PROCESS FOR REFINING LEAD. 5 



of the furnace, which during the whole of the process had The btlghten- 

 beenvery obscure and misty, clears up. When the ope- *"§• 

 rator observes the surface of the silver to be free from 

 litharge, he removes the blast of the bellows, and sutfers 

 the furnace to cool gradually; as the silver cools many 

 protuberances arise on the surface, and fluid silver is Silver ejected 

 ejected from them with considerable force, which falling ^s it cooU. 

 again on the plate spots it very fantastically with small 

 globules. 



The latter portions of litharge bring over a consider- xhc last por- 

 able quantity of silver with them; this is generally re- tions of litharge 

 duced by itself and again refined. 



The litharge as it falls upon the floor of the refinery is The litharge 

 occasionally removed ; it is in clots at first, but after a flakes in cool- 

 short time as it cools it falls for the most part like slacked *^* 

 lime, and appears in the brilliant scales it is met with in 

 commerce : if it is intended as an article for sale, no- 

 thing more is necessary than to sift it from the clots 

 which have not fallen and pack it in barrels. 



If, on the contrary, it is intended to be manufactured It is reduced by 

 into pure lead, it is placed in a reverbatory furnace, vered" with *^°' 

 mixed with clean small-coal, and exposed to a heat just small-coal at a 

 sufficient to fuse the litharge. The metal as it is reduced ^o^^^'^te heat, 

 flows through an aperture into an iron pot, and is cast 

 into pigs for sale. During the reducing, care is taken to 

 keep the whole surface of the litharge in the furnace co- 

 vered with small-coal. 



In some smelt works, instead of a reverbatory furnace The reduction 

 for reducing, a blaSt furnace is made ufe of, on account is^est perform- 

 of the greater produce, but the lead so reduced is never furnace. 

 so pure as that made in the wind furnace. The oxides of 

 the metals, which require a greater heat to reduce than 

 the lead, are in the blast furnace generally reduced 

 with it. 



The volatile oxides, as zinc, antimony, and arsenic, are Volatile oxides 

 mostly carried oft' by evaporation during refining ; a con- 

 siderable portion of the oxide of lead itself is carried olF 

 by evaporation, making the interior of the. furnace so 

 misty and obscure that a person unused to refining cannot 

 see more than a few inches into it. 



A considerable portion of 'these oxides are driven by ^^''^''^'^ "P 'he 



^j^^ chimney. 



