Reduction of Iron and Silver Ores. 223 



may require.* The labors are continued until the amalgamation is 

 found to be completed, and this often requires from two to five months, 

 unless the climate should be a very vi^arm one. It may be doubted 

 whether this method of amalgamation would succeed in this climate 

 without artificial heat. 



The mud, containing the amalgam, is now thrown into vats, in which 

 is placed a revolving vertical shaft, with arms. A stream of water 

 runs into and from the vat, and the arms of the shaft, by their motion, 

 keep the earthy particles in suspension, which gradually flow off with 

 the water, while the amalgam collects at the bottom. The excess 

 of mercury is separated, by pressing the amalgam in leathern bags, 

 through the pores of which the mercury passes, leaving a semi-solid 

 amalgam. 



The silver is obtained from this amalgam, by the same operations 

 as in the Saxon method of amalgamation. 



4. Amalgamation hot, by means of copper. 



This consists in heating the powdered ores with mercury in cop- 

 per vessels. It was first proposed in 1590 by Alonzo Barba. It is 

 employed principally for amalgamating the earthy ferruginous ores of 

 silver, called pacos and colorados, and for those ores which contain 

 much muriate of silver. 



The ebullition favors the operation, the copper tends to decom- 

 pose the muriate of silver, and the loss of mercury is very small. 

 Iron vessels would probably be as effectual as copper, and would be 

 far more economical. 



5. Loss of Mercury. 



In the Mexican method of amalgamation, the loss of mercury is 

 from 1.4 to 1.7 parts of mercury for one part of silver obtained ; in 

 the Saxon, not to exceed one of mercury to five of silver, so that by 

 the Mexican method, the loss of mercury is more than seven times 

 as great as when the Saxon method is employed. By the Mexican 

 method, the loss of mercury forms more than one fourth of the whole 

 expense of amalgamation. 



The loss of mercury may be accounted for, 



* Sometimes, the mere cessation of labor is not sufficient to diminish the chemical 

 action to a proper degree, and then lime or wood ashes is added. Sometimes, it is 

 also necessary to quicken the chemical action, and then, the mixture of sulphate of 

 copper and iron with peroxide of iron, called magistral is added. 



