58 The Patio and Cazo Process. 



The process which took the place of this* is a very simple one, 

 applicable to all the ores of silver except argentiferous sulphides 

 of copper, galena, or blende, and to ores which contain more than 

 one per cent, of free arsenic, which causes great losses in the 

 mercury. The inventor of it is not known, but it has been in 

 constant use about Copiapo since 1862. 



The ores must be carefully sorted, so as to separate them into 

 different classes, keeping the especially rich ores by themselves, as 

 these are worked much more rapidly than those of lower grade. 

 The difference of time in the treatment of the different ores 

 more than makes up for the trouble it costs. 



The rich ores, including the sulphides, are treated in copper 

 tanks with sulphate of copper, salt and mercury. The solutions 

 are all made by steam, and beforehand, five per cent, of the 

 weight of the mineral being added in salt. The sulphate of cop- 

 per solution is made up to 20° B., and to it salt is added until no 

 more will dissolve. The sulphate of copper is in this way trans- 

 formed into chloride of copper, and the soda to sulphate of soda. 

 When the liquor is saturated, it is decanted into large wooden 

 tanks, and metallic copper, usually old copper sheathing, is put 

 into the liquor, which is heated to ebullition by a current of 

 steam at a pressure of three atmospheres. This causes the cop- 

 per to be attacked, and a sub-chloride of copper is formed which 

 is used in the process. The operation is finished when, by taking 

 about 50 c. c. of the liquor and putting it into a liter of water, 

 the oxychloride precipitates as a white powder, leaving the liquor 

 colorless. The sub-chloride is then formed. The salt requires 

 one vat, the sulphate of copper two, and the sub-chloride one, in 

 their preparation. When the snb-chloride is formed it must be 

 used as soon as possible, to prevent the formation of the oxy- 

 chloride, and in order to do this as far as can be done, the solu- 

 tion is slightly acidulated with sulphuric acid. 



A cast-iron Chilian mill, trapic7ie, each wheel of which weighs 

 four tons, is used for grinding the ores. The bottom of the mill is 

 called solera. This is usually made of cast-iron, but sometimes of 

 steel. The mill turns at the rate of 10 to 12 turns a minute. The 

 ore, which is ground sufficiently fine, is carried off by a current of 



* Revue Universelle des Mines, 1 Series, Vol. 31, p. 493. 



