COAL 



109 



alworbing importance of mineral or pit coul, tin- 

 word coal alone has come to be used in this 

 special signification (Ger. steinLaltlfn, l-'r. i-lmrl 

 ae terrc) 



I 18 ono of the most Important of all rocks ; 

 it consists chiefly of carbon, and is universally 

 regarded as of vegetable origin. Its geological 

 relations are noticed in tlie article CARBONIFEROUS 

 SYSTEM. It occurs in layers or beds, and is always 

 of a black or blackish-brown colon r. Some of the 

 varieties have a very considerable degree of vitreous 

 or resinous lustre, while others are destitute of 

 lustre ; some have a shell-like fracture, and others 

 have a highly cross-jointed structure, and are 

 readily bniken into cubical or rhoniboidal frag- 

 ments. The precise characters of coal as a rock 

 species are not easily defined, and Ixith in Britain 

 and other countries important cases have occupied 

 courts of law, in which this dilliculty was strongly 

 felt, as in the great Scottish lawsuit concerning the 

 Torbanehill Mineral or Boghead Coal (q.v. ). Coal, 

 indeed, is rather a commercial than a scientific 

 term, but in a general way we may define it as a 

 fossil fuel of black colour and stony consistency, 

 which, when heated in close vessels, is converted 

 into coke with the escape of volatile liquids and 

 gases. The variety known as blind coal or anthra- 

 cite no doubt gives off scarcely any volatile matter, 

 but this is because it has undergone a natural dis- 

 tillation through the action of subterranean heat 

 or of the proximity of intrusive igneous rock. We 

 may therefore divide coal into two primary divisions 

 namely: (1) Anthracite, which does not, and (2) 

 Bitwminout coal, which does, flame when kindled. 

 Anthracite (q.v. ) sometimes contains as much as 

 94, and if we exclude the ash, 98 per cent, of carbon, 

 and as this element decreases in amount it graduates 

 into a bituminous coal. The term anthracite is, 

 however, still applied to some coals which do not 

 contain more than 80 per cent, of carbon. Various 

 synonyms, such as stone coal, glance coal, culm, 

 and Welsh coal, are also used to designate this 

 substance, which is used chiefly for smelting pur- 



goses and for generating steam. In the United 

 tatcs it is also very largely used for domestic 

 purposes heating and eooiving. It is difficult to 

 kindle, but gives out a high heat in burning. Bitu- 

 minous coal includes an almost endless number 

 of varieties, one of the best marked being cannel 

 or parrot coal. Cannel coal is probably so called 

 from burning with a bright flame like a candle, 

 and the name parrot coal is given to it in Scot- 

 land from the crackling or chattering noise it 

 makes when burned. That of different localities 

 varies much in appearance, but it is most commonly 

 dull and earthy, or with only a slight lustre ; some 

 examples are, however, bright and shining. In 

 texture it is nearly always compact, and certain 

 beds of it admit of being polished in slabs of con- 

 siderable size, which approach black marble in 

 appearance. Of this material vases, inkstands, 

 boxes, &c. are made. Cannel coal contains a large 

 percentage of ash, but the best cannels are in some 

 places much used for open-grate fires in houses. 

 Cannel is for the most part consumed in making 

 gas, of which it yields from 8000 to 15,000 cubic 

 Feet per ton. When distilled at a low red-heat it 

 yields paraffin oil. The other varieties of bitu- 

 minous coal are so numerous that, as an Admi- 

 ralty report states, there are as many as seventy 

 denominations of it imported into London alone. 

 Still, among these there are three leading kinds 

 1. Caking coat, which cakes or fuses into one 

 mass in the fire. It breaks into small uneven 

 fragments, and is found largely at Newcastle 

 and some other localities. 2. Splint or hard coal, 

 occurring plentifully in Scotland, which is hard, 

 and breaks into cuboidal blocks. This is often 



called block-coal ; and locally it i very valuable, be- 

 cause it can he. employed in smelting without t>eing 

 first coked. It is not very easily kindled, but when 

 lighted makes a clear lasting* fire. 3. Cherry or 

 soft rim/, which breaks easily into small irregular 

 <iil.cs. has a beautiful shining lustre, is readily 

 kindled, and gives out a cheerful flame and heat. 

 It is common in Staffordshire. Brown coal or 

 Lignite (q.v.), though for the mo>t part inferior to 

 true coal, is nevertheless an important fuel in some 

 countries in default of a better kind. There are, 

 however, large deposits of lignites in some regiotiH, 

 as in North America, which coke well, and which 

 are excellent substitutes for true coal. 



The use of coal does not seem to have been known 

 to the ancients ; nor is it well known at what time 

 it began to l>e used for fuel. Some say that it was 

 used 1 >\ the ancient Britons ; and at all events it 

 was to some extent an article of household con- 

 sumption during the Anglo-Saxon period as early as 

 852 A.D. There seems to be reason for thinking 

 that Britain was the first European country in 

 which coal was used to any considerable extent. 

 A coal-pit at Preston, Haddington, was granted 

 to the monks of New battle between 1210 and 1219. 

 Henry III. is said to have granted a license to dig 

 coal in 1234. About the end of the 13th century it 

 began to be employed in London, but at first only in 

 the arts and manufactures ; and the innovation was 

 complained of as injurious to human health. In 

 1306 the parliament petitioned the king to prohibit 

 the use of coal, and a proclamation was accordingly 

 issued against it ; but owing to the high price 

 of wood, its use soon became general in London. 

 It was for a long time known there as sea-coal, 

 because imported oy aea. 



Several theories as to the mode of the origin of 

 coal have been put forth from time to time. The 

 one now generally believed in is that the rank and 

 luxuriant vegetation which prevailed during the 

 carboniferous age grew and decayed upon land but 

 slightly raised above the sea ; that by slow sub- 

 sidence this thick layer of vegetable matter sunk 

 below the water, and became gradually covered 

 with sand, mud, and other mineral sediment ; that 

 then, by some slight upheaval or gradual silting up 

 of the sea bottom, a land surface was once more 

 formed, and covered with a dense mass of plant-, 

 which in course of time decayed, sank, and became 

 overlaid with silt and sand as before. At length, 

 thick masses of stratified matter would accumulate, 

 producing great pressure, and this, acting along with 

 chemical changes, would gradually mineralise the 

 vegetable layers into coal. Microscopical examina- 

 tion shows tliat coal consists principally of the corti- 

 cal portions of plants more especially of the bark of 

 such trees as Sigillaria commingled with the debris 

 of various other plants, amongst which the spore 

 cases and spores of certain lycopodiaceous trees not 

 infrequently occur in great abundance. It seems 

 probame indeed that many coal-seams simply repre- 

 sent great swamps and marshy jungles. 



As will be seen from the following table, wood, 

 peat, lignite or brown coal, and true coal indicate 

 by their composition the changes which vegetable 

 matter undergoes by decay and pressure ; and a 

 table in which a considerable number of examples 

 of each substance could be given would show now 

 gradually these substances pass into each other : 



Wood. P*t LinlU. CotL 



Carbon 60-0 60-0 65-7 82-8 



Hydrogen 6-2 6-5 5-3 5-8 



Oxygen 4S-8 33-5 29-0 11-8 



100-0 100-0 100-0 100-0 



In each of these bodies there is usually a small per- 

 centage of nitrogen, which in the above table lias 

 not been separated. In passing from wood or peat 



