CAR

CAR

( 235 )

which are clofed up again. In this manner thefire is conduced to the bottom of the pile inthe courfe of about a fortnight: at this periodthe pile is covered up as accurately as pollibletill the fire is compleatly extinguifhed. Thoi'epieces that are found to be not fufficiently char-red are called brands, and are employed as fuelfor the next fire.

The charcoal produced from the truncheonsis laid by itfelf, and fold under the name ofcharcoal; that from the brulh-wood is difpofedof at a lower rate, and is called in the London market finall coaL

Although charcoal prepared by either of theabove methods is fully adequate to all the pur-pofes of fuel to which this fubftance is applied,yet in the manufafture of gunpowder, and forlome other ufes, it is of eflential importance toprocure a charcoal of greater purity than com-mon. This was formerly done by feledfingHems of willow, alder, and fome other of theaquatic trees, and charring them in the ufualmanner, but with peculiar care. Of late, how-ever, a very confiderable improvement in thepreparation of the finer charcoal has taken placeby charring or diftilling the wood in clofed ironcylinders. For this purpofe a large cylinder ofcall iron fixed in mafonry over a grate, and

furnilhed at one end with a door capable of be-ing accurately clofed, and terminating at theother in a curved pipe, is filled with the chipsor faw-duft of any kind of wood ; the door be-ing then clofed and a fire lighted in the grate,the empyreumatic acid, and all the other vola-tile parts of the wood are driven off by the heat,which is increafed till the contents of the cylin-der are red hot. The fire is then withdrawn,the cylinder is allowed to cool, and a blackfhining and remarkably pure charcoal, in greaterquantity alfo in proportion to the wood em-ployed than by the ufual way, is procured, ad-mirably fitted for the ufe of the gunpowdermakers, and apparently poffeffed of the famequalities from whatever kind of wood it ismade.

The proportion of charcoal yielded by par-ticular woods is liable to be fo materially affect-ed by the age, and the drynefs of the wood andthe method in which it is charred, as rendersit almoft impofiible to obtain any correct refultsin the great way. The following table fromexperiments in the fmall way by Mr. Mufhet,®will however be found to be interefling, as allthe woods before being charred, were tho-roughly dried and prepared as nearly as pofliblein the fame circumftances.

afforded 26.8

— mahogany - - - -

-25.4

— laburnum - - -

-24.5

— chefnut - - - ——

-23.2

— oak - - - - - -

- 22.6

— American black beech -

- 21.4

— holly - - - -

19.9

— fycamore - - -

- 19-7

— walnut - - - -

-20.6

— beech - - - - ■-

- 1 99

- American maple - -

- 1 9 9

— Norway pine - - -

- 19.2

— elm - - - - -

J 9-5

— fallow - - - - -

— 18.4

— alh ----- -

— 17-9

— birch - - - - -

— 17.4

— Scottifh pine - - -

— 16.4

of charcoal, of a greyifh colour, refembling oak.

-tinged with brown, fpongy and firm.

-velvet black, compact, very hard.

-gloffy black, compaCt, firm.

-black, clofe, very firm.

-- fine black, compact, remarkably hard.

-dull black, loofe and bulky.

-fine black, bulky, moderately firm.

-dull black, clofe, firm.

-dull black, fpungy, firm.

-ditto..

--fhining black, bulky, very foft.

-- fine black, moderately firm.

■---velvet black, bulky, loofe and foft.

-fhining black, fpungy, firm.

velvet-black, bulky, firm.

Charcoal of wood, whatever care is taken inthe burning to drive off all the volatile products,can never be entirely pure, as it mull retain allthe earthy and metallic ingredients of the wood,the proportions of which vary from -jV to T V ofthe charcoal; for the more delicate operationsof chemiftry therefore, that fpecies of charcoal13 made ufe of which is procured from the com-

—-tinged with brown, bulky, moderately

firm.

bullion of oily or refinous fubftances, and isknown in commerce by the general name ofLamp-black

Lamp-black is prepared in large quantities bythe turpentine manufacturers from the impurerefin that remains after the diftillation of oil ofturpentine, and other refufe matters of the famekind. Thefe are burnt in iron pots, or in a fur-

« Phil. Mag. iii. p. 17,

2 G %