2 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



draulic gravels of California, where, in some instances, au average value 

 of 5 or 6 cents worth of gold in a ton 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 

 frequently long and costly operations are required to separate the dif- 

 ferent metals, while in the other cases their separation is quite easy. 

 In some cases a useful alloy can be smelted directly from ores contain- 

 ing more than one metal. 



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

 concentrating process in preparation for smelting. These i^rocesses 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 some of the valuable constituents, and the waste 

 material is rejected. In some cases ore of different metals occurring 

 together are separated from each other. Illustrations of these processes 

 form the next step in the series, and con sist of the ore as mined and 

 the product of each step in the dressing operations, including 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, and the products, waste products, and by- 

 products. To these in many cases are added various accessories, such 

 as materials of construction and tools. Where there are different 

 stages in the operation each stage is fully represented. To complete 

 this step a few illustrations of the application of metals are shown. 

 Several of these show metal working rather than metal producing. 



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

 metallic ores. 



The basis of these collections was exhibited at the New Orleans 

 Exposition, but they have been much enlarged and improved since 

 then. The collections described are but a beginning of the subject, and 

 while generally complete in themselves will require many additions to 

 even approach a full illustration of the subject. 



The collections are installed in the west half of the southwest conit 

 of the Museum. The accompanying diagram (PL. i) shows the ar- 

 rangement and method of installation. Numbers 1 and 2 are low flat 

 cases, the rest are upright cases, and the numbers refer to a single 

 panel or pair of doors. To examine the collection systematically one 

 should follow the dotted lines. 



