COP

COP

( 325 )

obftinacy, even long after it has affumed theappearance of a pure regulus, and even in veryfmall proportion they make the metal brittle,hard, and difficult to work.

There ate fcarcely two works in which pre-cifely the fame order is obferved in the differentreducing precedes (fuppofxng the quality of theore to be the fame) and as tire manufacturer isgenerally fatisfied with that which has beenlong eftabliihed and is attended with ordinaryfuccefs, he feldom enquires whether the labourmay be fhortened or the expence diminilhed.

The fulphuret of copper which is obtainedin fuch vaft quantities at the Parys mine inAnglefea, is wrought into rough copper in thefollowing manner. The ore is dug up inlarge pieces (being moftly obtained by blafting)and is firft broken into fmallift lumps by thehammer, chiefly by women and children, andput into a kiln from which proceed flues thatopen into a very long clofe pent-houfe galleryto colleCt the fulphur. The kiln is coveredclofe, and a little fire is applied to the mafs ofore in different places, whereby the whole isgradually kindled. The fulphur then rifes invapour to the top of the kiln, and thence throughthe flue into the long gallery, where it flowlycondenfes, and is afterwards brufhed out andfurther prepared for fale. The mafs of ore whenonce kindled continues to burn of itfelf with afmouldering heat for about fix months, duringwhich time the fulphur-chamber is cleared outfour times, after which the ore is Efficientlyroafted. The old fulphur-chambers are on alevel with the kilns and of the fame length andheight, or in fad they are a prolongation of thekilns: but the more modern and improvedchambers are like lime-kilns, the ore being atthe bottom, and the fulphur fubliming at thetop, with a contrivance to take out the roaftedore, and thus to keep up a perpetual fire.

The richeft part of the roafted ore is exportedwithout further preparation, but the pooreftpart is fmelted on the fpot. It ftill contains avaft quantity of fulphur and other impurities.The fmelting houfes are a range of large rever-beratory furnaces, thirty-one of which are underthe fame roof, ranged fide by fide in a Angle long row. They are all air furnaces, the chim-neys of which are 41 feet high, which caufes amoft powerful draught through them. Thefuel is coal, which is burned on a grate at theanterior part of the furnace, and the flame indrawing up the chimney paffes over the bed ofthe reverberatory, into which is put 12 cwt. ofthe roafted ore, previoufly mixed with a fmall

portion of coal duft. The ore is here melt-ed and reduced into a very impure regulus,and when Efficiently fufed it is drawn offthrough a plug-hole into earthen moulds. Afingle charge of the furnace, or 12 cwt. yields4 a cwt. of rough copper, which, by further pu-rification affords about 50 per cent, of puremalleable metal. The furnaces work off a finglecharge about every five hours.

The copper furnaces in Cornwall are alfo ofthe reverberatory kind. The ore when drawnup from the mine is firft broken into pieces nobigger than a hazel-nut, which operation iscalled cobbing, and the better fort is picked outby hand. The reduction begins by the procefsof roafting in large reverberatory furnaces 14feet by 16, the bottom or bed of which is madeof fire-bricks and covered to the thicknefs ofabout 2 feet with filicious fand, which runs to-gether by the heat into a femi-vitrified mafs.The chimney is from 40 to 50 feet high, whichcaufes fuch a powerful draught that the arfenicand fulphur feparated during the roafting pafsalmoft 1 entirely through the chimney into theopen air, none of it being collected as at Angle-fea. The ore is fpread over the bottom of thefurnace about a foot thick, being thrown inthrough a kind of funnel or hopper juft above.The fuel is Welfti coal, which, as ufual, isburnt at the anterior part of the furnace, andits flame draws over the Erface of the ore inits paffage to the chimney. In this furnace,which is called the calcining furnace, and is thelargeft of all, the ore is roafted without additionwith a dull red heat for 12 hours, and is fre-quently in that time ftirred with a long ironrake, introduced through a hole at the furtherend of the reberveratory, to expofe frelh furfacesto the aftion of the flame. The ore is notmelted here, but when roafted Efficiently, it iscarried to another furnace exactly fimilar to theformer, but fmaller, that is, about 9 feet by 6,and here it receives a fufing heat, but ftill with-out any addition, except that when the flag doesnot rife freely, a little calcareous fand is thrownin. At the end of every four hours the flag israked out •, it is then of the confiftence of foftdough and is laded into oblong moulds, and alittle water is fprinked upon it to make it finkdown, after which the moulds are quite filledwith it, and when cold it makes hard folid blocksof flag about 14 inches long and 12 deep andbroad, which are ufed for building. After theflag is raked off, a frefh charge of calcined oreis let down into the reverberatory, and the cop-per is tapped off by a hole in the fide of the