KEMP, GEOLOGY AND ECONOMICS 375 



once an extremely important source of lead, is now a comparatively small 

 contributor. Colorado, in former years our chief source, has dropped to 

 only a third of its one-time yield, and yet the total of the country has 

 gone quite steadily on. The fall in the price of silver was a hard blow 

 to the western lead miners and naturally not only cut off their profits but 

 raised the necessary percentage of metal in the ore. 



If we look ahead for a century or some such long period, we may not 

 feel assured that production can be maintained at present rates. There 

 may, of course, be new discoveries in lands not as yet fully explored. 

 Being distant from present centers of consumption as they necessarily 

 would be, their entry into the markets would imply higher prices so as to 

 meet the charges of freight. 



On the other hand, lead is a metal Avhich oxidizes or changes very 

 slowly. In its applications in the metallic state, it tends thus to accu- 

 mulate unless lost in use, as in the case of shot and bullets. It is exten- 

 sively employed in the manufacture of paint, and in this form is of course 

 never recovered. About two per cent, of the entire output is destroyed 

 to give us white and red pigments. 



It behooves us on the whole to be careful in the use of lead and to 

 avoid, when possible, its unnecessary sacrifice. 



Zinc is a metal of comparatively late introduction into commerce in 

 the large way. Although known for centuries, it has found its chief 

 applications in the last sixt}' years. There was no zinc mine in the 

 United States until approximately the year 1850, and from the Missouri 

 region whence we now obtain our chief supplies, the really serious con- 

 tributions began about 1870. Lead, indeed, was mined and prized long 

 before this, but the associated zinc ore was thrown one side on the dumps. 

 In the West, the same experience continued until much later. Zinc was 

 a nuisance in the metallurgical treatment of lead, and even the lead was 

 sought and smelted either because of its own silver contents or because it 

 made possible the treatment of other refractory silver ores. In the metal- 

 lurgical work, the zinc was volatilized or slagged off and was lost. In- 

 deed, one of our most serious metallurgical problems has been the success- 

 ful treatment of lead-zinc ores, and many investigators have addressed 

 themselves to its solution. ]v[ow that anxiety is beginning to manifest 

 itself regarding zinc supplies for the future, the desire to save it is 

 stronger than ever. 



Zinc, however, is a peculiar metal, and because of the exigencies of its 

 treatment, its ores must possess greater richness and greater purity than 

 those of other base metals. Thus in the case of copper, a ten per cent, 

 ore is in later days phenomenally rich, and as it can be smelted in a shaft 



