ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 275 

 Membrane, Equilibria. By VV. E. Garner, M.Sc. (University College, London). 



The remai-kable potential differences occurring at cell surfaces — i.e. at the 

 surfaces of membranes in contact with electrolytes — are discussed in the liglit 

 of the theories due to Ostwaid, Haber and Klemensiewicz, Loeb and Beutuer, 

 and Donnan. Special consideration is given to Donnun's theory based on thermo- 

 dynaniical treatment. 



Disperse Systems in Gases. By VV. E. Gibbs, D.Sc. (Chief Chemist, The Salt 



Union, Ltd., Liverpool). 



The methods of formation of disperse systems in gases are studied — e.y. 



(1) by the condensation of a gas or vapour in the presence of suitable nuclei; 



(2) by the disintegration and dispersion of a liquid or solid. Those systems 

 in which the particles are too large to exhibit Brownian motion at ordinary 

 temperature and pressure are termed ' clouds,' while the more highly disperse 

 systems are called ' smokes.' 



The properties of these gas-solid and gas-liquid disperse systems are con- 

 sidered in the following order : (1) their mechanical properties — the concentra- 

 tion, the motion of the particles, and the degree of dispersion ; (2) their optical 

 properties— the absorption, reflection, refraction, and diffraction of light by 

 the system; (3) their thermal properties— the absorption and radiation ot heat; 

 (4) tlieir electrical properties — the electrical charges upon the particles, their 

 behaviour in an electric field ; (5) their chemical properties — the increased 

 chemical activity of the disperse system, due to its high degree of dispersion. 



The industrial applications are dealt with, and tlie paper concludes with a 

 section on Chemical Warfare. 



The Theory of Lubrication. By W. B. Hardy, M.A., F.R.S. 



' A theory of lubrication must be founded upon a general theory of friction. 

 No such general theory, however, exists, but in its place there is a theory of 

 internal friction or viscosity which refers the resistance to fundamental forces 

 between molecules, and a theory of external or superficial friction which, standing 

 where Coulomb left it in 1781, accepts accidental inequalities of the surfaces 

 as a sufficient cause.' The theories of Coulomb, Reynolds, and others are dis- 

 cussed, and a theory proposed, based on molecular orientation in surfaces, 

 according to which one would expect ' that in general any good lubricant would 

 be more strongly attracted by the bounding solid faces than a bad one. The 

 expectation can only be a general one, because lubricating qualities depend not 

 only upon the intensity of such attraction, but also upon the kind of orientation 

 of the molecules produced by it, and the variation of potential energy in the 

 lubricant and surf ace of the solid produced by traction.' 



The Aj)plication of Colloid Chemistry to Mineralogy and Petrology. By 

 Alexander Scott, M.A., D.Sc. (Central School of Pottery, Stoke-on-Trent). 



The general principles of colloid chemistry are applied to important pheno- 

 mena in mineralogy and petrology, and special attention is given to those rocks 

 and minerals which exist in a colloidal form, or are derived from colloidal 

 material. Weathering, cementation, adsorption, ore depcsits, concretionary and 

 banded structures, dendritic structures, igneous rocks, &c., are discussed as 

 colloid problems. Rocks and minerals in large number are considered in much 

 detail, and investigations mentioned which are needed to extend our knowledge 

 of the mechanism of well-known natural phenomena. 



Colloid Chemistry of Soap. Part II. The Soap Boiling Processes. By Prof 

 J. W. McBain, M.A., Ph.D., and Ernest Walls, M.A. (The University, and 

 Broad Plain Soap Works, Bristol). 



"The first part of the report deals with the actual works practice of soap- 

 boiling. The second part treats of the theory of soap-boiling, under the head- 

 ings : Historical, general review, hydration of the fibres in soap curd. The 

 third part of the report is entitled 'Application of the Theory,' and deals with 

 saponification, graining and washing, fitting and settling, and the colour and 

 hardness of soaps. 



