Reduction of Iron and Silver Ores. 221 



so managed, that it shall not become in the least agglutinated or pasty. 

 The ore now goes again through various mechanical operations, to 

 be sure that it may be in a state of minute division. 



It is now ready for the actual process of amalgamation. This 

 is performed in barrels, revolving on an axis by means of machinery. 

 The mixture or charge in each barrel, consists of finely divided 

 roasted ore, mercury, and plates of metallic iron, with sufficient water 

 to make it into semi-fluid paste. 



It is a chemical principle, that when one metal precipitates another, 

 the precipitated one is always in the metallic state, and also, that gold 

 or silver and some other metals, in their nascent state, readily unite 

 with mercury, and form what is called an amalgam. After the bar- 

 rels have received their charges, and are put in motion, chemical 

 changes begin to be effected. The revolution of the barrels tends 

 to bring all the parts of the charge, successively, into contact with 

 each other and with the iron plates. The iron having a strong affin- 

 ity for the chlorine of the chloride of silver, decomposes it, and forms 

 a chloride of iron, which, by solution in the water, becomes a mu- 

 riate. The silver, thus set free, immediately unites with the mercury 

 in contact with it, and forms an amalgam. The mercury, during the 

 revolution of the barrels, is disseminated in small globules through 

 the whole mass, so that as soon as a particle of silver is reduced, it 

 is brought into contact with the mercury. When the barrels have 

 revolved a few hours, with a proper charge of materials, and with a 

 proper velocity, the silver is found to have combined almost entirely 

 with the mercury. If the water be in too great or too small pro- 

 portion, or if the rotation be too rapid or slow, the mercury will not 

 disseminate itself through the mass, so as to effect the separation of 

 silver from the materials with which it is mingled and combined. 

 When the amalgamation is found to be complete, as it generally is at 

 the end of a few hours, the barrels are allowed to stand a short time, 

 that the amalgam may collect in the bottom. The amalgam and 

 mud are then both drawn off and washed, but the washing requires 

 care, lest a portion of the amalgam, which may be still disseminated 

 through the mud, should be washed away and lost. The redundant 

 mercury of the amalgam is removed by pressure applied to leathern 

 bags; the mercury passes through the pores of the leather, and the 

 solid amalgam, having about the consistence of butter, remains. 

 It is next subjected to distillation in proper vessels, by which the 

 mercury is first volatilized and then condensed again, while the silver 



Vol. XXIV.^-No. 2. 29 



