Flotatioi) of Minerals. 581 



Summary. 



Adxiir ptiDii of Ga,sts. 

 All minerals adsorb gases. 

 Sulphides appear to naturally absorb CO^. 

 The consequence of this is — 



(1) Particles aiv not wholly wetted when immersed in water. 



(2) Particles also tend to float when sprinkled on the 



surface. 



(3) When immersed in water and heated, the air or gases 



disolved in water will collect on the particles, and 

 float or tend to float them to the surface. 

 (i) Saturated solutions of gases in water evolve gas which 

 collects on all particles. 

 The addition of acids. — ^Metallic particles, such as sulphides 

 and metals, when innnersed in dilute acid solution, are not 

 wholly wetted, but particles of rock materials become more 

 readily wetted, and give off their adsorbed gas. When different 

 diy minerals are sprinkled on the surface of dilute cold acid, 

 the tendency for them all is to float as in water. The minerals 

 are more readily wetted by hot acid solutions than cold. 



T/ie addition of alkali^. — When different mineral particles 

 are immersed in an alkaline solution, they tend to part with 

 their adsorbed gases, and will not float even when heated. 

 When sprinkled dry on to the surface of the solution, they re- 

 main for a few seconds only, and then break through. 



Flotation of SuIpJtides. 



This is due to the property possessed by minerals of collect- 

 ing gases on their surface, in such quantity as to diminish the 

 density of the product, to less than that of the liquid. By 

 calculation from the decrease in density it is found that the 

 amount collected on dry sulphides is sometimes half the 

 volume necessary to float them at ordinary temperature. 

 Given a starting point, any gas generated in or introduced 

 into the solution will tend to collect on the surface of the 

 particles. If acid is added, the gases Avill leave the gangue 

 particles and collect on the sulphides ; the latter, therefore, 

 tend to float and the former to remain under the surface of 



