LEAD MITMAN. 



605 





from the fact that poles of green wood are immersed into the pot of 

 molten metal while it is still red hot. The poles have no metal- 

 lurgical function but as they burn, gases are given off which cause 

 the molten metal to churn and boil and thus expose large fresh 

 surfaces to the air so that it can oxidize the impurities. In their 

 converted form the impurities rise to the top of the molten metal as 

 a dross which is removed. The metal remaining in the pot which is 

 almost pure lead is then poured into molds ; that is, cast into bars of 

 approximately 100 pounds each in weight, called " pigs " and stored 

 or shipped to the markets as the case may be. 



Lead smelters and refineries are distributed quite widely over the 

 country as will be observed in the map shown on an earlier page, 

 but with more or less concentration at industrial centers, notably 

 San Francisco, St. Louis, Chicago, Pittsburgh, and in the vicinity of 

 New York. The same is true of lead products manufacturing plants. 



LEAD MARKETS. 



Lead is the purest of the more common base metals used in com- 

 merce, the impurities rarely exceeding one-tenth of 1 per cent. But, 

 even though almost pure, the kind and the amount of the impurities 

 contained determine the use to which the lead may be put as will be 

 observed in the accompanying table : 



Composition and uses of American pig leads. 



