42 The Patio and Cazo Process. 



into a large trough, originally always of stone, but now often 

 made of iron. When the whole has been collected, a large 

 amount of mercury, usually ten to fifteen per cent, of the quan- 

 tity of quicksilver used in the arrastra, is added to the amalgam 

 in order to clean it. It is covered with water to prevent splash- 

 ing, and carefully worked over. Whatever impurities rise to 

 the surface are removed w T ith a cloth, and fresh water is again 

 added. This operation is repeated until the surface becomes 

 and remains bright. The amalgam is dried and weighed, and 

 is then put into a conical canvas bag, like those used in the 

 West, which is called manga, set over a receptacle made of 

 hide, pila, to catch the drippings, which, as they contain some 

 little silver, are of more value in the next charge than pure 

 mercury. This is put into flasks for preservation. The amal- 

 gam, free from every thing except mercury, copella, after hanging 

 several hours, is ready for retorting. 



At Chihuahua,* where very rich ores of native silver are 

 treated, the amalgam looks like a coarse sand, but by the ad- 

 dition of mercury the dirt is removed from it. This dirt, how- 

 ever, is very rich, and is further concentrated. When par- 

 ticularly pure silver is required, it is carefully washed, and 

 ground on a stone, in order to remove the sulphide of silver ; the 

 result is a very pure amalgam, which yields silver purer than fine 

 bars. The amalgam cleaned with mercury is strained in canvas 

 cloths, and the quicksilver pressed out into small balls 0.05 m. to 

 0.06 m. in diameter, by rubbing them with the hands. This is 

 the only way they have been able to get very high grade silver. 



Formerly, all the amalgam was beaten and pressed into an 

 iron mould, to make bricks of amalgam, hollos, of such a shape 

 that when six were placed together they formed a circular 

 cake with a round hole in the centre. One ton of these 

 was piled on iron supports, over a stone tank filled with water 

 to nearly the top of a copper or iron bell, capellina,\ which is 

 0.90 m. high, and 0.45 m. in diameter. This left a space 

 0.02 m. between the amalgam and the bell which was low- 

 ered to its place by pulleys. A wall of adobes, leaving a 



* Mining Commissioners' Report, 1872, p. 437. 

 f Annales des Mines, Vol. 20, PI. 2, Fig. 2. 



