50 The Patio and Cazo Process. 



associated as they usually are with highly oxidized substances* 

 The presence of much sulphide renders the losses large. The 

 process becomes difficult with the arsenio and antimonio sul- 

 phides, and impossible when there is much galena, blende, 

 tetrahedrite, or bournonite in the ores. Not the least of the dis- 

 advantages of the process is the facility with which other people 

 than the owners may make a clean-up, the only protection against 

 this being the difficulty of selling unrefined silver, especially in 

 small quantities. In very large works where much capital is in- 

 vested, the item of time is a matter of consequence, but there 

 seems to be no other process possible until transportation shall 

 become less difficult. 



THE CAZO PROCESS. 



There seems to be no doubt that the patio process was in use 

 in South America up to about the commencement of this cen- 

 tury. It was still used there, to a very limited extent, until 

 the year 1830, at which time it seems to have been quite generally 

 given up, probably on account of the very large quantity of negros 

 or sulphurous ores which began to be found. It was replaced 

 in part by the Cazo, or caldron method, which is still in use 

 there, and in some parts of Mexico, and partly by a new method 

 in which the copper bottom was replaced by an iron one, and 

 finally by still another process, which, while it imitated the pan 

 amalgamation method so far as the machinery was concerned, 

 added the chemicals which were supposed to form in the Patio 

 already prepared. We shall briefly describe all these processes. 



The Cazo process was invented in Chili, in the year 1609,* 

 by a priest, Albaro Alonzo Barba, who, in his description of his 

 own process, insists that the vessel in which the w r ork is done 

 should be made entirely of copper, though this was long since 

 found not to be necessary. The ores to which this method is 

 applied are the rich surface ores — chlorides, bromides and iodides, 

 which, if they are not rich enough, must be concentrated on the 

 jilanilla. The process yielded nearly the whole of the silver which 

 is in them. The loss in mercury is from twice to tw T o and a 

 half times the total quantity of silver contained. The ojDeration 



* Percy's Metallurgy of Gold and Silver, Part I, p. 656. 



