128 THE PROSPECTOR'S HANDBOOK. 



and the silver thrown down from the solution by some 

 metals, such as copper. In the Von Patera method, so 

 largely used in practice, after roasting with salt, the ore is 

 leached with a weak solution of sodium hyposulphite, the 

 silver being afterwards thrown down from this solution by 

 a soluble sulphide. 



In the process whereby the silver-bearing ore is roasted, 

 and a sulphate of silver dissolved by water and the silver 

 precipitated by means of copper, the residue may have to 

 be smelted with addition of gold-bearing pyrites, to obtain 

 a matte in which the gold and silver are retained. 



In the Mexican process, the sorted silver ore (native 

 silver, sulphide, and chloride of silver) is placed in heaps 

 with common salt, for a while, then ground with magistral 

 (derived from roasted iron-and -copper sulphides) and 

 mercury. 



There is no occasion, however, to extend this subject, 

 suffice it to say that the foregoing methods will give an idea 

 as to some of the principles involved. 



The following table will show certain conditions under 

 which the Pan amalgamation and Hyposulphite leaching 

 means are adopted : 



Pan amalgamation { ^ftefroastmg with salt. 



a Direct or after roasting with 



Hyposulphite leaching 



salt. 



Using a mixed solution of 

 copper and sodium hypo- 

 sulphite (Russell's process.) 



Gold from deposits and lodes. 



When the gold is " free " in alluvial deposits, sluices, 

 cradles, &c., washing down of matter by hydraulicing, &c., 

 are made use of. 



When the gold is free in lode matter, the ore is usually 

 stamped very finely, and amalgamation with mercury, as 

 the gold, &c., is washed down inclined planes, &c., the 

 amalgam being eventually squeezed through chamois leather, 

 blankets, canvas, &c,, to get rid of the superfluous mercury, 



