22 The Patio and Cazo Process. 



sulphate that it did before. This is owing to the fact that the 

 tradition has indicated that the ore must be roasted with salt, 

 which in this case, at least, is not only useless, but is a harmful 

 condition. When copper ores containing sulphur are not found, 

 but other copper ores are, these are roasted with the addition of 

 iron pyrites for the purpose of making the sulphate of copper. 

 When there are no ores of copper, roasted iron pyrites alone is 

 sometimes used.* Laur cites the following experiments : — 



Two tortas of ores easily amalgamated were made and treated 

 in exactly the same way, and at the same time. The piles were 

 composed as given below : — 





Sulpha te of Copper. 



Sulphate of Iron 





Torta. 



Torta. 



Dry Ore, 



2,000 kilos. 



2,000 kilos. 



Salt, 



105 



105 



Sulphate of Copper, 



6 







" of Iron, - 





6 



Mercury, 



12 



12 



Water, - 



700 



700 



Each torta contained 2,2-10 grams of silver. After 18 days, 

 during which time it was necessary to add 16 grams of mercury 

 to each of the piles, each torta was washed separately, and the 

 amalgam collected and distilled, with the following result: — 



Silver collected in the sulphate of copper torta, - - 1,890 grams. 



iron torta ■ - - 780 



Loss in silver in the sulphate of copper torta, - - 15.6 per cent. 



" " " iron torta - - 65 " 



This explains sufficiently well why sulphate of copper is pre- 

 ferred, although the losses in such experiments, made in a very 

 small way, are much more than they would be in a large torta. 

 But even supposing that the loss is reduced to ten per ceut., 

 with sulphate of copper used in a large way, the loss by the use 

 of sulphate of iron would still be 41.6 per cent. 



In Chili and Peru,f considerable quantities of sulphate of 



* Annales des Mines, 6th Series, Vol. 20, p. 262. 

 f Berg und HiUtenrnannische Zeitung, 1881, p. 302. 



