Fig. 15. Stone-Breaker (Sectional View).
The Grusonwerk Ball Mills [(Fig. 16)], made by Krupp of Germany, as also that made by the Austral Otis Company, Melbourne, are fast and excellent triturating appliances for either wet or dry working, but are specially suitable only for ores when the gold is fine and evenly distributed in the stone. The trituration is effected by revolving the stone in a large cylinder together with a number of steel balls of various sizes, the attrition of which with the rock quickly grinds it to powder of any required degree of fineness.
Fig. 16. Grusonwerk Ball Mill.
Probably more mines have been ruined by bad mill management than by bad mining, though every experienced man must have seen in his time many most flagrant instances of bungling in the latter respect. Shafts are often sunk on the wrong side of the lode or too near or too far away therefrom, while instances have not been wanting where the (mis)manager has, after sinking his shaft, driven in the opposite direction to that where the lode should be found.
A common error is that of erecting machinery before there is sufficient ore in sight to make it certain that enough can be provided to keep the plant going. In mines at a distance from the centre of management it is almost impossible to check mistakes of this description, caused by the ignorance or over sanguineness of the mine superintendent, and they are often as disastrous as they are indefensible. Another fertile source of failure is the craze for experimenting with untried inventions, alleged to be improvements on well-known methods.
A rule in the most scientific of card games, whist, is “when in doubt lead trumps.” It might be paraphrased for mining thus: “When in doubt about machinery use that which has been proved.” Let some one else do the experimenting.
