SMELTING. 



by a water-wheel ; the ore is foon fmelted by the violence 

 of the fire, and the lead, as it is produced, trickles down a 

 proper channel, into a place contrived for its reception. 

 Thefe ore-hearths are now very rare ; though they are fre- 

 quently applied to the extradling lead from the flag which 

 is produced, either at the ore-hearth, or the cupola furnace, 

 and they are then called Jlag-htarths, and the lead thus 

 obtained is cMedJlag-lead ; the fire in a flag-hearth is made 

 of the cinder of pit-coal inftead of charcoal ; the furnace 

 called a cupol, or cupola, and rcverbtratory furnace, and by 

 the Germans a luind-furnace, in which ores are fmelted 

 by the flame of pit-coal, is faid to have been invented 

 about the year 1698, by a phyfician named Wright ; though 

 Becher may, perhaps, be thought to have a prior claim to 

 its invention, or introduftion from Germany. But who- 

 ever was the firft inventor of the cupola, it is now in 

 general ufe, not only in Derbyfhire and other counties for 

 the fmelting of ores of lead, but both at home and abroad, 

 where it is called the Englijb furnace, for the fmelting of 

 copper ores. This furnace is fo contrived, that the ore is 

 melted, not by commg into immediate contaft with the fuel, 

 but by the reverberations of the flame upon it. The bot- 

 tom of the furnace, on which the lead-ore is placed, is fome- 

 what concave, (helving from the fides towards the middle ; 

 its roof is low and arched, refembling the roof of a baker's 

 oven ; the fire is placed at one end of the furnace, upon an 

 iron grate, to the bottom of which the air has free accefs ; 

 at the other end, oppofite to the fire-place, is a high perpen- 

 dicular chimney ; the diredlion of the flame, when all the 

 apertures in the fides of the furnace are clofed up, is necef- 

 farily determmed, by the ftream of air which enters at the 

 grate, towards the chimney, and in tending thither it ftrikes 

 upon the roof of the furnace, and being reverberated from 

 thence upon the ore foon melts it. This furnace does not 

 require the ufe of bellows, and may, therefore, be con- 

 ilrufted any where. In fmelting lead-ore, they generally 

 put into the cupola furnace a ton of ore, previoufly beat 

 fmall and drelTed, at one time, wliich quantity they call a 

 charge ; and they work oft three charges of ore in every 

 twenty-four hours. In about fix hours from the time of 

 charging, the ore becomes as fluid as milk. In order to 

 obtain the lead free from the flag which fwims over it, the 

 fmelters ufually throw in about a bufliel of lime, which dries 

 up the flag, and prevents its running out with the lead. 

 The flag, thus thickened, is raked up towards the fides of 

 the furnace, and the lead guflies out through a hole in one 

 of the fides of the furnace, which having been properly flop- 

 ped during the fmelting of the ore, is opened for this pur- 

 jjofe into an iron pot, from which it is laded into iron 

 moulds, containing what they call a pig of lead ; the pigs, 

 when cold, being ordinarily llamped with the maker's name, 

 are fold under tiie name of ore-lead. After the lead has all 

 flowed out of the furnace, they (lop up the tap-hole, and 

 drawing down the flag and lime into the middle of the fur- 

 nace, they raife the fire, till the mixture of flag and lime, 

 which they fimply term Jlag, is rendered very liquid ; upon 

 this mafs they throw another quantity of lime, and proceed 

 as before. When the lead thus obtained, amounting gene- 

 rally to twenty or thirty pounds, is let out of the furnace, a 

 new charge of ore is |)ut in and the operation renewed. 



In order to fpare the time and expence of fuel, they have, 

 in fome furnaces, lately contrived a hole, through which they 

 fufl^er the main part of the liquid flag to flow out, before 

 they tap the furnace for the lead ; upon the little remaining 

 flag they throw a fmall portion of lime, and draw the mix- 

 ture out of the furnace without fmelting it. This kind of 

 furnace they have nicknamed a moccuroni. 



