Sor extracting Gold and Silver from other Ores. 29 
on the axis of each barrel, but from which either barrel may be 
detached at pleasure, and its motion stopped without impeding 
the rest. 
Each of these barrels is charged with ten hundred weight of 
the pulverized ore, about three hundred weight of water, and a 
small quantity of sheet-iron, which is added for the purpose of 
decomposing any muriate of silver that may have been formed 
during the process of roasting, and to prevent the subsequent 
formation of any muriate of mercury. 
A gentle rotatory motion is communicated to the bartels for 
about an hour, to mix their contents intimately. Five hundred 
weight of quicksilver is then added to each, and the motion of 
the barrels accelerated to the rate of nearly twenty revolutions 
in a minute, and this is continued for sixteen hours. When by 
assay it is found that the separation of the silver is complete, the 
whole having formed an amalgam with the mercury, and none 
being left in union with the earthy parts or metallic oxides, the 
barrels are entirely filled with water, and they are set in motion 
again for about an hour, but with much less velocity, that the 
amalgam may separate completely from the rest of the mass, 
and be allowed to subside. The amalgam is then drawn off 
from the lowest side of the barrels, and conveyed along wooden 
channels to vessels prepared in another chamber to receive it, 
The remaining water is washed from the barrels into reservoirs. 
The amalgam and surplus mercury, which flow away together, 
are put into leathern bags, which being pressed, suffer the un- 
combined sulphur to passthrough the pores, leaving the amal- 
gam, containing about ont-eighth of its weight of silver, in the 
form of a paste composed of silvery globules. 
‘The washings of the barrels, which are collected in four large 
reservoirs, are kept in a continued agitation, during which the 
mercury which remained entangled with the refuse subsides; and 
as this takes place, the upper strata of the water are successively 
removed till the mercury and amalgam, if any, alone remain. 
This generally occupies about eight hours. This mercury and 
amalgam is of course added to the rest, and from the liquor the 
sulphate of soda is afterwards obtained, 
It remains now to collect the silver which is. thus concen- 
trated in the amalgam, by driving off the mercury. For this 
purpose a furnace of mason-work of a peculiar construction is 
employed. A tripod of iron is placed within it, which standing 
in a vessel of water supports an upright bar of about three feet 
in height, at the upper part of which are arranged five iron sau- 
cers holding portions of the amalgam. The whole of this is 
covered by a bell of cast iron which descends into the water. 
An 
