CHEMICAL NEWS, Osmotic Pressure. PROCEEDINGS OF SOCIETIES. ROYAL SOCIETY. Ordinary Meeting, May 17, 1917. Sir J. J. THOMSON, O.M., President, in the Chair. THE Bakerian Lecture was delivered by Mr. J. H. JEANS, F.R.S., on "The Configurations of Astronomical Masses and the Figure of the Earth." A study of the forms which can be assumed by masses of actual compressible matter under their own gravitation is of obvious importance for cosmogony and astronomy. A theorem of fundamental importance is that for a given mass, acted on by given forces and rotating at a given speed, there is only one equilibrium arrangement of the internal strata when the boundary is fixed. Thus possible figures of equilibrium can be classified by their boundaries; the interior matter will arrange itself. A simple application is to the Figure of the Earth. Regarding the earth's surface as roughly spherical, the internal layers of equal density must be concentric spheres. The view that the internal strata may be, or in some past age may have been, excentric, is found to be illusory, and an attempted explanation of the major inequalities of the earth's surface in terms of this idea fails. A more complex application is to the figures of compressible masses, such as gases, in rotation. It is found that a shrinking compressible mass will, in general, assume in turn figures which may be described as pseudo spheroids and pseudo-ellipsoids, these being derived by continuous distortion from the spheroids and ellipsoids which form the only stable figures of equilibrium for incompressible masses. more lens-shaped than a The pseudo- spheroids are spheroid, and the pseudo-ellipsoids are more spindleshaped than an ellipsoid. A sharp periphery may develop on the pseudo spheroid or a sharp point on the pseudoellipsiod, in which case streams of matter are ejected through centrifugal force outbalancing gravity. Considering in detail the figures appropriate to the law PROY, it is found that a sharp periphery will develop on the pseudo-spheroids before the series of pseudo-ellipsoids is reached if y<3 (approximately). Thus a mass of ideal gas for which can never attain the pseudo-ellipsoidal form, and so can never divide into two detached masses. But as the density of an actual gas increases with shrinkage, the ideal laws are departed from. The value y = 3 is reached, perhaps, at a density of to, roughly that of a So far, then, a "giant" star can lose matter B-type star. This agrees equatorially, but cannot divide by fission. The latter process can only begin at about type B. exactly with Campbell's discussion of spectroscopic binaries. In an actual star internal ionisation and pressure of radiation must be considered, so that a star of sufficient mass can break up before B-type is reached, and there can be "giant" double stars. The results obtained fit in well with observation, and suggest a simple view of stellar cosmogony. A GENERAL DISCUSSION took place on "Osmotic Pressure." Sir OLIVER LODGE then took the chair. Sir Oliver referred in the first instance to the general importance of the subject in animal and vegetable economy. That was the practical side; but the discussion was to concern itself with the theoretical side. Osmosis depended essentially on molecular discrimination, and this brought it into relation with evaporation and freezing. The subject could be treated either thermodynamicallydisregarding what actually goes on-or from the kinetic standpoint, and that was how the authors of the papers dissolved substance, Mr. Bousfield to the solvent, and Dr. would treat it: Dr. Porter applying the gas theory to the Tinker dealing with the matter on a cohesion basis. Prof. ALFRED W. PORTER, F. R.S., then opened the disThe investigations of Perrin and others upon Brownian Cussion by the presentation of his paper. motion have demonstrated once for all that the molecular translatory agitation in a liquid is precisely that which is never proved. In considering a solute the dynamical effects given by gas theory. This had long been suspected but of this motion must be taken into account; when the solution is dilute it comes out equal to the experimental must not only explain it, but at the same time must explain value of osmotic pressure. Any other theory of osmosis away the effects of molecular agitation. Of course, when or the properties of the membrane which make it semithe processes by which the final equilibrium state is set up, permeable, come to be examined, many interesting conto express osmotic pressure in terms of them; but the nections will certainly be found which will make it possible causa causans of the whole phenomenon is the molecular bombardment of the solute, and a knowledge of this propressure has been calculated from any direct theory of the vides us with the only way in which the value of the mechanics of the solution. The properties of the membrane form a subsidiary problem; they have as