Dr. Watfon has fuggelled fome improvements in the con- 

 ftruAion of this furnace, and in the procefs of fmelting above 

 defcribed. He propofes to fubftitute an horizontal chimney 

 in the place of the perpendicular one now in ufe, and that 

 the end fartheft from the fire fliould be turned up by a 

 tube of earthen-ware, or otherwife ; fo that the fulphureous 

 acid, fet at hberty during the burning of the fulphur, may 

 iflue out in a diredion parallel to the flue of the chimney, 

 and at the diftance of about one foot and a half above it. 

 Let a number of large globular veflels be made either of glafs 

 or lead, each of which muft have two necks, fo as to be 

 capable of being inferted into one another : let thefe veflels 

 be placed in the flue of the chimney, the neck of the firft 

 being inferted into the above-mentioned tube, and the neck 

 of the laft being left open, for fear of injuring the draught 

 of the furnace. Let each of thefe globular veflels contain 

 a fmall quantity of water, in which cafe, he apprehends, 

 that the heat of the flue will raife the water into vapour, and 

 that this watery vapour will be the means of condenfing the 

 fulphureous acid vapour, in fuch a degree as to render the 

 undertaking profitable. When the fulphur is all confumed, 

 the draught of the furnace may be fuffered to have its ordi- 

 nary exit at the end of the horizontal chimney, by a very flight 

 contrivance of a moveable damper. 



The fame ingenious writer alfo obferves, that very ful- 

 phureous ore fliould be roalled for a long time with a gentle 

 heat. He alfo propofes to leave as little lead as poflible in 

 the flag ; for this purpofe he fuggelts, that it might be 

 ufeful to throw a quantity of charcoal-duft upon the liquid 

 fcoria in the cupola furnace, in order that the calcined lead 

 might be converted into lead, by uniting itfclf to the inflam- 

 mable principle of the charcoal ; and that it might be alfo 

 ufeful to flux fulphureous lead-ores in conjunftion with the 

 fcales or other refufe pieces of iron, or even with fome forts 

 of iron-ore. 



The fmelter nfight farther find it worth his while to re- 

 duce the flag into a powder by a ftamping mill, or to grind 

 it by any other contrivance, and then he may fcparate the 

 ftony part of the flag from the metaUic, by wafliing the whole 

 in water, inafmuch as the metallic part is heavier than the 

 other. Watfon's Chem. Efl". vol. iii. p. 253, &c. 



The other furnaces ufed in fmelting are fupplied with 

 large bellows, moved by the arbor of a wheel, which is 

 turned round by a current of water. Thefe have obtained 

 different names, according to fome difference in their con- 

 ftruftion. Their greater or lefs height gives occafion alfo 

 to the diftinftion of high furnaces and middle furnaces. The 

 high furnaces are of modern invention ; they were firft intro- 

 duced at Mansfelt in 1727, and are now ufed in almolt all 

 countries where ores are fmelted, as in Saxony, Bohemia, 

 Hungary, &c. They contribute, by their great height, being 

 above eighteen feet high, which allows the ore to undergo a 

 roalling by di|Terent degrees of heat before it is melted, to 

 Amplify and diminifli the labour. They are chiefly em- 

 ployed for crude fufions, and particularly for the flate 

 copper-ore. 



In order to facilitate the extraftion of metallic (ubflances 

 from the ores and minerals containing them, fome operations, 

 previous to the fufion or fmelting of thefe ores and minerals, 

 are generally nccefl'ary. Thefe operations confi It of, i. The 

 feparation of the ores and metallic matter from the .idhering 

 unmetallic earths and ilones, by hammers, and other me- 

 chanical inftruments, or by wafliing with water. 2. Their 

 divi/!on or rcduftion into fmaller parts by contufion and 

 trituration, that by ■.inotlur waihing with water they 

 may be more perfeftly cleanfcd from extraneous matters, 

 and rendered filter for the fubfcquent opcratiouE. 3. Roaji- 



