54 The Patio and Cazo Process. 



i 

 ceed 25 per cent., and whatever maybe the necessity for it, the 



number of turns of the muller will hardly exceed ten. About 



half the weight of silver contained in the ore is then' added in 



mercury, and the mullers set in motion at the rate of ten turns 



per minute. The amalgamation commences at once. At the end 



of an hour an assay is taken from the bottom, taking care to 



take it ahead of the muller. If the amalgam washed out looks 



like light grey sand, it is composed of two of mercury for one of 



silver; the same quantity of mercury is again added, and at the 



end of an hour another assay is made, and so on, until the 



amalgam, even after it has been worked in the fondou for half 



an hour, shows an excess of mercury. The priieva en crudo is 



then made, and if any ore is found, the operation is continued 



half an hour without any addition of mercury. At the end of 



six honrs the operation will generally be finished. 



If there is an excess of mercury, there is danger that the 

 sides of the vessel will be attacked; if there is no excess, 

 but if the velocity of the muller is decreased, the copper 

 and mercury become alloyed, and the bottom of the fondon be- 

 comes coated with a very thin coating of silver amalgam which 

 is very difficult to remove. As the copper surface is much di- 

 minished, the operation is very considerably lengthened. There 

 is also danger that the mercury will flour, and the loss in silver 

 will be very great. There is only one remedy for this, which is 

 to empty the fondon, and scrape the bottom clean. It is very easy 

 to prevent this accident by adding the mercury carefully and in 

 small quantities at a time, and by keeping up a uniform but 

 rapid motion of the mullers. With these precautions the work 

 is very nearly independent of the skill and intelligence of the 

 men. The results are quite uniform, and are obtained in a very 

 short time. 



As the reactions are not performed at the expense of 

 the mercury, there is no occasion for any loss of it. If the 

 operation is well carried out, all the mercury used should 

 be collected at the end of the process ; but this is never 

 done. Some of it is floured, some of it volatilized, so that the 

 loss is counted at about two per cent. The reason why there is 

 such a small loss probably is that the work is done hot. The 

 loss in silver is variable. The ores almost always contain sul- 



