The Patio and Cazo Process. 35 



salt, or to cold. If, on examining the black sulphurets, poluillos, 

 and nibbing the small metallic globules of mercury or amalgam 

 found among them with the ringer, they unite to a large glob- 

 ule, the pile is nearly finished. If they yield a dry amalgam, 

 it is not. The best way to ascertain this, is to make a fire assay 

 of the original pulp and of the torta, and to judge by the yield. 

 When the ores contain galena and blende, these substances de- 

 compose the chloride of copper, and the sulphur goes to the cop- 

 per. The proportion of magistral to be added must, therefore, be 

 largely increased, notwithstanding the fact that the loss in silver 

 is always greater when there is an excess. 



When the amalgamation is complete, a considerable quantity of 

 mercury, in addition to that required for the amalgamation of the 

 silver, is added, with theobjtctof making sure the collection of all 

 the mercuiy and amalgam. In some districts this additional 

 mercury is called bono, The pile is still trodden for some time. 

 This last addition of mercury has for its effect to make 

 the amalgam a little more fluid, so that it may be collected 

 more easily, and to collect the floured mercury which would 

 not be caught in the subsequent washing, and to prevent as far 

 as possible further action of the reagents on the amalgam. 



There is always a loss of mercury equal in weight to that of the 

 silver contained in the ore. A further loss of from 7 to 10 per 

 cent, comes from that which is mechanic illy carried off either in 

 the patio or in the washing. With such oivs, 40 per cent, of the 

 silver is often lost. Tiie loss of mercury is often from 100 to 

 200 per cent, of the weight of the silver obtained. As a mean it 

 is from 140 to 160 per cent, or 7 or 8 times the loss in the Frei- 

 berg barrel amalgamation process. The attempt was made to 

 diminish this loss by adding a little iron, but in order that the 

 effVct may be sensibly felt, a large amount must be used, which 

 increases the expense and does not diminish the loss much. In 

 some of the works the mercury is replaced by an amalgam con- 

 taining 30 per cent, of capper, which reduces the loss materi- 

 ally. The effect of the copper is the same as that of the balls of 

 copper or iron which are used in the Freiberg barrel amalga- 

 mation process. Too much copper, however, must not be added, 

 or it would make the amalgam of silver too friable. The loss in 

 silver is increased by this method, but the loss in mercury is re- 

 duced to 1^0 to 150 per cent. The attempt was also made to use 



