Papers.—1. “Concentration of Ores,”
This paper showed first the necessity for concentrating or dressing metallic ores as a preliminary operation to chemical or metallurgical processes. The various principles made use of were outlined, these being based upon differences in physical properties.
The systems of ore-dressing explained were as follows:—
Water concentration, based upon the action of this fluid upon minerals of different specific gravity.
Magnetic separation, based upon the fact that certain minerals are paramagnetic, whilst others are diamagnetic.
Oil concentration, based upon the power oil has of adhering to certain minerals, whilst other minerals are not affected. Oil, being lighter than water, then rises to the surface, carrying those minerals it adheres to with it.
Flotation processes, in which bubbles of gas are made use of to buoy up certain minerals which are specially attachable to gas-bubbles; other minerals not being so attachable are not buoyed up. The vacuum process, using both oil and gas, was also mentioned.
Electrostatic repulsion process, in which use is made of the fact that mineral particles which are good conductors are instantly repelled when brought into contact with an electrically charged body, whilst non-conductors are not repelled for some time, and may be drawn out of the path they are following.