water.

The crucible is then cleaned with hydrochloric acid (1 : 1), and the contents are poured into the beaker or dish. By gentle heat and cautions pressure with the flattened tip of a rod the lump or lumps are caused to disintegrate and pass largely into solution in a few minutes. A certain amount of silica may remain undissolved in a flocculent state, but this of no moment. When all grit has disappeared, the liquid, if in a beaker, is washed into a dish and evaporated to dryness. If solution was made directly in the dish the volume of liquid need not exceed a few cubic centimetres and the evaporation takes but a short time. A much smaller dish is allowable than in the case of wholly siliceous minerals, because of the small bulk of solution and the entire absence of added fixed salts.

. By solution in acid after heating with sodium carbonate.-When the siliceous components are in such amount as not to permit the formation of a wholly soluble product by strong ignition, it is necessary to mix sodium carbonate with the powder and decompose the silicates by its aid over the blast lamp. This procedure may be adopted with all siliceous limestones if desired. The amount of flux to be used is but a fraction of that needed for a silicate analysis. One-fourth to one-half grm. for 1 grm. of limestone suffices (P. W. Shimer, in R. K. Meade, "The Chemist's Pocket Manual," p. 162), for the lime formed by ignition is itself a powerful flux, and it is quite unnecessary to have here a liquid fusion. A sintering suffices. This proportion holds also for highly magnesian limestones and for cement rocks containing as little as 50 per cent of lime (personal communication from R. K. Meade).

B. SEPARATION OF SILICA,

Because of the absence of large amounts of alkali salt and of much silica and the evaporation of the hydrochloric acid solution obtained in A, a, and b, a, and 8, takes little time as compared with a silicate analysis. When dry, or nearly so, on the steam bath, the dish may be placed in an air bath or (covered) on a platinum triangle resting on a hot plate, and heated to 200° for an hour if a limestone is under treatment, but for a highly magnesian limestone the temperature should not exceed 120°, according to J. P. Gilbert (Tech. Quart., 1890, iii., 61; Abstract in Zeitschr. anal. Chemie., 1890, xxix., 688) because of recombination of silica and magnesia, with subsequent resolution of the silica when acid is added.

Bertram Blount claims (Jour. Soc. Chem. Ind., 1902, xxi., 1217) that by heating to 200° in this manner the silica is completely separated by a single treatment, but I have not found it so, though the amounts going into solution on subsequent addition of acid are small, seldom over 2 or 3 milligrms. Therefore, for exact work with silica present to the amount of 2 to 4 per cent and over, that already rendered insoluble should be filtered off and the solution again evaporated. With this end in view the dry mass is drenched with strong hydrochloric acid and allowed to stand for a few minutes, then as much water is added and the dish covered and placed on the bath for 10 minutes. Instead of strong acid that of half strength may be used and the heating begun at once. The silica is then separated by filtration on a filter of suitable size, washed

thoroughly with dilute acid and then twice with cold water. The filtrate is evaporated again to dryness, the residue extracted with hydrochloric acid as before, but with allowance of only a few minutes' time and the solution filtered once more through a second and smaller paper. The two papers with their contents are slowly dried, charred, and ignited in platinum, finally over the blast for 10 minutes. The weighed silica is to be corrected for foreign matter by evaporating with 5 cm. (Jour. Soc. Chem. Ind., 1902, xxi., 1217) of hydrofluoric acid and one or two drops of sulphuric acid. The residue obtained after ignition is almost always considerably less than that found in analysing a silicate rock, and an ignition of a minute or two over a full burner, after expulsion of the sulphuric acid, is in almost all cases sufficient. The composition of this residue is similar qualitatively to that derived from silicate rocks. It should never contain calcium or magnesium but consists mainly of alumina, with a little ferric, titanic, and phosphoric oxides. It is preserved, and the subsequently obtained precipitate of these oxides is added to it and ignited in the same crucible.-Bulletin 700, N. S. Geological Survey.

PROCEEDINGS OF SOCIETIES.

ROYAL SOCIETY.

Ordinary Meeting, November 18, 1920.

Sir J. J. THOMSON, O. M., President, in the Chair.

THE following papers were read :

"The Absorption and Scattering of Light." By SIR ARTHUR SCHUSTER, F.R.S.

The paper is based on the generally accepted theory that refraction and dispesion are caused by the oscillations of electric resonators embedded in the medium through which the light passes. With homogeneous light each resonator responds with a forced oscillation, together with a motion following the laws of free oscillations, and gradually dying out. If the white light falls on the medium, the forced oscillation has to be replaced by an integral and other terms added that are due to disturbances caused by neighbouring molecules.

