The Pul in and Cazo Process. 59 



water, the quantity of which is regulated according to the fine- 

 ness to which the ore is to be ground. This water is made to 

 pass through slime-pits five meters by two meters, and one 

 meter 'deep, enough to run off perfectly clear from the last one. 

 When one of the tanks is full, the stream is turned on to another. 

 The full one is left for 8 to 10 hours. The clear water is then 

 drawn off, and the pulp thrown out with shovels upon an area 

 called canclia, to dry. When the ore is sufficiently dry, it is 

 charged into barrels similar to the Freiberg amalgamation bar- 

 rels. They are of different sizes, their capacity being from one 

 to four tons, the larger the better. Those which hold four tons 

 are 1.80 m. by 1.50, with a thickness of stave of 0.075 m. To 

 the four tons of ore, enough of the salt solution is added to form 

 a thick mud. The quantity of magistral to be added depends on 

 the kind of gangue, much more being required for carbonate of 

 lime than for clay or oxide of iron, as the former decomposes 

 the sub-chloride. For an ore of about $80 to the ton, and a 

 variable gangue, 28 to 30 litres of the magistral are added. 

 The barrels are turned from twenty minutes to half an hour 

 to make the mud quite uniform. Mercury amounting to from 

 20 to 25 times the quantity of silver contained, is then added. 

 If there is a large amount of chloride or bromide of silver in the 

 ore, twenty-five per cent of the weight of the silver contents of 

 the ore is added in lead. This is amalgamated with mercury 

 before it is introduced, and has for its object to prevent the for- 

 mation of chloride and bromide of mercury, and a consequent 

 loss. Lead is very easily attacked by the chlorine and bromine 

 set free — much more easily than mercury. This saves the 

 the mercury from being lost as chloride, and also prevents a me- 

 chanical loss, as the chloride of mercury, once formed, envelops 

 the globules of mercury and prevents both their coming together 

 in a mass and their action on the silver. Besides this, the mer- 

 cury is much more easily reduced to a powder by this means, and 

 is kept so, causing a great loss. This simple device of using lead 

 reduced the loss in mercury, when the chloride and bromide ores 

 were used, from 150 per cent, to 25 per cent. As soon as 

 the mercury is introduced, the barrels are turned at the rate of 

 four to five turns a minute for six hours. The operation is then 

 complete. Water is added in considerable quantities, the barrel 



