276 REPORTS ON THE STATE OF SCIENCE, ETC. 



The C oncentrotion of Minerals by Flotation. By Edwin Edser, A.R.C.Sc, 

 iF.Ph.S., F.Inst.P. (Minerals Separation, Ltd., London). 



The fundamental scientific principles underlying the flotation of minerals 

 are treated in detail — e.g. surface tension, contact angles, air films, the surfaces 

 of liquids and solids, flocculation and deflocculation, frothing or foaming. The 

 practice of flotation is described and an account given of the various hypotheses 

 advanced to explain flotation. This is an extensive paper on a difficult but 

 exceedingly important subject. 



Colloids in Catalytic Hydrogenation. By E. F. Armstrong, D.Sc, F.R.S., and 



T. P. Hilditch, D.Sc. 



Colloid phenomena obtain in the hydrogenation of gaseous or liquid organic 

 compounds : (1) because of the surface at which interaction occurs; (2) when 

 catalysts in the colloidal condition are employed. Catalysts may be colloidal 

 sols or finely divided metals, non-supported or supported. The various physical 

 and chemical conditions involved are considered, as well as the various theories 

 of catalysis. 



77(6 Eole of Colloids in Electrolytic Metal-Dejiosition. By Henry J. S. Sand, 

 Ph.D., D.Sc, F.I.C. (Sir John Cass Technical Institute, London). 



The influence of colloids in electrolytic plating solutions on the metal deposits 

 obtained has been discussed under the headings : Phenomena produced by 

 addition-agents; inclusion of the addition-agent in the metal-deposit, and its 

 colloidal nature ; adsorption and gold number of colloids in relation to their 

 effectiveness as addition-agents; microstructure of deposits containing colloids; 

 equilibrium potential of deposits containing colloids (transfer-resistance and 

 polarisation) ; over-voltage produced by colloids in its relation to improved 

 throwing-power of electrolytic baths, and to the sequence of electrolytic pro- 

 cesses taking place at the electrodes ; nature of process by which the final 

 structure of electrolytic metal deposits is brought about; colloids at the anode; 

 colloids in applied metal deposition. 



Buhher. By Henry P. Stevens, M.A., Ph.D., F.I.C. 



In the first report (1917) Dr. Stevens gave a summary of the chief papers 

 on rubber. This bibliography is now extended and brought up to date, and 

 the properties of rubber are discussed from the colloidal view-point. Vulcanisa- 

 tion is treated in detail. 



Colloidal Fuels: their Preparation and Properties. By A. E. Dunstan, D.Sc, 

 F.I.C. (Chief Chemist, Anglo-Persian'Oil Co.). 



This paper is a brief summary of recent work, particularly in the United 

 States, on colloidal fuels. 



