COP

COP

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The principal objeas of alloying copper ap-pears to be to render it lefs liable to tarnilh,and efpecially to be aaed on by common ani-mal or vegetable fubftances, (which, when ufedfor culinary purpofes, is of extreme importance):to make it more fufible, and harder, and ableto take a higher pclifh; and to alter its coloureither to a golden yellow or a filvery white. Allthefe objects are attainable by different alloys.

Copper ‘with Gold, Silver, and Platina .

Thefe are feldom if ever ufed in the propor-tions in which they would be alloys of copper,being much too coltly for any purpofe of manu-facture, confidering the great deterioration ofthe more valuable metals ; with this exception,however, that a very fmall portion of filvermuch improves the compofition of the alloy ofcopper and tin, when ufed as bell-metal or- fpe-culum-metaj. This will be afterwards noticed.Copper is ufed largely as an alloy of gold andfilver, and it is often plated with one or theother. This Abject we fhall refer to thefemetals refpcctively.

Copper with Arfe?iic.

Arfenic has beyond any other metal the effectof whitening copper, but as it is readily evapo-rated in fumes at lefs than a red heat, and there-fore at a temperature much below the meltingpoint of copper, fome management is requiredto effedt a combination of the two. For thispurpofe, firft melt the copper in a crucible,then wrap up in paper fome white arfenic mixedwith a little charcoal, or elfe regulinc arfenic, oreven white arfenic alone, or, as fome recommend,arfenic and potafh, and with a long pair of tongsthruft it to the bottom of the melted copper.The arfenic immediately rifes through the copper,and moft of it burns off in denfe white fumes,but a certain portion is retained. The mixturefliould be immediately cooled. It feems fome-vvhat a more convenient way to put the arfenicin a fmall crucible, inverting it over the meltedcopper and forcing it down to the bottom, hold-ing it there till all the arfenic has palled through.®By repeating this feverai times, the copper mayprobably be more fully faturated with arfenic,obferving each time to give no more heat thanrequifite.

This alloy is quite white, of a very clofe tex-ture, but perfectly brittle, and where the ar-fenic is fullicient entirely to deltroy the yellow.of the copper it is liable to tarnifli in the air,the more in proportion to the dole of arfenic.As foon as it melts the arfenic begins to efcape,

ejour. Plivf, tom. I. b An.Ch tom, 30. ' Gmeli

k Notes to

and on account of the extreme volatility of thisingredient it is impoffible to combine accurateproportions, fo that always enough arfenic muftbe ufed, to allow for a confiderable lofs. Whenkept long in fufion, the copper regains its malle-ability in proportion as the arfenic efcapes, buteven when it has become quite malleable, thecolour does not entirely return to the originalcopper-red, but long remains of a dingy yellow.

Vauquelin h has obferved, that when equalparts of filver and copper are alloyed (whichby themfelves make a pale yellow mixture) theaddition of fo little as 2 of arfenic to 100 ofthe alloy gives a perfect whitenefs, whilft theductility and malleability remains. Beyond 5per cent, of arfenic the alloy begins to be brittle,without increafing in whitenefs.

Arfenic is ufed in fmall quantity in fome ofthe more compound white alloys of copper, par-ticularly in fpeculum-metal.

Copper with Manganefe.

Attempts have been made to whiten copperand retain the malleability by alloying withmanganefe, but with little fuccefs. The com-bination is difficult, and feems to require twoproceffes. Firft, let copper and oxyd of man-ganefe with charcoal be mixed, and put into acrucible lined with charcoal, and heated veryintenfely. This gives a black, crumbly, granular,femi-metallic mafs, confuting of the metalspartly combined, and of fome of the charcoal.The whole of this again fufed under borax,gives a metallic button of a dirty yellowifhwhite, hard, and fomewhat malleable.'

If the combination is attempted by a fingleprocefs and a flux ufed, the manganefe andflux will melt together, and will corrode thecrucible king before any reduction can takeplace.

Copper with Iron .

Thefe only unite when the iron is in fmallquantity. The alloy is grey, hard, and fome-what brittle.

Tutenag is a white alloy of copper, zinc, andiron, according to Kcir, k which is very hard,tough, and fufficiently ductile to be wroughtinto various articles of furniture, fuch as candle-fticks, &c. which take a high polifh, and whenmade of the better fort of tutenag are hardly dif-■tinguifhable from filver. The inferior kindsare ltill white, but with a braffy yellow.

The Chinefe Petong is another fine, white,malleable alloy of copper, the compofition ofwhich is not exaftly known, but it contains a

n in Comment. Gotting, vol, 9. and own Experiments.Macquer .