250 MINING INDUSTET. 



these two mills, as given in the table, are among the two extremes of good 

 and bad work. 



No. 9. Varney Pan: Charge of ore 1,200 to 1,400 pounds ; salt, 3 or 4 

 pounds per ton of ore ; sulphate of copper, three-fourths of a pound per ton of 

 ore ; quicksilver 50 pounds, added with each new charge, after the latter has 

 been ground two hours and a half. There is always more or less quicksilver 

 and amalgam remaining in the pan, except just after a clean-up. Steam 

 used direct. Time in pan, four to five hours. In addition to the usual sepa- 

 rator there is a second or supplementary vessel of similar character, the pro- 

 duct of which, though not very important, is returned to the mine. 



No. 10. Wheeler Pans. 



No. 12. Hepburn Pans : Use both salt and sulphate of copper. 



No. 14. Varney Pans : Use both salt and sulphate of copper. 



No. 15. Old-fashioned common pan or tub. The great excess of gold 

 in the return, as referred to the mill sample assay, is probably to be explained 

 by some fault in the assay of that sample, since the return does not differ 

 widely from the general average of other mills when referred to the wagon 

 sample, in which the proportions of gold and silver are about as usual. 



Nos. 16 and 21. Use the Knox pan, an older and simpler form than any 

 of those described in detail in this chapter. 



In judging of the comparative efficiency of various miUs or methods by 

 the results obtained, on a large scale, at any of the miUs in question, it is 

 important to remember that the assay, which is the only standard to which 

 the results are referred, is not infallible. 



Notwithstanding all the care exercised by the parties interested 

 and the great number of samples selected for assay, the result, after aU, is 

 only an approximation to the truth. Some portions of a given parcel of ore 

 may contain free gold or segregated particles of rich silver ore, which quite 

 escape due representation in the sampling, or the contrary may occur and the 

 value of the parcel be thus overestimated. Further, the variable amount of 

 moisture in the ore affects the result, since the assay is of the dried sample. „ 



Finally, the ores produce, in crushing, very variable quantities of slime, • j 



on account, partly, of the character of the gangue, some being more clayey 

 than others, and partly by reason of the varying conditions present in the bat- 