much to do with osmotics as the properties of a glass vessel have upon the origin of the pressure experienced from water contained in it. = The experimental values of Lord Berkeley and Morse mately represented by a formula of Hirn's type, P (v-b) and their co-workers for sugar solutions can be approxiRT; but the values of bare larger than the volume occupied by the sugar itself. The excess can be attributed this way from Morse's determinations diminishes with to water of hydration. The hydration number found in tration. The extreme values are 53 and about 3. The increase in temperature, and also with increase in concenvalue 53 occurs only in a very dilute solution, and the correIf the sponding value obtained from Berkeley's experiments is molecules of sugar and water are represented by spheres only 14, which seems a more likely number. of volumes equal to their molecular volumes, between 30 and 45 molecules of water would form a single layer on each sugar molecule. It is exceedingly likely a priori that There is densed layer on it which will be continually breaking up the water round a sugar molecule tends to form a conunder the influence of molecular collisions. water molecules with each other; mono-, di-, tri-hydrol nothing in osmosis to indicate the degree of association of are indistinguishable. Doubt is thrown upon the meaning of the symbol N in Poynting's and Callendar's modifications of Raoult's equation. Their theories require that N shall be the total number of real molecules of solvent, whereas thermodynamical theory and experiment require that it shall be the number reckoned as of the same complexity as in the vapour state. Osmotic pressures can be obtained indirectly from vapour pressures by an exact relation first given by the opener; this has been done experimentally by Lord Berkeley. They can also be obtained from latent heats or by a better-known approximate formula :of dilution either by an exact formula given by the opener H; = uT? JT (F). Ꭲ Values of Hi are being determined by D. O. Wood; some of these are published now for the first time, and Morse's determinations are checked by them. This mode of in direct determination of osmotic data is very exact because H depends only upon deviations of P from the perfect gas law, being zero when P is proportional to T. Dr. F. TINKER then presented his paper on "The Colloidal Membrane: Its Properties and its Function in the Osmotic System." In this contribution the kinetic side of the subject of osmosis is developed by the aid of data obtained from the experimental study of colloidal membranes. Evidence is brought forward to show that moisture flowing through a semipermeable membrane is absorbed or superficially condensed on to the surfaces of the colloidal particles composing the film for such time as it is in contact with the membrane. Generally speaking, osmotic flow takes place from a pure solvent to a solution because the pure solvent induces a greater pressure of concentration of moisture inside the membrane than the solution does. The condition for osmotic equilibrium is uniformity of moisture pressure and concentration within the membrane. To establish this uniformity, a hydrostatic pressure has usually to be placed on the solution in order to bring the moisture pressure generated by it inside the membrane up to that generated by the pure solvent. The particular hydrostatic pressure which does this is defined as the osmotic pressure of solution. The evidence adduced points to the conclusion that osmotic diffusion is a process similar in character to, but not identical with, the process of vapour distillation. The main difference between the two processes is that the moisture within a membrane is in a much more concentrated condition than it is inside the vapour phase proper. But the resemblance is so great that for purposes of argument and mathematical treatment we can replace the actual membrane by a vacuum; at least this is the case when considering quantities, such as the magnitude of the osmotic pressure, whose value is independent of the nature of the membrane. By means of this simple device the process of vapour distillation becomes a particular type of osmotic diffusion, viz., osmotic diffusion across a vacuum. We can consequently arrive at many of the factors governing the magnitude and direction of osmotic flow. and the magnitude of the osmotic pressure, by considering the factors which determine the relative values of the vapour pressures of the pure solvent and solution respectively. This is done in the latter part of the paper. Mr. W. R. BOUSFIELD, K.C., F.R.S., then gave his paper entitled "Osmotic Pressure in Relation to the Constitution of Water and the Hydrates of the Solutes." This paper deals with the subject of osmotic pressure from the standpoint of the ternary constitution of water, which alone can explain the curious fact that for a very dilute solution of sugar the osmotic