BRA 



BRA 



cold water, which dividcE it into very fcii.ill rounJtd Ihot-likc 

 frapitifiits. Powdered charcoal is put over all, and the 

 crucibles are covered and luted up. The brafs furnace has 

 the form of the fruftum of a hollow cone, or a cone with 

 the bafe downwards, and the apex cut off horizontally. At 

 the bottom of the furnace is a circular ginte, or perforated 

 iron plate, coated with clay and horfe-dung, to defend it 

 from the aiflion of the fire. The crucibles (land upon tha 

 circular plate, forming a circular row with one in the mid- 

 dle. The fuel, which in Eni^land is coal, is thrown round 

 the crucibles, and is thrown into the furnace at the upper 

 part of it, or the truncated apex of ilie cone. A perforated 

 cover, made of bricks or clay, and kept tojiether by iron 

 bars, is fitted to this opening. This cover fervcs as a regiiUr 

 to regulate the heat ; fo that when it is to be increafed, the 

 cover is to be partly or entirtly removed, and a free drauijlit 

 admitted to the external air, which pafTcs alou'^ an under- 

 ground vault to the a(h-hole, through the holes in the circu- 

 lar grate betwixt the crucibles, and through the upper 

 mouth, along with the fmoke and flame, into an area, where 

 the workmen (land, wliich is covered by a large dome with 

 a chimney to conc!u<il the fmoke out of doors. To diminifh 

 the heat, the regiller cover is put on the mouth of the fur- 

 nace, leaving tlitreby no other exit for tlie fmoke and flame 

 tiian the holes of the cover. The time requirite for healing 

 the crucibles varies confiderably in different works, being de- 

 termined chiefly by the nature of the calamine or other ore 

 of zirc employed, and alfo by the fize of the crucibles. In 

 the great way, at lead ten or twelve hours are required. At 

 Holywell about twenty hours are employed. 



During the proccfs, and efpecially towards the latter end, 

 part of the reduced zinc which efcapes, being abforbed by 

 the copper, finds its way in vapour through the crucible 

 lids, and burns around them with the beautiful blue flame 

 and white fuioke peculiar to this volatile metal. 



The heat required for brafs-making is fomcwhat Icfs than 

 what is nccclTary to melt copper, for brafs is more fufible 

 than copptr, and the zinc is able to penetrate copper when 

 kept at a full red heat. When the brafs is judged to be 

 made, the heat is increafed to fufe the whole down into one 

 niafs at the bottom, and the crucibles are then removed, and 

 the melted brafs poured out into moulds. At Holywell, fix 

 crucibles are uftd to one furnace; and the quantity of brafs 

 procured from them all is fnfficient to fill one of them. 

 This makes a fingle large brafs plate, which is manufaftured 

 in the lame way as copperplate. Or, more accurately, from 

 forty pounds of copper and fixty pounds of calamine, about 

 fixty pounds of brafs are obtained, befides that a confider- 

 able quantity of zinc bun-.s off in the procefs above-men- 

 tioned. 



