]Q| On Smelting of Lead. 



to the smelter. In the common method of smelting lead 

 ore there is no appearance of the sulphur it contains ; it is 

 consumed by the flame of the furnace, as soon as it is se- 

 parated from the ore. An attentive observer may, indeed, 

 by looking into the furnace, distinguish a diversity in the 

 colour of the flame at different periods of the process. 

 During the first three or four hours after the ore is put into 

 tl;e furnace, the flame has a blueish tint ; proceedmg, no 

 doubt, from the sul[)hnr, which, in being sublimed from 

 the ore, is inflamed ; after all the sulphur is separated from 

 the ore, the flame has a whitish cast; and then, and not 

 before, the fire may be raised for finishing the operation ; 

 for if the fire Be made strong before the sulphur be dis- 

 persed, the quantity of lead is less, probably for two 

 reasons; the sulphur unites itself in part to the lead which 

 is formed, and by this union becomes inseparable from it; 

 for the sulphur cannot without much difficulty be separated 

 from an artificial mixture of lead and sulphur, when the 

 two ingredients have been fused together. 2. The sulphur 

 whilst it continues united to the lead in the natural ore, 

 renders the ore volatile, so that in a strong heat a great 

 portion of it is driven off. Hence, very sulphureous ores 

 should he roasted for a long time with a gentle heat ; and in 

 this prcpi?r management of the fire principally consists the 

 superiority of one smelter above another. 



" An old lead smelter informed me that he had often re- 

 duced a ton of ore to 16 hundred weight, by roasting itj 

 but that he did not obtain more metal from it by a subse- 

 quent fusion, than if he had fluxed it without any previous 

 roasting. This may be true of some sorts of ore, but it is 

 not true of very sulphureous ores. Indeed the fire may be 

 so regulated in a cupola furnace, as to make it answer the 

 purpose of a roasting and a smelting-furnace at the same 

 time. I have seen much lead lost by smelting a ton of sul- 

 phureous ore in eight hours; which might have been saved, 

 if the fire had at first been kept so gentle, as to have allowed 

 twelve hours for finishing the operation. 



"Sulphur cannot be separated from lead ore in close 

 vessels; and the lead ore melts with so small a degree of 

 heat, that there may be more difliculty in procuring the 

 sulphur from the ores of lead, than from those of copper or 

 iron: hovvever, 1 am far from thinking the matter im- 

 practicable, thou<zh I have not vet hit upon the method of 

 doing it; and the following reflections may, perhaps, lend 

 to supersede the neceesity of collecting the sulphur in sub- 



»tance. 



** When 