pressure at o° C. is greater than that at 5°. The vapour pressure theory is shown to be sufficient to explain all the phenomena with. out postulating osmotic pressure as an "expansive force." It is shown that the osmotic relationships can be deduced with great accuracy on the simple hypothesis that the steam molecules in water behave as a perfect gas in the interstices of the solution. The conclusion is that it is not the solute but the interstitial vapour of the solvent which behaves as a gas, and that it is not the activity of the solute but that of the solvent vapour which is responsible for the phenomena. Mr. W. R. BoUSFIELD proceeded to discuss the views put forward by Prof. Porter. A theory which left out of account, comparatively speaking, the activity of the solvent, seemed to him the wrong way of looking at things. Criticising the contention that the diffusion, say, of sugar introduced into a solution indicates an expansive force, he maintained that osmosis might be equally regarded as due to the water expanding in the opposite direction. If the pressure of sugar arose from its thermal motion, why at the surface was it the vapour of the water which escaped and not the sugar? What really obeyed the gas law in solution was not the solute but the occluded vapour comprised in the solution. Figures calculated from his theory agreed with those observed more closely than those deduced from Prof. Porter's theory. Dr. S. A. SHORTER held that the "gas law" of osmotic pressure, though simple from an algebraical point of view, was very complex from the point of view of the kinetic theory, so that the law formed a very unsatisfactory basis for the theory of the ideal dilute solution. The correct the partial pressure of the solute was proportional to its basis for the theory was Henry's law, which stated that concentration, and which was readily established on theoretical grounds-simply following from the obvious consideration that the field of force, in which each solute molecule moved, was not affected by the addition of further solute molecules. The constant of proportionality depended upon the nature of the intermolecular forces, being vastly greater in the case of, say, solutions of benzine in water, than in the case of, say, solutions of methyl alcohol in water. From Henry's law we could readily establish Raoult's law and the "gas law" of simple theoretical considerations, and neither of which osmotic pressure, neither of which could be deduced from contained any reference to intermolecular forces. This latter point constituted a grave defect in the ordinary osmotic theory. Since it ignored intermolecular forces in in concentrated solutions, and to adopt the totally undilute solutions, it led many investigators to ignore them justifiable procedure of postulating certain ideal properties of a concentrated solution, and then ascribing departures from this ideal to chemical action (dissociation, associasideration of the theoretical basis of Henry's law, that tion, or solvation). Now, it was evident, from a conwith concentration of the partial pressure of the solute in intermolecular forces must control the mode of variation a concentrated solution. The same must be true of the partial pressure of the solvent, and of the osmotic pressure, since they were both related thermo dynamically to the partial pressure of the solute. Theories of the chemical structure of concentrated solutions, based on the concept of the ideal concentrated solution, were fundamentally unsound. the processes operative in solutions was the further deThe most necessary step towards a fuller knowledge of velopment of the kinetic theory of solution. The points to be explained first of all were not the comparatively minute deviations from some imaginary ideal behaviour exhibited by certain solutions, but such broad questions as the existence of different types of partial vapour pressure curves, the total or partial miscibility of liquids, the existence of a critical temperature with respect to miscibility, &c. The EARL OF BERKELEY, F.R.S., as an illustration of one of the difficulties in the internal vapour pressure theory, referred to the diffusion which would take place if a layer of potassium bichromate were placed at the bottom of a column of concentrated sulphuric acid, the vapour pressure of which was practically nil. He inquired as to the accuracy of the latent-heat method of measuring osmotic pressure. Prof. J. C. PHILIP stated difficulties he felt with regard to Dr. Tinker's explanation of the selective action of the membrane. As far as size was concerned, a sugar molecule could pass through the pores of the membrane. If the pores had the power of absorbing water, why should not that water absorbed itself take up the sugar molecules making the membrane "leak"? Recent experimental work on hydration led to somewhat higher figures for the average number of water molecules associated with