Januaby 6, 1911] 



SCIENCE 



depths of nearly 2,000 feet beneath the 

 overlying surface and to be holding out 

 without essential change in character. In 

 Missouri, however, the mines never have 

 been very deep, that is over three or four 

 hundred feet, and the compensation comes 

 in wide horizontal extent. 



Some of the old time heavy producers 

 have greatly declined. Nevada, once an ex- 

 tremely important source of lead, is now 

 a comparatively small contributor. Colo- 

 rado, 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 west- 

 ern 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 pres- 

 ent rates. There may, of course, be new 

 discoveries in lands not as yet fully ex- 

 plored. Being distant from present centers 

 of consumption as they necessarily would 

 be, their entry into the markets would im- 

 ply higher prices so as to meet the charges 

 of freight. 



On the other hand, lead is a metal which 

 oxidizes or changes very slowly. In its ap- 

 plications in the metallic state it tends thus 

 to accumulate unless lost in use, as in the 

 case of shot and buUets. It is extensively 

 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 pig- 

 ments. 



It behooves us on the whole to be care- 

 ful in the use of lead and to avoid, when 

 possible, its unnecessary sacrifice. 



Zinc is a metal of comparatively late in- 

 troduction into commerce in the large way. 

 Although known for centuries, it has found 



its chief applications in the last sixty 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 contributions 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 metal- 

 lurgical 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 re- 

 fractory silver ores. In the metallurgical 

 work the zinc was volatilized or slagged off 

 and was lost. Indeed, one of our most seri- 

 ous metallurgical problems has been the 

 successful treatment of lead-zinc ores and 

 many investigators have addressed them- 

 selves to its solution. Now 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 

 furnace the presence of iron or lime or 

 other bases that make fl^sible slags is an 

 advantage. But zinc ores, perhaps after 

 preliminary roasting, must be reduced and 

 the metal must be volatilized at a high 

 temperature from a small charge in a 

 retort. The presence of fusible bases de- 

 stroys the retort and the bases are there- 

 fore debarred beyond certain small per- 

 centages. Thus it happens that a forty or 

 fifty per cent, zinc ore might be valueless 

 if "contaminated by iron or lime beyond a 

 narrow margin. While almost any con- 



