280 MEsriNG INDUSTRY. 



frequently tested by means of a thermometer plunged into the pan. A tem- 

 perature of 185° Fahr. was found to act most advantageously. The pan worked 

 well; the grmdmg action was perfectly satisfactory; the ore being kept in a 

 constant and rapid circulation, and the mercury finely disseminated through 

 the entire mass. The muller made 118 revolutions per minute. 



The operation concluded, the pulp was drawn off into the settler, the pan 

 thoroughly washed out, or "cleaned up," and every particle of amalgam re- 

 moved. 



An additional quantity of mercury was placed in the settler, and water 

 poured in until it was about half full. The stirrers made 30 revolutions per 

 minute. The pulp was withdrawn at the end of four hours. The water, and 

 the very lightest material, was allowed to escape, but the great bulk of sand 

 and mercury was collected together in buckets and separated by hand, to avoid 

 all loss. In washing, the tailings were made to fall upon a slightly inclined 

 table, or trough, so that, if by any accident, mercury went over it could be 

 easily recovered. 



The quicksilver after being washed free from sand was strained through 

 buckskin, and the amalgam collected for retorting. The difference in weight 

 between the mercury used in the pan and settler and that which remained at 

 the conclusion of a charge, after adding the amount retained in the bullion, 

 was, in most cases, scarcely appreciable. Owing to the well-known property 

 of mercury to retain a small portion of silver in solution, which the ordinary 

 pressure used in separating the bullion fails to recover, the precaution was 

 taken to have it all previously primed or charged before adding it to the pan. 

 This was accomplished by allowing the mercury and metallic silver to stand in 

 contact for some time, and then straining off the amalgam formed. 



The amalgam obtained from each experiment was weighed and put sep- 

 arately in small sheet-iron cups. The number of each charge being stamped 

 plainly on the iron, several of them were then placed together, on the bottom 

 of a small cast-iron retort, and the mercury distilled over. After the retort 

 had cooled down the remaining bullion was taken out and accurately weighed. 

 Careful assays of each lot were made, and always conducted with proofs, and 

 the metals separated by nitric acid in the usual way. 



I 



