Show colloidal theory of flotation 99 in ill discussing the paper of A F taggart and F B E beach on the flotation process presented at the arizona meeting of the american institute of mining engineers oliverc oliver C ralston of salt lake city has the following to say in the december number of the bulletin this paper has appealed to me as being one of tile the most lucid well connected and complete papers on this subject which has been published to be sure the concepts called upon in an explanation of the flotation process by these authors are mostly old ones which have been more or less discussed in previous literature but they have nevertheless been assembled in a most constructive and suggestive manner we find a new contribution to flotation theory in the effect of fine particles increasing the viscosity of the interfacial film between a liquid and a gas this phenomenon has been variously hinted at but never definitely stated in accepted scientific terms the discussion of contact angles is very clear and will doubtless be welcomed by those who have not had the opportunity to investigate the literature on this subject but it is unfortunate that the of the contact angle observed by sulman and reported some years ago is not mentioned or explained pla ined A few other points need discussion in order to call attention to the fact that while this paper is the best discussion of the subject which has yet appeared all of the truth has not yet been told on page 1385 in discussing the reasons why heating a pulp often allows the recovery of a higher grade froth concentrate four different factors are mentioned one of these factors deemed probable by the authors is that there is an increased number of air bubbles formed by the air released from solution while it is commonly known that heating a solution expels the dissolved air or other gases to one who has seen the great volumes of air that enter the pulp in a flotation machine it is hard to believe that the pitifully small number of additional air bubbles released by heating the solution can have such a good effect I 1 would call attention to the following more probable explanation of this fact the vico sity of water at 80 deg C is less than one fifth of the vico sity at 0 deg C in other words on heating an ore pulp the fluidity of the water in the pulp is very greatly increased and much less water containing entrained gangue will be carried along with the froth during flotation in other words a cleaner concentrate is obtained the surface tension and other physical properties of water are not altered in anywhere near the same degree by change of temperature and I 1 would suggest that the viscosity effect is probably responsible for the major portion of the improvement I 1 notice that in their discussion of the potter delprat process the authors claim to have observed microscopically the condition of the solid particles in the froth and find them completely within the films and at no point in contact with gas the manager of one of the large australian companies using notation flotation told me that two physical chemists in his employ consumed about six months time in an attempt to definitely find out whether the mineral particles were completely submerged in the film or whether they were at some point in contact with gas in ili view of their failure to reach a decision I 1 am inclined to ask the present authors if they are certain of this observation further we notice that electrical forces are not called into question in this discussion of flotation although the authors acknowledge that the potential surface energy in the contact surfaces between dissimilar substances might well include electrical forces which might be called on in explanation of certain aspects of flotation however they feel that once in contact the preferential adhesion to a sulphide surface in the presence of water is sufficient to account for the persistent attachment of the sulphides sulp hides to the bubble films I 1 leel feel that they are justified in this opinion but having seen particles migrate under the microscope when in an electrical field and knowing that the various kinds of particles and bubbles carry electrical charges may I 1 not suggest that the electrical charges assist the various finely divided phases to get in contact the authors consider that mechanical agitation etc is sufficient to get the various phases into contact but the acceptance of these electrical phenomena in noway no way damages the theory which they have presented and merely adds another contributing factor to the theory finally the authors state that they have not appealed to colloidal phenomena in this discussion this statement in the face of the fact that the largest single section of the paper is headed absorption and that most of the forces called upon are those 0 of capillarity is hard to understand while I 1 agree wit with the authors almost entirely in so far as they go I 1 find that their paper is filled with something very closely akin to colloid chemistry the study of ca forces comes under the head of physics and the study of the effect of chemicals on these capillary forces comes under chemical physics or physical chemistry now the physical chemistry dealing with capillary phenomena is known as colloid chemistry and freundlich even went so far as to entitle his text on colloids coll Ka pillar chernie so it can be seen that while I 1 am delighted with the work these authors have done in formulating their theory I 1 am disappointed in the way they have attempted to name it I 1 would say that it can ibe be accepted as part of a colloidal theory of flotation |