. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. er. Picking Table and Washing Trommel.—After passing throughthe stone-breaker the mineral is roughly classified in a strong washingtrommel, the holes in which may be \ in. diameter or greater, accordingto the class of mineral; the fine stuff which passes through goes ondirect to the roller crushers, but the rougher stuff falls on to the pickingtable, as in fig. 149. The washing trommel should be of exceptionally strong construction,and is best made of boiler plate, with holes d
. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. er. Picking Table and Washing Trommel.—After passing throughthe stone-breaker the mineral is roughly classified in a strong washingtrommel, the holes in which may be \ in. diameter or greater, accordingto the class of mineral; the fine stuff which passes through goes ondirect to the roller crushers, but the rougher stuff falls on to the pickingtable, as in fig. 149. The washing trommel should be of exceptionally strong construction,and is best made of boiler plate, with holes drilled to suit the ore. Itshould be well supplied with a strong stream of clean water, sufficientto thoroughly cleanse the ore. In the case of argillaceous ores, whichare liable to form into clayey balls, a special washing trommel is used,which is referred to in the description of the new mill at the Neuhofi- mine, belonging to the Graf Henckel von Donnersmarck Company-^i near Tarnowitz, in Upper Silesia, on page 446. Notwithstanding the perfection of modern concentrating machinery, THE GATES ROCK-BREAKER. 229. Fig. 148.—Section of Gates Rock-breaker. there can be no two opinions as to the value of carefully hand-pickingthe rich lumps, as well as the sterile pieces of gangue, out of the ore ^qo MACHINERY FOR METALLIFEROUS MINES. before it is crushed too fine, as not only is this the cheapest method,owing to the saving in metal effected through the absence of the losseswhich always occur after crushing, but also it enables the mill to treata greater quantity of crude ore. This applies especially in the case ofrich argentiferous galena, which, owing to its great friability, is apt to make a large proportion ofc slimes on crushing, and this always entails loss ofmineral. The table on whichthis picking is carried outmay either be a rotatingcircular one, as shown infig. 149, around whichstand the women who areusually employed at thiswork, or a long endlesshemp belt running onrol
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