376 



ANNALS NEW YORK ACADEMY OF SCIE\CES 



furnace, the presence of iron or lime or other bases that make fusible 

 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 destroys 

 the retort, and the bases are therefore 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 conceivable mineralogical aggregate that contained ten 

 per cent, of copper would be a very valuable ore, a zinc-bearing aggregate 

 with four or five times as much zinc might be unsalable. 



Suppose we compare them from another standpoint. Copper ores, if 

 at all profitable, are worth about so much per unit of copper, that is, so 

 much for each per cent. While there is some variation, yet the contrasts 

 as among three per cent., five per cent, and ten per cent, ores are much 

 the same as the ratio of the ]3er cents to each other. But if we think of a 

 zinc-blende ore or concentrate of 60 per cent, as the standard of richness, 

 a fifty per cent, ore is not worth five sixths as much, nor a forty per cent. 

 ore two thirds. On the contrary, a forty per cent, ore might be entirely 

 unsalable. As the zinc decreases, other deleterious bases take its place, 

 and a worthless mixture soon results. Zinc is in many ways the most 

 peculiar of the metals, and when we come to deal with its profitable treat- 

 nient analogies with other metals fail. 



In 1907, the United States was the chief producer of zinc among the 

 nations, but, as a rule, Germany leads, followed by this country and Bel- 

 gium in the order named. In later years, our output has varied from 

 26 to 30 per cent, of the total. As a rule, Germany is 3-4 per cent, in 

 excess of us and Belgium is 4-5 per cent. less. 



In America, Missouri is the chief source of zinc. Its. production from 

 tlie mines in 1908 was approximately one half the output of the entire 

 United States. New Jersey follows with somewhat over one quarter the 

 total, while all the rest are much smaller. 



The Missouri ores as thus far produced have been obtained from com- 

 paratively shallow depths. They extend lengthwise and sometimes later- 

 ally to greater dimensions than vertically. While it is not beyond the 

 possibilities that lower lying deposits may be discovered, since zinc ores 

 are found in Arkansas in strata of lower geological position, anticipations 

 of this reserve have not as yet been demonstrated on a large scale. Kan- 

 sas, Oklahoma and Arkansas, the states neighboring to southwest Mis- 

 souri, also liave some zinc ores, but they are not of great importance ; 

 southwestern Wisconsin is a very old mining district and has many small 

 mines, which were earlier worked for lead. Thev have been revived for 



