Abstract
LONDON. Royal Society, January 25.—Sir Charles Sherrington, president, in the chair.—A. V. Hill: The potential difference occurring in a Donnan equilibrium and the theory of colloidal behaviour. Loeb has shown experimentally that there is a potential difference between a colloidal solution of a protein and a crystalloid solution with which it is in equilibrium across a membrane, impermeable to the protein, but permeable to the other bodies involved. It varies in the same general manner as the osmotic pressure, the viscosity and the swelling. The variation can be deduced, in general, from the theory of the Donnan equilibrium. One of the chief arguments employed by Loeb, however, is incorrect. Loeb shows that the potential difference observed experimentally agrees very exactly with that “calculated” from the difference in hydrogen ion concentration, also observed experimentally. This is a necessary consequence of the manner in which the observations were made.—E. F. Armstrong and T. P. Hilditch: A study of catalytic actions at solid surfaces. X.: The interaction of carbon monoxide and hydrogen as conditioned by nickel at relatively low temperatures. A practical synthesis of methane. A mixture of equal volumes of carbon monoxide and hydrogen passed over nickel at temperatures 220–280° C. was largely transformed into methane and carbon dioxide: 2CO + 2H2 + CH4. This action affords the simplest and most economical means of producing methane in quantity, since a suitable gas mixture exists in ordinary commercial water-gas when the latter has been freed from catalyst poisons by removal of sulphur compounds. The experimental data obtained are compatible with a combination of the “water-gas reaction” with the normal hydrogenation process. Thus, of two volumes of water-gas (2CO + 2H2), one molecule of carbon monoxide and a molecule of water interact and yield a molecule each of carbon dioxide and of hydrogen, the latter, with the balance of hydrogen present in the original gas, furnishing sufficient hydrogen for the normal hydrogenation of a second molecule of carbon monoxide.—J. Holker: The periodic opacity of certain colloids in progressively increasing concentrations of electrolytes. The method of testing the effect of common salt on the typical emulsoid colloid, serum, was described. Into each test-tube was pipetted 0.5 c.c. of undiluted serum and to each was then added 2 c.c. of solution of sodium chloride, which progressively increased in concentration in each successive tube. The tubes were shaken and placed in a thermostat at 40° C. for four hours. Then the opacity of the solution was determined. The phenomenon is periodic and is given by colloids of both the emulsoid and suspensoid type, and by animal, vegetable, and mineral colloids. It is also given by certainmixtures of simple aqueous solutions of inorganic salts. Emulsoid colloids tend to give many oscillations of low amplitude. Suspensoid colloids tend to give few oscillations of high amplitude. The phenomenon is not an optical interference of the light scattered by colloidal particles, but is a definite oscillatory change in the physical condition of those particles.—E. K. Rideal and R. G. W. Norrish: The photochemistry of potassium permanganate. Pt. I: The application of the potentiometer to the study of photochemical change. Pt. II.: On the energetics of the photo-decomposition of potassium permanganate. The electrode potential of potassium permanganate when illuminated with ultra-violet light from the mercury vapour lamp undergoes a change (ca 0.25 volt) and recovers slowly in the dark. This change is correlated with a photochemical decomposition of the permanganate, made apparent by the separation of a precipitate of the composition K2O. 2MnO2, and the formation of a sol of MnO2. Illumination establishes a photochemical stationary state, KOH being simultaneously produced by the decomposition, and removed by combination with the colloidal MnO2. This involves an alteration of the PH of the solution, which causes the electrode potential changes. The decomposition is monomolecular over the range of concentrations investigated. The decomposition of acidified permanganate under identical conditions is of zero order, due to non-formation of colloid. The photoactive radiation lies in the ultra-violet absorption spectrum of potassium permanganate, and the Hg line at 3128 ÅU is considered the chief agent. The quantitative absorption of radiant energy is in agreement with the Einstein Law of Photochemical Equivalent, a result of special interest as the first instance of its application to solutions.—E. A. Fisher: Some moisture relations of colloids. Pt. I.: A comparative study of the rates of evaporation of water from wool, sand and clay. Curves obtained by plotting rates of evaporation against water contents are discontinuous. Each portion of the rate curve can be expressed by a simple type of equation connecting rate of evaporation with water content. The rate curves obtained are similar in type in the cases of wool (wholly colloidal with a cellular structure), quartz sand (wholly non-colloidal with a granular structure), silty soil (notoriously feeble in colloid properties), and heavy clay sub-soil (typically colloidal in behaviour). The so-called shrinkage of wool on drying is really a deformation and not a volume shrinkage. The absorption of water by wool is attributed primarily to a filling up of fine pores of various shapes and sizes; the vapour pressures of wool-water systems are determined by the diameters of the pores that are full of water.—R. Whytlaw-Gray, tB. Speakman and J. H. P. Campbell: Smokes Pt. I.: A study of their behaviour and a method of determining the number of particles they contain. The smokes wexe produced (a) by the arc discharge in air, (b) by volatilisation and condensation, (c) by chemical action. In each case highly dispersed systems of very minute particles were obtained. Examined in an ultra-microscope of the slit type, the life-history of a smoke falls into two main periods:—(a) An unstable period in which the number of particles diminishes rapidly with time, (b) A stable period in which the decrease in number is slow. During the first period the increase in size is very marked; the changes are not due to evaporation but to a process of aggregation, which produces complexes of different structure depending on the nature of the dispersed substance.—R. Whytlaw-Gray and J. B. Speakman: Smokes. Pt. II.: A method of determining the size of the particles they contain. A filtration method is used which enables the concentration in weight of the suspended solid matter in rapidly changing smokes to be determined with an accuracy of about 3 per cent. A given volume of smoke (usually 1 litre) is filtered through small tubes containing asbestos, and the increase in weight is ascertained by a micro-balance sensitive to 0.0002 mgm. Filtration takes about five minutes. Curves have been obtained showing the variation in weight concentration of the smoke over periods of 0–6 hours. Knowing the weight and the number of the particles in a given volume, the average mass of a smoke particle at different periods can be calculated and the growth followed quantitatively. Assuming the density of the particle to be that of the substance in bulk the average radius can be evaluated. All the weight-concentration curves show an initial rise, and this fact, in conjunction with ultra-microscopic observations, renders it probable that all these clouds contain in the early stages a large number of invisible particles of a microscopic size.—R. C. Ray: The effect of long grinding on quartz (silver sand). When quartz (silver sand) is ground for a long time the density of the ground substance is lower than the one which has not been subjected to grinding. The fall of density shows that as much as 25.7 per cent. of the material is converted from the crystalline to the vitreous condition. This value agrees fairly with that derived from the molecular heats of solution.
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Societies and Academies. Nature 111, 168–172 (1923). https://doi.org/10.1038/111168a0
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DOI: https://doi.org/10.1038/111168a0