which divides the metal into globules, like (hot.Powdered charcoal is put over all, and the cru-cibles are then covered and luted up with amixture of clay or loam and horfe-dung.
The time required for heating the cruciblesand compleating the procefs varies confiderablyin different works, being determined by cuffom,by the quantity of materials, the fize of thecrucibles, and efpecially the nature of the cala-mine. In the great way from ten to twenty-four hours are required. At Holywell, in Fliut-lhire, about twenty-four hours are taken.
During the procefs, and efpecially towardsthe latter end, part of the reduced zinc whichefcapes abforption by the copper, finds its wayin vapour through the luting of the crucible-lids, and burns around them with the beautifulblue flame and denfe white fmoke peculiar tothis metal.
The heat required for brafs-making is fome-what lefs than what would be neceffary to meltlarge maffes of copper, brafs being the morefufible of the two, and, as it fhould feem, thevapour of zinc being able to penetrate copper asfoon as it is foftened by a full red heat. Whenthe byafs is judged to be compleat, and thefaturation of the copper with zinc to be as highas poflible, the heat is increafed to melt thewhole down into one clean mafs at the bottom,the crucibles are taken out and the metal pouredinto moulds. At Holywell, out of the fix cru-cibles ufed to one furnace, the quantity of brafsobtained is about as much as would fill one ofthem. This makes in fubfequent manufafturea Angle large plate, which is manufactured inthe fame way as copper plate. Or, more accu-rately, from forty pounds of copper and fixtypounds of calamine, about fixty pounds of brafsare obtained, befides the lofs of a good deal ofzinc by the unavoidable efcape of much of it inform of vapour through the pores of the lute orthe crucible-covers.
The above is the ufual procefs of brafs-makingin this country, and is eflentially the famewherever this alloy is manufactured, but withfome .variation as to the choice of ingredients,their proportions, the time of fufion, thefhape of the furnace and other fmaller circum-ftances.
At Goflar, in Saxony , where brafs is largelymade, the zinc is furnifhed not by a native cala-mine but the cadmia or fublimed oxyd of zinc,which is collected for this purpofe in a particu-lar part of the chimnies of the reverberatory
furnaces, in . which 'the Saxon lead ores and-blendes are roalted.
A great variety obtains in the refpective pro-portions of the ingredients. According toSwedenborg b they are, in Goflar, 30 parts ofcopper, 40 to 45 of cadmia, and twice thevolume of charcoal; at Paris , and in many of theFrench manufactories, they are, 35 of copper,35 of old brafs, 40 of calamine, and 20 to 25of charcoal; in Sweden , 30 of copper, 20 to30 of old brafs, and 46 of calamine, with char-coal fufficient; or, 40 of copper, 30 of oldbrafs, and 60 of calamine; and in England,generally about 40 of copper and 60 of calamine.The produCt of brafs varies alfo, but it feemsto be in few places fo great as in fome of theEnglifh works, where, as already mentioned,40 pounds of copper become in the procefs 60pounds of brafs. This fuperior quantity isaferibed partly to the goodnefs of the calamineand partly to the fmallnefs to which the copperis previoufly reduced by being poured meltedinto cold water, and thus affording a great fur 7face of metal to the action of the zinc vapour.
At Stolberg, c near Aix-la-Chapelle , wherebrafs is very largely manufactured, the fur-naces are cylindrical, and each contains eightcrucibles arranged in two tiers of four each.Thefe crucibles are fifteen inches high, twelveinches deep, and eight or nine inches wide.The proportions of ingredients are 40 lb. ofcopper, 65 lb. of calamine, and double its vo-lume ,of charcoal. After the fire has been keptup for twelve hours, the crucibles are uncovered,and a workman takes off with an iron trowelall the feurn and charcoal which fwim upon theliquid metal, and which is called arhjl. Whenexamined with a glafs, this is found to confifl:of calamine and copper particles, cohering to-gether but not compleatly united. The brafs re-fulting from this firfit procefs is coarfe, brittle, andunequal in texture, and requires a fecond fufion.before it is fit for ufe. For this purpofe thefame crucibles are again employed and are filled,firft with three handfuls of the mixture of cala-mine and charcoal, over which are put two orthree pounds of the impure brafs broken inpieces, then more calamine and charcoal, witha lump of the arkejl, and over all, calamine andcharcoal powder. The crucible is then ftronglyheated for two hours, after which the brafs isfit to be call into plates, which is done here inthe following manner. A mould is formed oftwo blocks of granite, five feet long, three and
Repertory, vol. *iv.