COAHUILA Y TEXAS COAL. 



283 



work is considerable. A very large sort of coaches, 

 called omnibus, has lately come into use, first in Paris, 

 and afterwards in London and elsewhere. They 

 serve as means of communication between different 

 parts of a city, and carry a large number of pas- 

 sengers, &c. Quite recently, a stage-coach began 

 to run from Paris to Orleans, containing sixty pas- 

 sengers. 



COAtfUILA Y TEXAS; a state or province of 

 Mexico, bounded E. by Tamaulipas, S. by New Leon, 

 S. W. by Durango, W. by Chihuahua. Its northern 

 boundary and extent are not well defined. It is wa- 

 tered by the Rio del Norte and its branches. The 

 chief towns are Montelovez and Saltillo. 



COAK. See Coal. 



COAL consists essentially of carbonaceous matter, 

 and, in one variety, the blind coal (see Anthracite), 

 this is nearly pure ; but, in the greater number of the 

 varieties of coal, there is present a soft, bituminous 

 matter, which communicates to them some peculiar 

 properties. Those which contain much bitumen are 

 highly inflammable, and burn with a bright flame ; 

 those in which the carbon predominates burn less vi- 

 vidly. Numerous varieties of coal exist, deriving 

 distinctions partly from their state of aggregation, 

 but principally from the proportions of their bitumen 

 and carbon. Excepting the anthracite, they may be 

 treated of under the two divisions of black coals and 

 brown coals. 



The colour of brown coal, as its name imports, is 

 brown : it possesses a ligneous structure, or consists 

 of earthy particles. The colour of black coalis black, 

 not inclining to brown, and it does not possess the 

 structure of wood. The varieties of brown coal are 

 the following: bituminous wood, which presents a 

 ligneous texture, and very seldom any thing like con- 

 choidal fracture, and is without lustre ; earthy coal, 

 consisting of loose, friable particles ; moor coal, dis- 

 tinguished by the want of ligneous structure, by the 

 property of bursting and splitting into angular frag- 

 ments, when removed from its original repository, 

 and the low degree of lustre upon its imperfect con- 

 choidal fracture ; common brown coal, which, though 

 it still shows traces of ligneous texture, is of a more 

 firm consistency than the rest of the varieties, and 

 possesses higher degrees of lustre upon its more per- 

 fect conchoidal fracture. Some varieties of black coal 

 immediately join those of brown coal. They are, pitch 

 coal of a velvet-black colour, or, generally inclining 

 to brown, strong.lustre, and presenting, in every di- 

 rection, a large and perfect conchoidal fracture ; slate 

 coal, possessing a more or less coarse, slaty structure, 

 which, however, seems to be rather a kind of lamellar 

 composition than real fracture ; foliated coal, resem- 

 bling it, only the lamina are thinner ; and coarse coal 

 in like manner, only the component particles are 

 smaller, and approach to a granular appearance ; 

 cannel coal, without visible composition, and having 

 a flat, conchoidal fracture in every direction, with 

 but little lustre, by which it is distinguished from pitch 

 coal. All these kinds are joined by numerous tran- 

 sitions, so that it often becomes doubtful to which of 

 them we should ascribe certain specimens, though 

 they undoubtedly are members of this species. 



As the preceding varieties of coal consist of varia- 

 ble proportions of bitumen and carbon, they, of 

 course, must vary in their inflammability. Several 

 varieties become soft, and others coke, when kindled, 

 or, in other words, allow of the separation of the bi- 

 tuminous from the carbonaceous part. We perceive 

 this separation in its combustion in a common fire ; 

 the coal, when kindled, swelling and softening, ex- 

 haling a kind of bitumen, and ourning with smoke 

 und light ; while, after a certain period, these appear- 

 ances cease, and it burns only with a red light. The 



separation is effected more completely by the appli- 

 cation of heat in close vessels : the bitumen is melted 

 out, and there is disengaged ammonia, partly in the 

 state of carbonate with empyreumatic oil, and the 

 coal gas (a variety of carburetted hydrogen), often 

 mixed with carbonic acid and sulphuretted hydrogen, 

 the carbonaceous matter being, in a great measure, 

 left, forming coke. 



The decomposition of coal is carried on, on a large 

 scale, with a view to collect the products ; the gas 

 being used to afford an artificial light, which is clear, 

 steady, easily regulated, and economical ; the bitumi- 

 nous matter, or mineral tar, being applied to the 

 uses for which vegetable tar and pitch are employed, 

 and the coked coal being used in the smelting of me- 

 tallic ores, and for various other purposes, where an 

 elevated and steady temperature is needed. 



Coal, excluding anthracite, has been supposed to 

 be of vegetable origin. There is a remarkable gra- 

 duation from bituminated wood to perfect coal. In 

 some varieties, the structure, and even the remains, 

 of plants are apparent, and its chemical composition 

 agrees with that of vegetable matter. It is difficult 

 to determine, however, in what manner it has been 

 formed, or by what operations the vegetable matter, 

 from which it has originated, has been so far modifi- 

 ed, as to have assumed the properties under which it 

 exists. And there are many geologists who regard it, 

 in common with anthracite, as an original mineral 

 deposit. 



The varieties called slate coal, foliated coal, coarse 

 coal, cannel coal, and pitch coal, occur chiefly in the 

 coal formation ; some varieties of pitch coal, also the 

 moor coal, bituminous wood, and common brown 

 coal, are met with in the formations above the chalk, 

 the earthy coal, and some varieties of bituminous 

 wood, and common brown coal, are often included in 

 diluvial and alluvial detritus. The coal seams alter- 

 nate with beds of slaty clay and common clay, sand- 

 stone, limestone, sand, &c. They are often associat- 

 ed with vegetable organic remains, in slaty clay; 

 sometimes, also, with shells, and having iron pyrites 

 intermixed with them. Bituminous coal is so uni- 

 versally distributed, that it is unnecessary to attempt 

 the enumeration of its localities. 



Coal, as an inflammable substance, appears to have 

 been known to the ancients, and to the Britons, be- 

 fore the Romans visited this island, it being found so 

 frequently hi ravines and beds of rivers, of a colour 

 and texture so decidedly different from the strata 

 which in general accompany it ; but as, at that pe- 

 riod, and for centuries afterwards, the country was 

 covered with immense forests, which supplied abund- 

 ance of fuel for every purpose of life, there was no 

 necessity for using coal as fuel. The working of 

 coal, therefore, only became an object of attention 

 as population and civilization advanced, when agri- 

 culture began to be studied, the woods cleared away, 

 and the arts of civil life cultivated ; accordingly we 

 find, that the working of coal in Britain, as an article 

 of commerce, is comparatively of modern date, and 

 appears to have commenced about the end of the 12th 

 century. The first charter giving liberty to the 

 town of Newcastle-upon-Tyne to dig coal, was grant- 

 ed by Henry III. anno 1 239 ; it was then denominat- 

 ed Sea-coal, on account of its being shipped for places 

 at a distance. In the year 1281, the Newcastle 

 coal-trade liad become so extensive and important 

 that laws were enacted for its regulation. In Scot- 

 land, coals began to be wrought much about the 

 same tune ; and a charter was granted in the year 

 1291, in favour of the Abbot and convent of Dunferm- 

 line in the county of Fife, giving the right of digging 

 coals in the lands of Pittencrieff, adjoining the con- 

 vent. From this period the working of coal gradu- 



