204 METALS. 



silver ore and mercury in South America and elsewhere 

 and often the igneous rock itself contains the same metals 

 disseminated through it. 



Gangue. — The rock immediately enveloping the ore i9 

 called the gangue, A vein often consists for the most part 

 of the rock material called the gangue ; and the ore either 

 intersects the gangue in a continued band, or more com- 

 monly, is partly disseminated through it in some places, and 

 is continuous for long distances in others. Often a good 

 vein gradually loses its character, the metal disappears, and 

 the gangue alone is left ; but by following on for some dis- 

 tance, it will often resume its former character. 



The usual gangue in metallic veins is either quartz, calc 

 spar, or heavy spar ; less frequently jluor spar. Calc spai 

 is the gangue of the Rossie lead ore ; heavy spar of much of 

 the lead ore of the Mississippi valley ; fluor spar in some 

 places of the lead of Derbyshire, England. 



Reduction of Ores. — In the reduction of an ore, the object 

 is to obtain the metal in a pure state. It is necessary for 

 this purpose to separate, 1, the gangue ; 2, the impurities or 

 minerals mixed with the ore ; and 3, the ingredient with 

 which the ore is mineralized — as the sulphur, for example, 

 in the common ore of lead. 



1. Much of the gangue will be separated in the process of 

 mining and selecting the ore. Another portion is in many 

 cases removed by pounding the ore coarsely, while a current 

 of water is made to pass over it ; the water carries off the 

 lighter earthy matters and leaves the heavier ore behind. 

 This process is called washing. With a fusible native metal, 

 as bismuth, it is only necessary to heat the pounded ore in 

 crucibles, and the metal flows out. A fusible ore, as gray 

 antimony, is separated from the rock in the same manner. 

 In the case of gold, which is usually in disseminated grains, 

 mercury is mixed with the pounded rock after washing, 

 which unites with the gold ; and thus the gold is dissolved 

 out from the gangue as water dissolves a salt ; b) ■ apoi . 

 izing the solvent, mercury, the gold is afterwards obtained. 



With iron ores, there is no special effort to separate the 

 gangue beyond what is done in the process of mining. 



What is the gangue 1 What is said of the ore in the gangue ? What 

 are the common kinds of gangue 1 What is meant by the reduction of 

 an ore 1 What is necessary for this purpose ? How is the gargua 

 teparated ] How with a fusible metal or ore 1 How with gold? 