The above is the ufual procefs of making brafs in moft 

 parts of England, and is efllnlialiy t!ie fame wherever this 

 alloy is manufa'ttured, but with fome variation as to the 

 choice of ingredients, their proportions, the time of fufion, 

 and other fmallcr circumftances. In Guflar in Saxony, in- 

 ftead of a native calamine, the cadmia, or fublimed oxyd 

 of znic is ufed, which is colleftcd in a particular part of 

 the chimnies of tlie reverberatory furnaces, in whicli the 

 lead ores and blendes are roafted. The proportions of the 

 ingredients alfo vary coniiderably. According to Sweden- 

 b''>rg, they are, in Goflar, 30 parts of copper, 40 to 45 of 

 cadmia, and twice the volume of charcoal ; in many of the 

 manufactories in France, 35 of copper, 35 of old brafs, 

 40 of calamine, and 20 to 25 of charcoal ; in Sweden, 30 

 of copper, 20 to JO of old brafs, and 46 of calamine, with 

 charcoal fuf&cient ; or 40 of copper, 30 of old brafs, and 

 to of calamine ; in this country, generally about 40 of cop- 



per, and 1^0 of calamine. The prodmft of brafs varies alfo 5 

 but it fecnis to be in few places fo great as in fome of the 

 works of England, where, as already mentioned, 40 pounds 

 of copper incrsafe to 60 pounds of brafs. This fupciior 

 quantity is afcribed to tiie fmallnefs to which the copper is 

 prcvioufly reduced by pouring it melted into water, whicli, 

 it fccm?, is not always praftifed elfcwhere, and probably 

 too to the goodnefs of the calamine. 



At Stolbcrg, near Aix la Cliapelle, where brafs is ma(!e 

 to a very great extent, the furnaces are cylindrical, and each 

 contains eight crucibles arranged in two tiers of four each. 

 The crucibles are fifteen inches high, twelve inches deep, 

 and eight or nine wide. The proportions are 40 pounds of 

 copper, 6'^ of calamine, and double its volume of cliar- 

 coal. After the fire has been kept up for twelve hours, 

 a workman takes oft with an iroi^ tiowel all the fcum and 

 charcoal which fwim upon the liq'.^d, and when cooled 

 form a mafs called wLeJl. This, examined by a glafs, is 

 found to confill of calamine and copper particles cohering 

 together, but not completely uniled. The brals refulting 

 from this firll procefs is coarfc, brittle, and unequal in tex- 

 ture, and requires a fecond infion, before it is fit to be 

 wrought. For this purpofe the fame ciTicibles are ajjain 

 employed, and are filled, firll with three handfuls of the 

 mixture of calamine and charcoal, over which are put two or 

 three pounds of the impure brals broken in pieces, tlien 

 more calamine and charcoal, with a piece of the nrhejl, and 

 over all the calamine and charcoal powder. They are then 

 heated ftronglv for two hours, after which the brafs is fit to 

 be call into plates. 



A fingle fufion, where the fire is kept up long enough, 

 and the materials are good, is certainly fufficient to make 

 good malleable brafs; but it is probable, that the finell forts 

 undergo a fecond operation with frefii calamine and char- 

 coal. Some fecrecy is, however, obferved by thofe indivi- 

 duals who have the reputation of making the very fined ar- 

 ticle. 



In the laboratory, by way of experiment, brafs may be 

 made in a much fhorttr time by ufing the fame materials, 

 that is to fay, copper-fhot buried in a mixture of calamine 

 and charcoal, putting the cnicible m a wind furnace, and 

 heating flowly for half an hour, till the zinc begins to burn 

 off in blue flame round the cover of the crucible, and then 

 raifing the fire, and heating biiflcly for an hour longer. 

 This procefs of cementation of copper is alfo Ihewn very 

 neatly by a fomewhat different management, as given by 

 Cramer. Put the mixture of calamine and charcoal into a 

 crucible ; cover it with a thin layer of clay, over which, 

 when dry, lay a thin plate of copper, and cover the whole 

 with fine charcoal powder, and a luted cover to the crucible. 

 Apply heat gradually, and the vapour of the reduced zinc 

 will life through the floor of clay, will penetrate the red- 

 hot copper above it, and convert it gradually into brafs, 

 which, at the end of the operation, will be found lying 

 melted upon the ftratum of clay ; a^d the increafe of weight, 

 which the copper will be found thus to have gained, will 

 afford a good prailical tcfl of the goodnefs of tiie calamine, 

 and its fituefs for brafs-making in the great way. 



B afs is wrought into plates by calling and laminating. 

 At Stolberg the plates are firll call i»to a mould formed of 

 two blocks of hard granite five feet long, three and a half 

 broad, and eight inciies thick. Thel> „re placed one above 

 the other, and the upper one is raiftd by a pulley, and 

 fmeared with cow-dung previous to calling. To give the 

 plate the requifite thickucfs, hoops of iron of different 

 dimenfions are adapted to the under ftonc, fo as to confine 

 the melted metal, and regulate its thicknefs. The ftones 



3 are 



