REPORT ON THE DEPARTMENT OF METALLURGY AND ECONOMIC 

 GEOLOGY IN THE U. S, NATIONAL MUSEUM, 1887. 



By F. P. Dewey, Curator. 



The principal work of the department during the year was the prep- 

 aration of a preliminary descriptive catalogue of the collections in 

 economic geology and metallurgy. 



Starting with the collections exhibited at the New Orleans exposition 

 as a foundation, they were expanded, and as many systematic series as 

 possible were constructed out of material in the Museum. 



These systematic collections are designed to show the actual occur- 

 rence of each metal, and the processes used in their extraction. To 

 these are added illustrations of the occurrences of non-metallic ores and 

 their utilization. 



The collections start, in the case of each metal, by showing the series 

 of minerals in which the metal forms an important constituent ; the 

 specimens are selected to show each mineral in its best perfection, in 

 order that it may be seen just how the metals occur in the ores. 



The next step is a series of ores selected to show the actually occur- 

 ring material that is mined, together with the associates of the ore. In 

 the case of the base metal, there may not be much difference between 

 the ore specimens and the mineral specimens, except the general purity 

 and perfection of the latter, and that an ore may contain several minerals 

 of the same, or even different, metals, especially alteration products, 

 which do not have a definite composition. 



In the case of the precious metals, however, there may be a wide dif- 

 ference between the two, depending upon the manner of occurrence of 

 the valuable portion of the ore. In the case of silver, one part distrib- 

 uted through a thousand parts of foreign material, may constitute a 

 paying ore; if now this one part be distributed through the remainder 

 evenly it will not be possible to detect any silver mineral in the ore, If, 

 however, the silver should be concentrated in separate portions through 

 the mass, it may be possible to pick out distinct silver minerals. 



The same observations apply to gold, but in a much greater degree, 

 since gold is so much more valuable, and in some cases can be extracted 

 at much less expense than silver; this is especially the case with the 

 hydraulic gravels of California, where, in some instances, an average 



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