Flotation of Minerals- 58^ 



most of this gas is generated from gangue particles in the ore, 

 and being more sohible in the liquid than the other gases, col- 

 lects readily on the surface of the sulphides. 



In all experiments with sulphides carbon dioxide was ob- 

 tained on exhaustion. This gas must have been present either 

 in the form of a compound easily decomposed by heating or 

 by reducing the pressure, or as a gas condensed on the sur- 

 faces of the sul^Dhides. and there retained with greater force 

 than other gases present. It was found that the cai'bon 

 dioxide was the last gas to come off. 



The effect of oils. — The effect of oils has long been known 

 in protecting minerals from being wetted by water owing to 

 the oiling of their surfaces, and also the affinity of oils for 

 metals, and many metallic substances. Nearly all the minerals 

 tried could be coated with oil either in the presence or 

 absence of water. This seems to be connected with the- 

 adsorption of gases on the particles themselves, for if the 

 particles are deprived of their gas, then as a rule they do 

 not become coated with oil. It would therefore appear that 

 the oiling of particles is dependent on their gaseous attach- 

 ments. If the particles are oiled to a minute extent, the gases 

 previously adsorbed are retained, and if a solution is heated 

 more gas will become attached to the particles, and flotation 

 will ensue. An oil float may be obtained without acids. 

 jNeai'ly all minerals will, float on water after being oiled. 



The flotation is apparently due partly to the lesser density 

 of the oil and the j^resence of gases adsorbed on the minerals 

 or entangled in the oil. If a large quantity of viscous oil is 

 used gases become entangled in it,, and the product is oily. 

 In course of time the particles will drop away from it, carry- 

 ing' down attached globules of oil. When a lesser amount of 

 cil is used the product becomes a coherent mass like putty, 

 showing no apparent tendency to float. On further decreasing 

 the quantity of oil, the product becomes firmer, and breaks 

 up into rounded pellets. With a still less (juantity of oil, when 

 shaken \\\) with water in presence of air the product becomes 

 flooculent, and increases in volume. This flocculation is due 

 to the adsorption of gases. With very minute quantities of oil 

 the flocculation becomes more pronotuiced, and the tendency to 



