Flotation of Minerals. 565 



to collect under the surface of the oiled particles in the form 

 of very small bubbles, which collected to form one large bubble, 

 until on becoming too large it broke away and came to the 

 surface, the oil returning to its original form until another 

 large bubble formed from the smaller bubbles collecting to- 

 gether. On adding H\^SOj^ many bubbles and apparently the 

 excess of the oil left the minerals, and on standing or on heat- 

 ing, the minerals, tjiuirtz, calcite. and gypsum became practi- 

 cally free from bubbles. The sulphides, metals and garnet still 

 had the bubbles collected on them, but in a different form, each 

 bubble being separate, and not combining with the others to 

 form one large bubble under the surface of the oil as was the 

 case with water alone. 



A very small amount of oil only is required to oil a consider- 

 able amount of any mineral. Some South Mine tailings weigh- 

 ing 20 gms. was added to water, and 1 drop (.0'26 gms.) oleic 

 acid added and the mixture shaken up, and put in a vacuum 

 flask. On reducing the pressure the whole product, metallic 

 and non-metallic, floated to the surface. With 40 gms. only 

 about half was raised. 



In Alkaline Solutions. 



On the surface. — Most minerals will float on the surface of 

 an NaOH solution, but for a few moments only, and then 

 become wetted and sink. 



On heating. — When heated in a solution of XaOH, the 

 minerals will not float. On adding an ammonium salt, al- 

 though gas is given ofl", no float takes place. With some zinc 

 concentrates that have been previously floated, a good float 

 was obtained in an ammonium carbonate solution. With 

 NH4CI a partial and non-selective float was caused. Oleic acid 

 saponified with ammonia will cause non-selective flotation, and 

 on adding H^SO^ till acid, the silicates will sink, and the sul- 

 phides remain floating. A sample of zinc concentrates would 

 not float in NaOH, and on addition of Hg SO4 till acid would 

 only float after heating for a considerable time. 



Under reduced pressure. — Bubbles formed on the minerals 

 under an NaOH solution under reduced pressure, the solution 



