SILVER 



805 



pyrites, or sulphide of copper and iron, pulverised and calcined, -which converts it into 

 a sulphate. About 25 Ibs. of this magistral are added for every ton of ore in the torta, 

 and the mules are again put in, and tread the mass for several hours. Chemical action 

 now commences : the salt, magistral and metallic sulphurets are decomposed, and new 

 combinations are in progress. Quicksilver is then introduced, being spread over the 

 torta in very small particles, which is effected by passing it through a coarse cloth. 

 Tho quantity required is six times the estimated weight of the silver contained in the 

 ore, or 3 Ibs. for every marc of 8 ozs. 



The quicksilver being spread over the surface, the mules are once more put in, and 

 tread the whole until it is well mixed. This treading is called the repaso, and is 

 repeated every other day, or less often, according to the judgment of the azoguero or 

 superintendent, until the operation is completed. 



But it is in the progress of the operation that the skill of the azoguero is most 

 required, because he must attend to certain signs or appearances which present them- 

 selves to him, and upon which depends the success of his work, whether as it regards 

 the produce of silver or the economy of quicksilver and other materials and time. 

 For this purpose he has a small quantity of the torta put on one side, upon which he 

 operates before adding materials to the torta itself; this is called a guia, or guide. 



In order to ascertain how the chemical action in the torta proceeds, he collects a 

 small quantity of the slime and washes it in a small bowl, and by the signs presented 

 by the quicksilver and amalgam he, from his practical knowledge of the subject, is 

 able to judge as to the state of the torta ; whether it requires more magistral or 

 quicksilver; or whether it has had too much magistral, in which case it is hot, and a 

 little lime must be put in to decompose the excess of chloride of copper. This 

 simple plan is termed the tentadura, by which in fact the azoguero is guided through- 

 out the amalgamation process. 



When at length he finds the quicksilver is no longer absorbed, the operation is 

 considered complete, and the torta rendida,OT ready to be washed, and sometimes lime 

 is added to stop further action. A large quantity of quicksilver is then thrown in, and 

 is called cl bano, or bath, which combining with the amalgam, causes it to separate the 

 more readily from the slime in the washing. Tho time required to complete the pro- 

 cess varies from ten to thirty days ; but in some places is often considerably more, 

 according to climate and the nature of the ore. 



The amalgam has now to be separated from the mass, which is done at Real del 

 Monte by washing it in a large square vat, in which several men keep constantly 



