CHEMISTET OF THE WASHOE PEOCESS. 289 



of mercury, and at the same time is very rapidly absorbed when the two metals 

 are brought into contact. Sulphate of copper possesses, to a certain extent, 

 the property of expelling lead from mercury, copper being amalgamated and sul- 

 phate of lead formed at the expense of the sulphuric acid of the copper salt. 



If a concentrated solution of sulphate of copper be allowed to stand upon 

 lead-amalgam the action takes place quite rapidly, mercury containing lead act- 

 ing much more energetically upon the copper solution than when perfectly pure. 



This salt, however, does not appear, under any circumstances, to possess 

 the power of completely driving out the lead. 



Another advantage derived from the addition of a small quantity of the 

 sulphate of copper is that mercury, under certain conditions, when exposed to 

 the solution, forms a minute amount of copper-amalgam, which causes the 

 metal to act with a somewhat greater intensity in the decomposition of the sil- 

 ver sulphide than when perfectly pure. 



Iron, as a reducing agent, in the pan process, probably plays an important 

 part in bringing about the favorable results obtained. This may occur in three 

 ways: 



First, It aids, in a great measure, the decomposition of the chloride ot 

 silver. 



Secondly. It reduces the calomel formed during the operation ; the chlorine, 

 combining with the iron, goes into solution, and the heavy metal is liberated. 

 In this way it not only prevents a chemical loss of mercury but also serves to 

 keep the surface of that metal bright and clean, which otherwise might be 

 coated with a thin film of sub -chloride, which would greatly destroy its activity. 



Thirdly. It undoubtedly assists directly in the amalgamation, where the two 

 metals are brought into close contact with the easily reducible sulphurets. The 

 successful and continued operations in Washoe, without the aid of any other 

 chemical agents, sufficiently prove this statement. The experiments already 

 cited in treating argentite and iron filings with mercury confirm the fact. 



Humboldt, in speaking of the amalgamation problem in Mexico, draws 

 attention to this point and remarks upon the rapidity with which amalgama- 

 tion was secured when the two metals were triturated together with argentite. 

 This action of iron is obtained not only from the constant agitation maintained, 



which brings the pulp and metal in contact with the sides and bottom of the 

 37 



