1 go On Smeliivg of Lead. 



damper. Since the first publication of the preceding Essay, 

 I have seen an horizontal chimney at the copper works near 

 Liverpool, where everv thing I had said concerning the pro- 

 bability of saving sulphnr by roasting lead ore, is verified 

 witli respect to copper ore; and I believe a patent has been 

 granted to son)e individual for this mode of collecting sul- 

 phur. Sulphur might be obtained with equal facility from 

 the pi/riles which is found amongst coal, and this applica- 

 tion of the pj-rites might, probably, be more lucrative than 

 the present one — making green vitriol. 



" A third circumstance, which requires the utmost care 

 of the lead-smtltcr, is the leaving as little lead as possible 

 in the slag. Near every smelling-house there are thousands 

 of tons of slag, which, when properly assayed, arc found to 

 vield from one-eighth to one-tenth of their weight of lead, 

 though no person has vet discovered a method of extracting 

 so much from them when smelted in large quantities; and 

 indeed the smelters are so little able to obtain all the lead 

 contained in them, that in many places they never attempt 

 to extract any part of it : in some places where thev do at- 

 tempt it, I have known the jiroprietor of the slag allow the 

 smelters 20j. for every pig of lead they procured of the 

 value of 38s. besides furnishing them with fuel : and yet 

 the men employed in such v^i unwholesome bu^uiess, sel- 

 dom made above 7s. a week of their labour. This fusion 

 of the slag of a cupola furnace is made, as has been men- 

 tioned, at a hearth furnace; (he coal cinder, which they 

 use as i'uel, and the slag are soon melted by the strong blast 

 of the bellows into a black mass, which, when the fire is 

 very strons;, becomes a perfect glass ; this black mass, even 

 in its most liquid state, is very tenacious, and hinders many 

 of the particles of lead from subsiding ; and it being from 

 time to time removed from the furnace, a considerable 

 quantity t)f lead is left in it, and thereby lost. A principal 

 part of the lead contained in the slag of the cupola furnace, 

 is not, I apjjrehend, in the forrn ot a metal, but in the form 

 of a litharge or calcined lead : a portion of the lead, in be- 

 ing smelted from its ore, is calcined by the violence of the 

 fire ; this calcined lead is not only very viirifiable of itself, 

 but it helps to vitrify the spar which is mixed with the ore, 

 and thus constitutes the liquid scoria; might it not be use- 

 ful to throw a qu intitv of charcoal dust upon the liquid 

 scoria in the cupola lurnacc, in order that the calcined lead 

 might be converted into lead by uniting itself to the in- 

 flammable principle of the charcoal ? Iron will not unite 

 with lead, biit it readily unites with sulphur ; and whtn 



added 



