LEAD 59 



hearth may now be considered in its regular working state, having a mass of heated 

 fuel, mixed with partly-fused and semi-reduced ore, called Bronze, floating upon a 

 stratum of melted lead. The smelting shift is then regularly proceeded with by the 

 two workmen, as follows : Tho fire being made up, a stratum of ore is spread upon 

 the horizontal surface of the bronze, and the whole suffered to remain exposed to the 

 blast for the space of aboiit five minutes. At the end of that time, one man plunges 

 a poker into the fluid lead, in the hearth bottom below the bronze, and raises the 

 whole up, at different places, so as to loosen and open the brouze, and in doing so, to 

 pull a part of it forwards upon the workstone, allowing the recently-added ore to sink 

 down into the body of the hearth. The poker is now exchanged for a shovel, 

 with a head 6 inches square, with which the brouze is examined upon the workstone, 

 and any lumps that may have been too much fused, broken to pieces ; those which are 

 so far agglutinated by the heat, as to be quite hard, and further known by their bright- 

 ness, being picked out, and thrown aside, to be afterwards smelted in the slag hearth. 

 They are called ' grey slags.' A little slaked lime, in powder, is then spread upon 

 the brouze, which has been drawn forward upon the workstone, if it exhibit a pasty 

 appearance ; and a portion of coal is added to the hearth, if necessary, which t})6 

 workman knows by experience. In the mean time, his fellow workman, or shoulder 

 fellow, clears the opening, through which the blast passes into the hearth, with a 

 shovel, and places a peat immediately above it, which he holds in its proper situation, 

 until it is fixed, by the return of all the brouze, from the workstone into the hearth. 

 The fire is made up again into the shape before described, a stratum of fresh ore spread 

 upon the part, and the operation of stirring, breaking the lumps upon the workstone, 

 and picking out the hard slags repeated, after the expiration of a few minutes, exactly 

 in the same manner. At every stirring a fresh peat is put above the nozzle of the 

 bellows, which divides the blast, and causes it to be distributed all over the hearth ; 

 and as it burns away into light ashes, an opening is left for the blast to issue freely 

 into the body of the brouze. The soft and porous nature of dried peat renders it very 

 suitable for this purpose ; but, in some instances, where a deficiency of peats has 

 occurred, blocks of wood of the same size have been used with little disadvantage. As 

 the smelting proceeds, the reduced lead, filtering down through all parts of the brouze 

 into the hearth bottom, flows through the channel, out of which it is laded into a 

 proper mould, and formed into pigs. 



The principal particulars to be attended to in managing an ore-hearth properly 

 during the smelting shift are these: First. It is very important to employ a 

 proper blast, which should be carefully regulated, so as to be neither too weak nor 

 too powerful. Too weak a blast would not excite the requisite heat to reduce the ore, 

 and one too powerful has the effect of fusing the contents of the hearth into slags. 

 In this particular no certain rules can be given ; for the same blast is not suitable 

 for every variety of ore. Soft free-grained galena, of great specific gravity, being 

 very fusible, and easily reduced, requires a moderate blast ; while the harder and 

 lighter varieties, many of which contain more or less iron, and are often found rich 

 in silver, require a blast considerably stronger. In all cases, it is most essential, that 

 the blast should be no more than sufficient to reduce the ore, after every other neces- 

 sary precaution is taken in working the hearth. Second. The blast should be as 

 much divided as possible, and made to pass through every part of the brouze. Third. 

 The hearth should be vigorously stirred, at due intervals, and part of its contents 

 exposed upon the workstone ; when the partially-fused lumps should be well broken to 

 pieces, as well as those which are further vitrified, so as to form slags, carefully picked 

 out. This breaking to pieces, and exposure of the hottest part of the brouze upon 

 the workstone, has a most beneficial effect in promoting its reduction into lead ; for 

 the atmospheric air immediately acts upon it, and, in that heated state, the sulphur 

 is readily consumed, or converted into sulphurous acid, leaving the lead in its metallic 

 state ; hence it is that the reduced lead always flows most abundantly out of the hearth 

 immediately after the return of the brouze, which has been spread out and exposed to 

 the atmosphere. Fourth. The quantity of lime sed should be no more than is just 

 necessary to thicken the brouze sufficiently; as it does not in the least contribute to 

 reduce the ore by any chemical effect : its use is merely to render the brouze less 

 pasty, if, from the heat being too great, or from the nature of the ore, it has a dis- 

 position to become very soft. Fifth. Coal should also be supplied judiciously ; too 

 much unnecessarily increasing the bulk of the brouze, and causing the hearth to get 

 too full. 



When the ore is of a description to smelt readily, and the hearth is well managed in 

 every particular, it works with but a small quantity of brouze, which feels dry when 

 stirred, and is easily kept open and permeable to the blast. The reduction proceeds 

 rapidly with a moderate degree of heat, and the slags produced are inconsiderable ; but, 

 if in this state, the stirring of the brouze and exposure upon the workstone are dis- 



