584 Keimetk A. Miclde: 



float becomes greater. These results may be obtained with 

 gangue and metallic substances. Gases collect more readily 

 on oiled than on unoiled particles. 



The effects of acids on oiled particles. — The addition of acid 

 causes a more selective action. If oiled gangue and metallic 

 particles are immersed in water, and acid is added, then the 

 oil will tend to leave the gangue particles and become attached 

 to the sulphides. The action of the oil in this respect is simi- 

 lar to that of the gases attached to different minerals, and 

 probably is due to the same cause. 



If an ore is treated with an acid and the acid is removed, 

 then if the particles are oiled, the oil tends to become attached 

 to the sulphides only. This is probably due to the removal of 

 the gas from the gangue, which prevents oiling of the same. 

 If acid and oil are added together, the action of the oil is 

 selective, as in the previous case. The presence of oil on their 

 surface does not prevent the minerals being attacked by acids. 



The amount of acid required for selective flotation depends 

 on the composition of the ore, the temperature and the pres- 

 sure existing at the time. Generally it may be stated that an 

 increase of acid will give a purer sulphide product, but flotation 

 will take place at a lower temperature, and with a lesser 

 amount of acid, with oil and acid than with acid alone. A 

 selective flotation can be obtained in some cases by treatment 

 with a chlorine solution previous to the addition of oil, and 

 without the addition of acid. 



Some of the light volatile oils will cause flotation in an acid 

 solution at a low-er temperature than the heavier and thicker 

 oils. With some Broken Hill tailings a flotation takes place at 

 ordinary temperature with sulphuric .acid and a volatile oil. 



Effects of oils and aUalis. — Flotation can be obtained in 

 alkaline solutions when oil is used, but in every case tried the 

 action was non-selective. On making the solution acid the 

 action becomes selective, only the sulphides floating. 



The flotation of mineral particles appears then to depend 

 on the particles having gas attached to them becoming en- 

 tangled, or caught, by the surface film of a liquid. This film 

 may be (1) the free surface of a liquid, (2) the surface of a 



