156 EEPORT OF NATIONAL MUSEUM, 1887. 



value of five or six cents worth of gold in a cubic yard of the gravel has 

 yielded a profit. 



The gangue or material carrying the valuable mineral varies greatly, 

 and exercises much influence upon the processes to be followed in the 

 extraction of the metal. 



In many cases an ore contains more than one valuable metal, and, fre- 

 quently, long and costly operations are required to separate the different 

 metals, while in other cases their separation is quite easy, and in some 

 cases a useful alloy can be smelted directly from ores containing more 

 than one metal. 



After the ore is mined it is frequently subjected to some kind of a con- 

 centrating process in preparation for smelting ; these processes vary 

 from simple sorting by hand, whereby much worthless material is re- 

 moved, to very elaborate treatment by machinery, whereby the valuable 

 portion of the ore is concentrated to a smaller volume and weight, gen- 

 erally with a loss of a small portion of the valuable constituents, and the 

 waste material is rejected, and in some cases, ores of different metals oc- 

 curring together are separated from each other. Illustrations of these 

 processes form the next step in the series, and consist of the ores as 

 mined, and the products of each step in the dressing operations, includ- 

 ing both the valuable and the waste products. 



The final step of the series represents the processes of extracting the 

 metals from their ores and converting them into useful forms. These 

 collections include the ores, the fuels, the fluxes, and all other materials 

 entering into the operation. Where there are different stages in the 

 operation, each stage is fully represented. 



The non-metallic ores are treated in the same general way as the me- 

 tallic ores. 



The collections shown at the New Orleans exposition have been ex- 

 panded to over 3,000 specimens, and the collections described are but 

 a beginning. While generally complete in themselves, they will require 

 many additions to even approach a full illustration of the subjects. 



After this catalogue had been prepared 1,840 labels were written for 

 the new material added to the collections. 



During the year 139 accessions were received. Of these the most im- 

 portant were : 



A large amount of tin ore and its associates from the Irish Creek lo- 

 cality in Rockbridge County, Virginia, presented by Mr. E. Willis, of 

 Charleston, South Carolina. 



A large collection representing the iron resources of Louisiana and 

 Texas, containing many specimens of ore and pig-iron, and a few speci 

 mens of coal, presented by Prof. L. C. Johnson, U. S. Geological Survey 



A large amount of the nickel and cobalt ores from Lovelock, Nevada 

 containing both the sulphide ore, and ores consisting essentially of ox 

 idized decomposition products, presented by George Lovelock, sr., Eeno 

 Nevada. 



