GOLD. 321 



the bulk of sand is thus reduced to a manageable quantity 

 the gold is amalgamated with clean mercury ; the amalgam 

 is next strained to separate any excess of mercury, and final- 

 ly is heated and the mercury expelled, leaving the gold. In 

 this way by successive trials with the rock, the proportion 

 of gold is quite accurately ascertained. It is the same pro- 

 cess used with the larger washings, though on a small scale. 

 Mercury unites readily with gold, and thus separates it from 

 any associated rock or sand ; and it is employed in all exten 

 sive gold minings, though much gold may be often obtained 

 by simple washing without amalgamation. 



The operation of hand washing is called in Virginia pan- 

 ning. With a small iron pan, they wash the earth in a tub or 

 in some brook, and thus extract much gold from the gravel or 

 soil, which is said to pan well or pan poorly according to the 

 result. Masses of quartz, with no external indications of 

 gold, examined in the above way at a Virginia mine, afford- 

 ed an average of more than eight dollars to the bushel of 

 gold rock. 



When gold is alloyed with copper or silver, the mode of 

 assay for separating the copper depends on the process of 

 cupellation ; and that for separating the silver, on the 

 power of nitric acid to dissolve silver without acting on the 

 gold. 



The process of cupellation consists in heating the assay 

 in a small cup (called a cupel,) made of bone ashes, (or in 

 a cavity containing bone ashes,) while the atmosphere has 

 free access. The heated metal is oxydated by the air pass- 

 ing over it, and the oxyd formed sinks into the porous cup, 



1 leaving the precious metal ^ 



behind. The shape of the /^E^^\V\jK\V^\ 

 cupel is shown in fig. 1. In 



order to fuse the alloy and liB 

 still have the atmosphere 



circulating over it, the cupel is placed in a small oven-shaped 

 vessel, called a muffle (fig. 2 :) it is of infusible stone ware, 

 and has a number of oblong holes, through which to admit 

 the flame from the fire, and give exit to the atmosphere 

 which passes into it. The muffle is inserted in a hole fitting 

 it in the side of a vertical furnace, with the open mouth out 



How is a rock examined for gold ? What are the processes for sepa 

 rating gold from silver or copper ? Describe the process of cimellatioa 



27* 



