 draws up an abstract of the checks upon other 

 firms, and effects a clearance by exchanging 

 them against those drawn on the bank to which 

 he belongs. The balance is paid over in cash. 

 The first clearing-house in the United States 

 was established in New York in 1833. In Eng- 

 land, the railway companies, as well as the banks, 

 make use of the clearing system. 



Clay, The name of various earths, which 

 consist of hydrated silicate of aluminium, with 

 small proportions of the silicates of iron, calcium, 

 magnesium, potassium, and sodium. All the 

 varieties are characterized by being firmly co- 

 herent, weighty, compact, and hard when dry, 

 but plastic when moist, smooth to touch, not 

 readily diffusible in water, but when mixed not 

 readily subsiding in it. Their tenacity and duc- 

 tility when moist, and their hardness when dry, 

 has made them from the earliest times the ma- 

 terials of bricks, tiles, pottery, etc. Of the chief 

 varieties, porcelain-clay, kaolin, or china-clay, 

 a white clay with occasional gray and yellow 

 tones, is the purest. Potter's-clay and pipe- 

 clay, which are similar but less pure, are gener- 

 ally of a yellowish or grayish color, from the 

 presence of iron. Fire-clay is a very refractory 

 variety, always found lying immediately below 

 the coal; it is used for making fire-bricks, cru- 

 cibles, etc. Loam is the same substance mixed 

 with sand, oxide of iron, and various other for- 

 eign ingredients. The boles, which are of a red 

 or yellow color from the presence of oxide of 

 iron, are distinguished by their conchoidal frac- 

 ture. The ochres are similar to the boles, con- 

 taining only more oxide of iron. Other varieties 

 ller's earth, Tripoli, and boulder-clay, the 

 last a hard clay of a dark-brown color, with 

 rounded masses of rock of all sizes embedded in 

 it. the result of glacial action. The distinctive 

 property of clays as ingredients of the soil is 

 ;ower of absorbing ammonia and other 

 gases and vapors generated on fertile and ma- 

 nured lands; indeed no soil will long remain 



of coal in common use the combined effects of 

 pressure, heat, and chemical action upon the 

 substance have left few traces of its vegetable 

 origin ; but in the sandstones, clays, and shales 

 accompanying the coal, the plants to which it 

 principally owes its origin are presented in a 

 fossil state in great profusion, and frequently 

 with their structure so distinctly retained, al- 

 though replaced by mineral substances, as to 

 enable the microscopist to determine their botan- 

 ical affinities with existing species. The sigil- 

 laria and stigmaria, the lepidodendron, the cata- 

 mite, and tree-ferns are amongst the commoner 

 forms of vegetable life in the rocks of the coal 

 formation. Trees of considerable magnitude 

 have also been brought to light, having a recog- 

 nizable relation to the modern araucaria. The 

 animal remains found in the coal-measures indi- 

 cate that some of the rocks have been deposited 

 in fresh water, probably in lakes, whilst others 

 are obviously of estuanne origin, or have been 

 deposited at the mouths of rivers alternately 

 occupied by fresh and salt-water. The great 

 system of strata in which coal is chiefly found 

 is known as the carboniferous. There are many 

 varieties of coal, varying considerably in their 

 composition, as anthracite, nearly pure carbon, 

 and burning with little flame, much used for 

 furnaces and malt kilns ; bituminous (popularly 

 so called) or "household coal"; and cannel, or 

 "gas-coal," which burns readily like a candle, 

 and is much used in gas-making. All varieties 

 agree in containing from sixty to over ninety 

 per cent, of carbon, the other elements being 

 chiefly oxygen and hydrogen, and frequently a 

 small portion of nitrogen. Lignite, or brown 

 coal, may contain only fifty per cent, carbon. 

 For manufacturing purposes coals are generally 

 considered to consist of two parts, the volatile 

 or bituminous portion, which yields the gas used 

 for lighting, and the substance, comparatively 

 fixed, usually known as coke, which is obtained 

 by heating the coals in ovens or other close 

 arrangements. 



China and Japan contain about 200,000 square 

 miles of coal-fields; United States, 194,000; 

 India. 35,000; Russia, 27,000; Great Britain. 

 9,000; Germany, 3,600; France. 1,800; Bel- 

 gium. Spain, and other countries, 1,400. Total, 

 171,800, 



DISTRIBUTION OF COM. IN NIK UNITED 

 STATES 



Coal is found in commercial tjuantr 

 twenty-seven of the States and Territories >f 

 the United States and in Alaska. The following 

 table shows the area of coal-bearing formations 

 in the several States and the rank of the coal- 



