C O A

( 59 7 )

C O A

COAL. a Kohle, Germ. Houille , Fr.

Mineralogids are by no means agreed in their„ arrangement of this important genus of mineralinflammables, we {hall therefore with the lefsfcruple differ in fome degree from them all.It appears to be upon the whole the moft con-venient as well as more conformable to natureto include both the carbonaceous and carbono-bituminous foffils under a Angle genus, fub-dividing it into the families of Brown Coal ,Black Coal, and Mineral Carbon .

* Brown Coal .. Imperfectly bituminous ; ofa brown colour, and vegetable texture.

Sp. I. Bituminized wood. Ligniform car-bonated wood, Kirw. Bituminofes holz, Werner.Bois bitumineux comtnun , Broch. Surturbrand,Iceland .

Its colour is brown approaching to brownifh-black. Its external fhape exactly refembles thatof comprefled trunks and branches of trees ; itsinternal texture is precifely that of wood, re-taining not unfrequently even the bark. Itsfradture in the fmall is fibrous, in the great,flaty. The principal fracture is glimmeringand lighter coloured than the crofs fracture,which is Alining, and fometimes imperfectlyconchoidal. Its fragments are fplintery, wedge-fhaped. It is opake, foft, gives a Alining ftreak,is fomewhat elaAic and flexible, and almoftlight enough to float on water. It bums witha clear flame though with but little heat, andgives out a bituminous odour often mixed withthat of fulphur.

The Surturbrand of Iceland , according toBergman, contains 58 per cent, of watery andvolatile inflammable matter, the carbonaceousand earthy refidue amounting to 42 per cent. Inthe bituminized wood of Rollo, Vauquelin found

54. vegetable earth,

10.7 fulphat of iron,

0.8 fulphur,

12.7 oxyd of iron,

0.7 fulphat of lime,

0.2 filex.

100.0

Bituminized wood occurs ufually in alluvialland among the beds of common brown coal;fometimes alfo forming beds by itfelf: in thePruflian amber mines it forms the dratum im-mediately above the amber, and nodules and

* Brochant, Kinv:

dalaclites of this beautiful fub(lance are gene-rally found intermixed. It is alfo met with indifperfed fragments in alluvial clay. It aboundsalfo in the neweft fioetz-trapformation, andforms mafles in limeftone and l'andilone belong-ing to the independent coal-formation.

It is found in Britain at Bovey, near Exeter,in the ifles of Skye and Cannay, in the coalArata of Mid-Lothian ; in Bohemia and variousparts of Germany; in France, Iceland , andRuflia.

It pafles into common brown coal and pitchcoal, and is occafionally penetrated by quartz.It is employed as a fuel, but is greatly inferiorto black coal.

Sp. II. Earthy Brown-coal. Scaly and earthycarbonated wood, Kirw. Erdkohle of Werner.Bois bitumineux terreux, Broch.

Its colour is blackilh or wood-brown or yel-lowifh-grey : it occurs in mafs, of a confidencebetween folid and friable. It is without luftreexcept when rubbed or cut, and then it becomesfomewhat Alining. It foils the fingers a little:its frafture is intermediate between uneven andfine earthy. It is very foft and falls eafily topieces. Sp. gr. a little greater than that ofwater.

It readily takes fire and burns with a weakflame and difagreeable bituminous odour. Al-cohol when digefted with it takes up a brownifiibitter fubftance, analogous to vegetable extract:by diftillation it yields a yellow empyreumaticoil, foluble in alcohol, and which when deprivedof its moilture by a gentle heat, acquires theconfidence of butter or cerate.

It contains from 15 to 20 per cent, of earthand oxyd of iron, the remainder being waterand inflammable matter. It often contains py-rites, and then pafles into the earthy ore ofalum, alaunerde, which fee.

It is found in fimilar fituations with the pre-ceding fpecies : in the neighbourhood of Leipfigit occurs in beds from 20 to 40 feet thick, andof great extent.

It is ufed as an inferior kind of fuel, efpe-cially in manufactories where a low degree ofheat is required •, for this purpofe it is moidenedwith water, well beaten and made into brick-fhaped mafles. In the vicinity of Cologne avariety is found of a rich reddilh-brown colour,which is prepared as a pigment under the nameof Cologne umber.

Sp- III. Common Brown-coal. Compacl car-bonated wood, Kirw. Genuine braunhhl, Werner.Houille brune, Broch. Bovey coal.

Its colour is light brownifh black palling into

n, Jamefon, Hauy.

2 P

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