Flotation of Minerals, Part II. 32 3 



derived from the decomposition of carbonates during the experi- 

 ment is shown by the negative results shown by cerussite and 

 calcite. 



These results indicate that there is apparently a concentra- 

 tion or condensation of gas consisting mainly of carbon dioxide 

 on the surface of the sulphides, and to a much less extent on 

 the other minerals tried. This gas is held persistently, and 

 does not obey the laws of gaseous diffusion, and may therefore 

 be present in the liquid form. This is indicated by the fact 

 that it is the more easily condensed gas, that is the more per- 

 sistently attached. The fact that finely divided material in 

 the form of slimes will attach more gas than similar material 

 in a coarser state, indicates that the action is a surface action. 

 It may be akin to the action of charcoal, which Avill absorb 

 large volumes of the more readily condensible gases as carbon 

 dioxide, sulphur dioxide, and ammonia. It is known that 

 water vapour will cling most persistently to some surfaces even 

 at high temperatures.^ 



In a previous paper already referred to, the writer found that 

 carbon dioxide was obtained from all the sulphides tried by 

 the aid of heat and exhaustion in the presence of water. It is 

 probable that the gas film can only be expanded for removal 

 in appreciable quantities in the presence of water, and that 

 exhaustion in the dry state does not remove all the gas present. 

 The film can be removed by solvents. 



The thickness of the film is probably analogous to the thick- 

 ness of adsorbed oil and adsorbed water films. 



Analogy of gas adsorptions with oil adsorptions. 



When an excess of oil is attached to a sulphide it can be 

 separated to some extent by stirring or by pressure. Simi- 

 larly if a sulphide fiotation product, which was floated by gas, 

 is stirred, a large proportion of the excess gas is given off. 

 This can be seen by the larger bubbles bursting, and the 

 shrinkage in volume of the flotation product on standing. If a 



1 "Adsorption of water vapour by quartz." .Journal of Phys. Chem., vol. 

 page 617. 



