582 Kenveth A. Miclde: 



the liquid. When substances in the solution, such as car- 

 bonates, are attacked by acids, the gases evolved saturate teh 

 liquid, and commence to grow on the sulphides. Sulphuretted 

 hydrogen, steam, air, and any Qther gases present either in the 

 solution, introduced into it, or evolved from the minerals pre- 

 sent, assist flotation, provided the sulphide pai'ticles have diy 

 points on them for the gases to become attached to. Some 

 sulphides naturally adsorb gases, and such sulphides readily 

 float. The bulk of Broken Hill ores may be taken as examples. 

 Other ores require preliminary treatment, so as to alter their 

 surface to some extent. This may be done in certain cases 

 by merely heating to 250 deg. C, or immersing in some solu- 

 tion which will attack the sulphides, such as nitric acid or 

 chlorine solution. Sulphides which condense or adsorb gases 

 well will gather together in a solution as flocculent masses, 

 while those that do not, remain individually distinct, like 

 grains of sand. 



In certain cases sulphides will tloat in acid solution at 

 ordinary temperature, but for the most part with dilute acid 

 solution, flotation starts at about 80 deg. C. The explanation 

 put forward that flotation at that temperature is due to cer- 

 tain carbonates, such as rhodochrosite, siderite, smithsonite 

 being attacked and giving off COj, does not appear to be cor- 

 rect, for under reduced pressure these minerals are attacked 

 but flotation does not take place. The presence of silicic acid 

 and sulphui', as stated by De Bavay as necessary for a coagu- 

 lum, is not necessary in many cases of successful flotation. 

 When minerals are treated with dilute acids, and then exposed 

 to the air, certain sulphides adsorb gases on their surface. If 

 they are alternately wetted and exposed to the air, they will 

 become entrapped by the surface film of water which they are 

 brought in contact with. The appearance of the film is the 

 same as that of a bubble of gas under the surface of a solution 

 wuth sulphides attached. The sulphides in both cases adhere 

 to the surface film of the bubble or free surface of the liquid. 

 but are mainly below the surface itself. The gas obtained in 

 all cases from experimental work and also from samples ob- 

 tained from various flotation plants was CO^, . with varying 

 quantities of nitrogen and oxygen. There is no doubt that 



