pulverised in from four to six months, but it is better to expose it for a longer period, even for a whole year.
Washing and Concentrating Machinery
After the blue ground has been weathered for a sufficient time, it is again loaded into trucks and hauled to the crushing machinery (Fig. 8). The first or "comet" crushers reduce the ground so that it will pass into hoppers and thence into revolving cylinders covered with perforated steel plates, having holes i|- inches in diameter which separate the finely crushed from the coarse pieces.
Pieces larger than ij inches pass out of the end of the cylinders and fall upon a conveyor belt, which takes them to the end of the machine these pieces are mostly waste rock which is found in the blue ground.
The fine ground which passes through the holes in the cylinder, together with a plentiful current of water, flows into the washing pans. These pans are of iron,