"24 The Patio and Cazo Process. 



The magistral is the most important reagent employed, and 

 at the same time the cheapest. A little salt, more or less, 

 makes no special difference; but an excess of magistral is always 

 disastrous, and its effects must be attended to at once, or they 

 Avill cause a serious loss of both mercury and silver. The opera- 

 tion of adding the magistral is called incorporo. Whatever 

 magistral is used, it is scattered evenly over the surface with 

 wooden shovels, and then thoroughly incorporated through the 

 pile by digging it in — the operation being called voltear la torta, 

 or turning the pile. When this has been done, another repaso is 

 made, which is repeated every second or third day for about eight 

 hours. The quantity of magistral added varies from one half to 

 two per cent., according to the nature of the ore and the 

 quantity of sulphate of copper contained in it ; more being- 

 required as there are more sulphides. On the supposition 

 that the sulphate of copper alone is of use, about five pounds 

 to the ton of a 35 to 60 ounce ore is required. Generally from six 

 to eight kilos of mercury, azogue, is added for every kilo, of 

 silver contained in the ore in the torta, as determined by the 

 fire assay. The amount of mercury put in at this time varies 

 with the theory of the amalgamator. Some add two-thirds ; 

 others three-fourths of the lowest quantity at once ; others add 

 it in very small quantity at first, and the rest gradually. In any 

 case, the effort is made to add it in the smallest globules possi- 

 ble, by walking over the pile and squeezing the mercury through 

 a canvas bag containing not more than five or six kilograms 

 of it, or through strainers, so as to distribute it as evenly as 

 possible over the pile. 



Immediately after the addition of the quicksilver, the animals 

 are set to treading, the spading being done when they rest. 

 This is continued for two hours. A solution of hot sulphate 

 of copper is then added to the pile ; the quantity being larger 

 as the ore contains sulphur, arsenic, antimony or zinc. For 

 ordinary pure sulphurets, about four kilograms to the ton are 

 used. Precipitated capper, precipitado, in the proportion of 

 one part of coppar to five of sulphate, is also used. This cools 

 the pile. After the sulphate is added, the torta is trodden 

 again until 3 P. M. The mules employed for this purpose do 

 no other work. They are generally blindfolded, and are driven 



