LEAD 57 



The ores smelted at Holyvrell are very refractory galenas, mixed with blende, cala- 

 mine, pyrites, carbonate of lime, &c., but without any fluoride of calcium. They serve 

 mutually as fluxes to one another. The coal is of inferior quality. The sole of each 

 furnace is formed of slags obtained in the smelting, and they are all of one kind. In 

 constructing it, 7 or 8 tons of these slags are first thrown upon the brick area of the 

 hearth ; are made to melt by a brisk fire, and in their stiffening state, as they cool, they 

 permit the bottom to be sloped and hollowed into the desired shape. Four workmen, 

 two at each side of the furnace perform this task. 



The ordinary charge of ore for one smelting operation is 20 cwts., and it is introduced 

 through the hopper. An assistant placed at the back doors spreads it equally over the 

 whole hearth with a rake ; the furnace being meanwhile heated only with the declining 

 fire of a preceding operation. No regular fire is made during the first two hours, but 

 a gentle heat merely is kept up by throwing one or two shovelfuls of small coal upon 

 the grate from time to time. All the doors are closed, and the register-plate of the 

 chimney lowered. 



The outer basin in front of the furnace is at this time filled with the lead derived 

 from a former process, the metal being covered with slags. A rectangular slit above 

 the tap-hole is left open, and remains so during the whole time of the operation, unless 

 the lead should rise in the interior basin above the level of that orifice ; in which case 

 a little mound must be raised before it. 



The two doors in front furthest from the fire being soon opened, the head-smelter 

 throws in through them, upon the sole of the furnace, the slags swimming upon the 

 bath of lead, and a little while afterwards he opens the tap-hole, and runs off the me- 

 tallic lead reduced from these slags. At the same time his assistant turns over the ore 

 with his paddle, through the back doors. These being again closed, while the above 

 two front doors are open, the smelter throws a shovelful of small coal or coke cinder 

 upon the lead-bath, and works the whole together, turning over the ore with the paddle 

 or iron oar. About three quarters of an hour after the commencement of the operation, 

 he throws back upon the sole of the hearth the fresh slags which then float upon the 

 bath of the outer basin, and which are mixed with coaly matter. He next turns over 

 these slags, as well as the ore with the paddle, and shuts all the doors. At this time 

 the smelter lades off the lead into the pig-moulds. 



The assistant now turns over the ore once more through the back doors. A little 

 more than an hour after the operation began, a quantity of lead proceeding from the 

 slag last remelted is run off by the tap ; being usually in such quantity as to fill o'ne 

 half of the outer basin. Both the workmen then turnover the ore, with the paddles, 

 at the several doors of the furnace. Its interior is at this time of a dull red heat ; tho 

 roasting being carried on rather by the combustion of the sulphurous ingredients, than 

 by the action of the small quantity of coal in the grate. The smelter, after shutting 

 the front doors, with the exception of that next the fire-bridge, lifts off the fresh slags 

 lying upon the surface of the outside bath, drains them, and throws them back into 

 the furnace. 



An hour and a half after the commencement, the lead begins to ooze out in small 

 quantities from the ore ; but little should be suffered to flow before two hours have 

 expired. About this time the two workmen open all the doors, and turn over the ore, 

 each at his own side of the furnace. An hour and three quarters after the beginning, 

 there are few vapours in the furnace, its temperature being very moderate. No more 

 lead is then seen to flow upon the sloping hearth. A little coal being thrown into the 

 grate to raise the heat slightly, the workmen turn over the ore, and then close all the 

 doors. 



At the end of two hours, the first fire or roasting being completed, and the doors 

 shut, the register is to be lifted a little, and coal thrown upon the grate to give the 

 second fire, which lasts during 25 minutes. When the doors are now opened, the inside 

 of the furnace is of a vivid red colour, and the lead flows down from every side towards 

 the inner basin. The smelter with his rake or paddle pushes the slags upon that basin 

 back towards the upper part of the sole, and his assistant spreads them uniformly over 

 the surface through the back doors. The smelter next throws in by his middle door, a 

 few shovelfuls of quicklime upon the lead-bath. The assistant meanwhile for a quarter 

 of an hour works the ore and the slags together through the three back doors, and 

 then spreads them out, while the smelter pushes the slags from the surface of the inner 

 basin back to the upper part of the sole. The doors being now left open for a little, 

 while the interior remains in repose, the metallic lead, which had been pushed back with 

 the slags, flows down into the basin. This occasional cooling of the furnace is thought 

 to be necessary for the better separation of the products, especially of the slags from 

 the red bath. 



In a short time the workmen resume their rakes, and turn over the slags along with 

 the ore. Three hours after the commencement a little more fuel is put into the grate, 



