274 REPORTS ON THE STATE OF SCIENCE, ETC. 



Colloid Chemistry and its General and Industrial 

 Applications. — Summary Report of Covimittee (Professor F. G. 

 DoNNAN, Chairman; Dr. W. Clayton, Secretary, Dr. E. Ardern, 

 Dr. E. F. Armstrong, Sir W. M. Bayliss, Professor C. H. Desch, 

 Dr. A. E. DuNSTAN, Mr. H. W. Greenwood, Mr. W. Harrison, 

 Mr. E. Hatschek, Mr. G. King, Professors W. C. Mc.C. Lewis 

 and J. W. McBain, Dr. E. S. Morell, Professors H. E. Proctor 

 and W. Eamsden, Sir E. J. Eussell, Mr. A. B. Searle, Dr. S. A. 

 Shorter, Dr. E. E. Slade, Mr. F. Sproxton, Dr. H. P. Stevens, 

 Mr. H. B. Stocks, Mr. E. Whympee). 



The publication of the Fourth Report was unavoidably delayed for many 

 months, but it was published in August 1922 by H.,M. Stationery Office. The 

 following papers, eight of academic nature and six on industrial subjects, are 

 included in the Report : — 



Colloid Problems iv Analytical Chemistry. By Prof. H. Bassett, D.Sc, Ph.D., 

 D. es So., F.I.C. (University College, Reading). 



The fundamental colloid phenomena underlying most analytical operations 

 are discussed, especially in connection with the formation, purity, filtration, and 

 washing of precipitates. The colloid properties of the filter-paper, surfaces of 

 vessels, &c., are also discussed. The Report includes a selection of important 

 analytical determinations in inorganic and organic chemistry, illustrating the 

 colloid principles under discussion. 



Catajihoresis : The Motion of Colloidal Particles in an Electric Field. By Prof. 

 E. F. Burton, M.A., Ph.D. (University of Toronto, Canada). 



This paper is a summary of the main points in connection with cataphoresis, 

 and includes recent work carried out in Prof. Burton's laboratory on the tech- 

 nique of cataphoresis. 



Colloid Systems in Solid Crystalline Media. By Prof. Cecil H. Desch, D.Sc, 

 Ph.D. (University of Sheflfield). 



The dispersion of solid particles throughout a crystalline solid, when the 

 state of subdivision is sufficiently fine, introduces colloidal characteristics of 

 interest in metallurgv and mineralogy — e.g. the hardening of steel and of certain 

 iron-ferrous alloys, by quenching from a high temperature, and the colouring 

 matters in crystalline minerals. 



Molecular Attraction and the Phy-ncal Properties of Liquids. By Edwin Edser, 

 A.K.C.Sc, F.Ph.S., F.Inst.P. (Minerals Separation, Ltd., London). 



The law of molecular attraction derived in this paper may be stated as 

 follows : Two molecules attract each other with a force that varies inversely as 

 a power of the distance separating them, and this power must be higher than 

 the fifth. In all liquids the result of analysing the experimental data is to 

 indicate that the molecules attract each other inversely as the eighth power of 

 the distance separating them ; mercury, however, is not in good agreement with 

 this law. 



It is deduced from this law that : (1) Of the energy which represents the 

 surface tension of a liquid, 94 per cent, is located in the surface layer one 

 rriolecule diameter in thickness, while the remainder is located at a greater 

 distance from the surface ; (2) at a distance of one molecule diameter from the 

 surface of a liquid the intrinsic pressure is 8.5 per cent, less than the maximum 

 value in the interior of the liquid. 



