222 On the Principles Involved in the 



remains. The silver, thus obtained, is not always pure, but often 

 contains gold, lead, copper, bisnauth, &tc. which are separated in the 

 refining operations. 



3. Mexican method of amalgamation. 



The Mexican method, or the amalgamation cold, and in the open 

 air, by means of a mixture of salts, was discovered, in the year 1557, 

 by Bartholomew de Medina, a Mexican miner. This method does 

 not require, that the ores should be roasted, and the only necessary 

 machinery is a stone moving in a circular trough,* and a vertical 

 spindle with arms, revolving in a vat. This method may be em- 

 ployed, where neither water or fuel are abundant. 



The amalgamation shop, is a yard paved with flat flagging stones. 

 The moist schlich or powdered ore, coming from the stone rollers 

 before mentioned, is deposited in forty or fifty piles, ranged circular- 

 ly near each other, so that the circle may be from sixty to ninety feet 

 in diameter. Each heap of schlich contains from fifteen to thirty 

 five quintals in weight, so that when the whole comes to be spread, 

 the mass may be from one and a half to two feet in thickness. Salt 

 is now mingled with the schlich, in a proportion varying from two 

 to twenty per cent.' The mixture is left, for many days, that the salt 

 may dissolve and be equally distributed. If the pyrites are very 

 rapidly decomposed and other chemical changes are evident, the 

 action is diminished by adding lime, or wood ashes, or if the decom- 

 position be very slow, it may be accelerated by adding a mixture of 

 the sulphates of iron and copper, formed by roasting pyritous copper 

 and common pyrites, and exposing them to the weather. 



After some days, mercury is added, in quantities proportioned to 

 the silver in the ore, generally six or eight parts of mercury to one 

 of silver. After a little time, from one to seven per cent, of the mix- 

 ed sulphurets of iron and copper are added, and when the chemical 

 changes begin to take place, which are recognized by the leaden 

 color of the mercury, then, to favor the decomposition and augment the 

 contact, the mass is stirred and moved by mules, oxen, or other ani- 

 mals, walking around in it in circles. This agitation of the mass is 

 continued daily, unless the decompositions should be too rapid, and 

 then the labors are suspended for one or more days, as circumstances 



* The recent superintendent of the mine Valenciana, Mr. John Millington, tells 

 me, that the stones do not roll in the circular trough, but are dragged around. 



