Mr. H. L. Pjttinson on the Smelting of Lead Ore, §c. 171 



the Lead may be always introduced, on the side opposite to the gate- 

 way working at the time, to prevent the possibility of its being carried 

 by the stream of Litharge, over the breast of the test in its metallic 

 state ; and, in some instances, to be afterwards mentioned, where so 

 large a quantity of Lead is refined in a test, as to render it necessary to 

 have three gateways, the Lead is introduced through an opening be- 

 hind, during the time that the middle gateway is at work. 



The last part of the refining furnace to be noticed, is the aperture 

 behind, for the admission of a current of air, supplied by a powerful 

 double bellows, worked by machinery. This aperture is formed by a 

 conical iron tube k, Plate I. Fig. 3, called a muzzle, walled into the 

 brick-work forming the back of the furnace ; its larger end outwards, 

 receives the nozzle of the bellows, and its smaller end projecting into 

 the furnace, over the inner edge of the test, is bent down slightly, and 

 its orifice compressed into an oval form, so as to deliver the blast with 

 sufficient force upon the surface of the Lead, and at the same time to 

 spread it out towards the sides of the test. Much care is usually be- 

 stowed upon the construction of the muzzle, as the proper direction and 

 distribution of the blast, is a point of great consequence to the working 

 of the furnace. 



Refining furnaces are generally built double, that is one on each side 

 of the upright chimney ; but, excepting in the direction of the draught, 

 and consequent situation of the fire-places, there is no difference what- 

 ever between them. The fume and smoke from both, are conveyed in- 

 to a division of the horizontal flue, mentioned in pages 155 and 156, se- 

 parate from that containing the smoke from the roasting furnace, ore 

 hearth, and slag hearth, with which they are not suffered to mix. Here 

 they deposit a heavy grey powder, called refiner's fume, which is princi- 

 pally Oxide of Lead. 



The test being properly placed in its situation, cautiously dried, and 

 filled with Lead as already detailed, is exposed with its contents to the 

 flame passing over it, until the lead attains a bright red heat, at which 

 period the blast of air is made to play upon its surface. The oxygen 

 thus supplied, rapidly produces a stratum of fluid Litharge, which is 



