53G Mr. W. Bukcr on the Metallurgy of Lead. 



antimony or sulphur be present, the colour is somewhat masked 

 and a dull-coloured white lead is produced. That the presence 

 of iron has nothing whatever to do with this appearance, is mani- 

 fest from the fact that the lead containing only an inappreciable 

 trace of copper which gave pure white corrosions, contained quite 

 as much iron as the specimens which afforded pink corrosions. 



Proceeding upon the results given above, Derbyshire lead, 

 which, when properly smelted, contains from 2 ozs. to 5 ozs. of 

 copper per ton, was crystallized three or four times and pro- 

 duced remarkably pure lead. Numerous analyses have con- 

 firmed the fact that, in dealing with a metal containing up to 

 5 ozs. or perhaps 7 ozs. per ton, the copper is always concen- 

 trated along with the silver. But a most remarkable fact was 

 discovered upon applying this method of purification to lead 

 containing above 10 ozs. of copper per ton. 



Five tons of lead, containing 0*0774 per cent, of copper, or 

 25 ozs. per ton, were submitted to Pattinson's process. At the 

 fourth operation the following was the distribution of copper in 

 the charge : — 



Crystals 0*0574 per cent, copper 



Fluid lead drained from! n AKO e 



the crystals > ° 0526 " " 



At the sixth crystallization, — 



Crystals 0*0642 per cent, copper 



Fluid lead 0*0570 



proving that no concentration of copper in the fluid portion had 

 taken place. The lead, which was otherwise soft and fit for all 

 ordinary purposes, such as rolling into sheets and making pipes, 

 possessed a surface unmistakeably different from that of the 

 purest lead, the most marked difference being a somewhat irre- 

 gular depression or crumpling in a line along the direction of 

 the length of the mould. Other experiments with lead contain- 

 ing various proportions of copper have showed that when the 

 quantity is above a certain limit, which can only be more accu- 

 rately defined when a larger number of analyses have been made, 

 the crystallization process cannot be economically employed. 

 It still remains, however, a useful adjunct to refining-opera- 

 tions, when the lead operated upon has been smelted from ore 

 carefully selected to exclude the more coppery kinds. Lead- 

 smelters, besides, might do much for the purity of lead if their 

 charges were worked in such a manner as that, with good ore, by 

 keeping the temperature as low as possible, even at the sacrifice 

 of the yield of metal, most of the copper would go into the slags. 

 These would yield equally good common lead ; and the repu- 



