Mr. W. Baker on the Metallurgy of Lead. 535 



It might seem to the uninitiated that the lead then operated 

 upon was already sufficiently pure for all practical purposes, the 

 quantity of copper it contained amounting to only 0*0154 per 

 cent. , or 5 oz. dwt. 14 grs. per ton. Neglecting the small 

 quantities of iron, sulphur, and silver, we will confine our atten- 

 tion to the copper, which is the most objectionable impurity 

 that has to be removed. 



For a long time certain " brands " of lead have been preferred 

 to all others for such purposes as making white lead and glass- 

 maker's red lead. We may instance the lead made from the 

 Snailbeach Mines in Shropshire, which has enjoyed a repu- 

 tation for making good red lead for glass-makers. The best 

 selected lead of the Northumberland district has been also much 

 sought after by the manufacturers of white lead. Happily we 

 are now emancipating ourselves from the fashion of ascribing 

 peculiarities in the smelted metal to the " nature of the ore." 

 This term is perhaps useful enough in the mouth of the practical 

 smelter when explaining how the charge is worked in the fur- 

 nace, but in all cases it may be translated into more precise 

 language by a due methodical and scientific inquiry. As the 

 most remains to be known about iron of all the common metals, 

 it is exceedingly probable the " nature of the ore " will have for 

 some time to come to account for the nature of the pigs intro- 

 duced. 



A very small quantity of oxide of copper in the red lead is 

 found to impart a bluish shade to flint-glass. In some cases it 

 can hardly be pronounced blue, but at least the glass is wanting 

 in the pure watery lustre which is the perfection of " cristal." 

 It is almost incredible that so small a proportion as 3 oz. per 

 ton, or 0*009 per cent., should impart an undesirable tint ; yet 

 the evidence upon this point is conclusive. Some facts in refer- 

 ence to white-lcad-making will, however, quite corroborate this 

 statement. In making carbonate of lead by the method of fer- 

 menting tanners' bark and acetic- acid vapour, the corroded or 

 converted lead often presents a delicate pink tint. Close obser- 

 vation has shown me that this is invariably connected with the 

 presence of copper. Where the air has had more free access, the 

 pink colour disappears, or is replaced by a far more delicate blue, 

 indicating the passage from suboxide of copper (Cu 2 0) to prot- 

 oxide of copper (CuO). Finally, pure lead specially prepared, 

 which gave repeatedly pure- white corrosions on receiving the 

 addition of a very small proportion of copper, exhibited the cha- 

 racteristic pink tint when again submitted to the action of the 

 corrosive vapours. Providing the lead is otherwise pure, a pro- 

 portion of only 2\ ozs. per ton, or 0*0071 per cent, of copper, is 

 sufficient to produce a delicate but decided pink hue. Should 



