LEAD MITMAN. 



599 



therefore, the country's lead supply may be considered as being 

 obtained from five kinds of ores, as listed in the accompanying table, 

 while the mining districts exploiting them are scattered in many of 

 the States west of the Mississippi Eiver, as noted in the map (fig. 4). 



Sources of lead. 



Fig. 3.— Growth of the lead industry in the United States. Data from Mineral Industry 



and United States Geologicla Survey. 



The presence of silver in every type of ore is due to the fact that 

 practically all galena contains silver in chemical combination with 

 the lead. Zinc, copper, and gold, on the other hand, are derived 

 from minerals physically combined with galena. In addition to 

 the lead obtained direct from ores, a considerable amount is recovered 

 annually from secondary sources, such as scrap pipe, cable cover- 

 ings, storage-battery lead, and sheet lead. Eemelted scrap often 

 contains impurities, such as antimony and tin, and is not ordinarily 

 substituted for lead direct from ores unless its origin and uniformity 



is proven. 



A striking illustration of certain stages of development experi- 

 enced by the lead industry which are constantly recurring, is con- 