sugar in solution than the numbers assumed by Mr. Bousfield, namely, from 11 in dilute down to about 7 in strong solutions. Prof. Porter had obtained similarly higher figures. Dr. G. SENTER, while agreeing largely with Prof, Industrial and Manufacturing Chemistry. CHEMICAL NEWS, June 1, 1917 Porter's theory, criticised his views on hydration, and in particular the assumption that the uncertainty in the value of bin Hirn's equation was to be accounted for by hydration. Mr. W. C. DAMPIER WHETHAM, F.R.S., was of opinion that the relations between osmotic phenomena and vapour pressure and freezing-point which Mr. Bousfield had deduced amounted in effect merely to a confirmation of thermodynamic relations. To get a satisfactory theory of the mechanism of osmotic pressure it was necessary to begin with first principles, and he thought the gas theory the only one which enabled this to be done. Prof. A. FINDLAY, in a written communication, emphasised the importance of distinguishing between the equilibrium pressure and the process by which this was produced. The process of osmosis and the role of the membrane had little reference to the main problem of the value of the equilibrium pressure and its relation to the constitution of the solution. He combated the view that osmotic pressure (a term he thought misleading) was to be identified with the expansive force that brought about diffusion, and he could not accept Prof. Porter's kinetic treatment of the problem. The weakness in this arose from the use of the equation P(v—b) RT in attributing deviations from it to hydration, The connection between heat of dilution and osmotic pressure seemed a fruitful direction for investigation. He favoured the view, mooted by Tammann, that osmotic pressure was caused by the inner compression of the solvent in solution. Some recent calculations by Horiba lent support to this theory. = Mr. J. R. PARTINGTON, in a written communication, showed how it followed from molecular theory that although the physical state of the dissolved molecules might not be comparable with that of the gaseous molecules, yet they could behave with respect to bombardment as if they were in the state of a gas. The question as to whether the osmotic pressure was "caused" by solute or solvent appeared to him to be largely meaningless. Mr. F. S. SPIERS (communicated) considered that a satisfactory conception of osmotic pressure was arrived if one regarded it as the diminution in the kinetic molecular energy of the solvent due to association with the solute. This view not only took account of both solvent and solute, but it also gave a simple picture of the process of osmosis, and suggested at once the connection between osmotic pressure and vapour pressure. Prof. ALFRED W. PORTER replied at this stage to some of the criticisms that had been made. The solute molecules contribute nothing to vapour pressure, simply be. cause when they get near the surface they are drawn downward by the solvent and never succeed in escaping. The answer to Dr. Philip was, he thought, that the canals in the membrane must be narrow compared with the range of molecular action, although not necessarily compared with molecular dimensions. In answer to Lord Berkeley, the method of using latent heat of dilution to determine osmotic pressures gave very considerable accuracy. He reserved his full reply for the printed report of the discussion. Prof. T. S. MOORE considered that the modification of the gas theory required to explain the action of a solute in solution was so fundamental that it ceased to be a gas theory. The internal pressure of a solution being exceedingly high, it was impossible to suppose that the pressure exercised by the solute molecules could be independent of the solvent molecules and of the forces exerted by the solute on the solvent, which were the assumptions made by Prof. Porter. A molecular theory of osmotic pressure must form part of a general molecular theory of solution. Sir OLIVER LODGE, in bringing the discussion to a close, pointed out that in a liquid they had to deal with an internal pressure, due to the mutual attraction of the molecules, of great magnitude. The source of osmotic pressure was probably to be looked for in this internal pressure. NOTICES OF BOOKS. 263 Industrial and Manufacturing Chemistry. Part II. Inorganic. By GEOFFREY MARTIN, Ph.D., D.Sc., F.C.S. Volume I. London: Crosby Lockwood and Son. 1917. Pp. xix+496. Price 25s. net. THIS book is the companion volume to the author's "Treatise on Industrial Organic Chemistry," and is very similar to it in scope and plan. The impossibility of treating adequately the whole of industrial inorganic chemistry, even in two large volumes, is obvious, and although the editor has, on the whole, apportioned out his space wisely and has benefitted by the co-operation of a representative set of able collaborators, the descriptions of the technical processes are in some cases necessarily rather meagre. An enormously wide field is covered in the 51 sections which comprise the book, including fuels, gases, acids, salts, the liquefaction of gases, pyrometry, the technology of water, &c., and much attention has been paid to patent literature, and to modern processes and plant, details of which are in some cases published for the first time in book form. Diagrams and illustrations are very numerous, and the references to literature are full and detailed. The value of the book would probably be greater to technical students and to practical business men who want a survey of a good many branches of industrial chemistry than to the specialist in any one branch. Chemistry for Beginners. By C. T. KINGZETT, F.I.C., F.C.S. London: Baillière, Tindall, and Cox. 1917. Pp. vi+106. Price 2s. 6d. net. THE advisability of giving some simple scientific instruction to all children is in process of being recognised by educa. tional authorities and parents, and it is most desirable that any distinction in this respect between the children of the rich and the poor should be reduced to a minimum. Any book therefore which is intended, as this, for use in primary and public schools should be assured of attention and welcome, if it appears satisfactory for its purpose. Physics and chemistry ought certainly to take very important places among the sciences, if they are not given precedence of all others in the school curriculum. The obvious criticism to be made with reference to this book is that its price is heavy for its scope and size. In addition, although it contains a very fair amount of information, it appears rather doubtful whether the material is put before the pupil in such a way as to make him use his reasoning power. The first part deals with the constitution of matter and the elements of the atomic theory, and would probably be found a rather difficult beginning for the average boy or girl. Part II. on "Force and Energy" is, on the whole, more likely to prove interesting, but the third part, in which short descriptions are given of the chief elements and compounds, is packed much too full of facts which will stand very little chance of being properly assimilated. Nevertheless, for the general reader who is review of the chief facts and will possibly help in the interested in chemistry, the book will provide a useful spreading of scientific knowledge in this country. Guide to the Registration of Business Names Act, 1916. By KENNETH BROWN. London: Sir Isaac Pitman and Sons, Ltd. Pp. vii+51. Price is. net. THIS little book gives in clear and unequivocal language precise information as to the provisions of the Registration of Business Names Act. Details of the circumstances in which registration is obligatory, the particulars which have to be furnished on registration, and the penalties attached to failure to comply with the Act are stated so plainly that it would appear to be impossible for anybody to misunderstand them. Many difficult and obscure points are fully discussed, and the full text of the Act is included, and business men will find that the book gives clear and concise guidance on questions relating to the registration of busi ness names. The Journal of the Institute of Metals. Volume XVI. Edited by G. SHAW SCOTT, M.Sc. London: The Institute of Metals. 1916. Pp. ix +370. THIS Volume of the Journal of the Institute of Metals contains the 1916 May Lecture, delivered by Prof. W. H. Bragg on "X-Rays and Crystal Structure, with Special Reference to Certain Metals." The work of Prof. Bragg and others on the structure of crystalline materials may truly be described as laying the foundations of a new science, and undoubtedly results of the most far-reaching importance are awaiting investigators who employ the new methods of research which Prof. Bragg and his son have elaborated. Although it was not possible in the lecture to give more than a sketch of the work on X-rays and crystalline structure this was done in a very interesting and illuminating manner. Three papers on the annealing of arsenical brass, the allotropy of silver, and the development of the spelter industry, with accounts of the discus sions which followed them, form the bulk of the book, which also contains short abstracts of papers on metals and metallurgy published in various English and other journals during 1916. Dominion of Canada, Department of Agriculture. Report of the Division of Chemistry. By FRANK T. SHUTT, M.A., D.Sc. Ottawa: J. de L. Taché. 1916. In this report of the work of the year 1915-1916 the Dominion chemist, Dr. F. T. Shutt, announces that some of the research work of the Division of Chemistry has had to be abandoned owing to the absence on active service of some of the members of the staff, and the impossibility of getting sufficient skilled assistance to continue all the work contemplated or begun. 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