The principal result of the paper is that all the terms of the equation are spectroscopically identical. If the proper value for f (n,w) be introduced, and E regarded as constant, then the integral in the first term of the right-hand side is merely the analytical representation by Fourier's integral of any of the terms of the summation, with a proper adjustment of and ts. As it stands it represents a motion beginning at time t=0 and continuing according to the laws of a damped oscillator.

The mechanism of scattering and absorption is discused, and Lord Rayleigh's equation for the coefficient of extinction in a scattering medium is obtained in a more vigorous manner, so as to include cases where μ-I is not necessarily small.

The electron currents to a surrounding metal electrode from spherical drops of the liquid alloy of sodium and potassium under the influence of chemical action with a number of gases have been investigated and measured under various condittions. The gas which has been studied most is phosgene (COCI,) then, in decreasing order, Cl2, H2O, and HCI.

In all cases the relation between the current and the applied potential difference is of the same general character. When proper allowance is made for the contact potential difference between the two metal surfaces it is found that the electron currents are nearly constant for small accelerating electric fields. Thus, as in the case of photoelectric emission, the saturation value of the current is reached with a potential difference very close to zero. With retarding fields the currents fall off rapidly as the applied potential difference increases. Like similar thermionic electron currents they approach the voltage axis gradually and not sharply as in the photoelectric case.

The true zero on the voltage scale is difficult to determine on account of fluctuations in the contact potential difference. In the case of COC1, it has been possible to locate the zero to within 010 volt by a photoelectric method.

The proportion of the chemically emitted electrons whose kinetic energy lies between u and u+au is very closely represented by

udu k2 Taе-u/kT

where k is Boltzmann's constant and T is a certain temperature. For the case of COCI, T is near 3300 K, and for the case of Cl, T is about 4900° K. The formula above represents a Maxwell distribution for the temperature T. Thus the distribution of kinetic energy among the chemically emitted electrons is the same as that among the molecules of a gas at the uniform temperature T.

"Magnetism and Atomic Structure.-I." By A. E. OXLEY, M.A., D.Sc.

This communication is an extension of former papers on "The Influence of Molecular Constitution and Temperature on Magnetic Susceptibility" (Phil. Trans. Roy. Soc., 1914, ccxiv. A; 1915, ccxv. A; 1920, ccxx A). From Tyndall's work and

recent experiments of the author on the characteristic deportment of diamagnetic and paramagnetic crystals in the magnetic field, it appears that in non-ionised crystal structures the fundamental unit of the space lattice is the mole

cule.

It is shown that the electron orbits in atoms must be distributed in space round the nucleus, each electron describing a small orbit, or alternatively the electron itself may be a complex unit endowed with magnetic properties. In either case the distribution must be such that he aggregate projected area of the electron orbits on a plane perpendicular to the principal cleavage is a maximum both in diamagnetic and paramagnetic crystals. This result is consistentwith a closer packing of the molecules in a direction parallel to the principal cleavage. In crystals of the simple

structure IS an ionised-atomic one, and the cleavages are all of equal value. Such crystals show no appreciable structural deportment in the magnetic field.

The above views relating to electron distribution are consistent with the cubical atom theory of Lewis and Langmuir, but not with Bohr's theory. The coupling forces between atoms and molecules in non-ionised crystals are due to the mutual magnetic induction between pairs of electron orbits. A model of the hydrogen molecule is given in which the arrangement of the coupling units determines a diamagnetic molecule as required by experiment.

It is considered that the above views and those of Bohr may eventually be brought into line by a fuller recognition of the possible differences between radiating and non-radiating matter.

"The Proximity of Atoms in Gaseous Molecules." By Prof. A. O. RANKINE.

In this investigation a close examination is made of the relations between the estimates of atomic diameters obtained by W. L. Bragg from X-ray crystal measurements and those deduced from the kinetic theory of gases. The examination is carried out from the point of view of the Lewis-Langmuir molecular theory. It is shown that if, for example, a hypothetical molecule be constructed of two argon atoms with their centres separated by the distance demanded by W. L. Bragg's figures, the behaviour of such molecules in thermal agitation would be almost identical with the actual behaviour of chlorine molecules. Similar relations are shown to exist for the pairs of gases, neon-oxygen, krypton-bromine, and xenon-iodine. The following conclusions are regarded as justified :

(a) There is substantial quantitative agreement between the estimates of atomic dimensions deduced from X-ray crystal measurements and from the kinetic theory of gases.

(b) In size and shape the atoms of the monatomic inert elements are nearly indistinguishable from the atoms, respectively, of the neighbouring diatomic elements in the periodic table.

(c) The Lewis-Langmuir molecular theory accounts satisfactorily for the kinetic behaviour of iodine in relation to the behaviour of the corresthe molecules of oxygen, chlorine, bromine, and ponding inert atoms, neon, argon, krypton, and

xenon.

"The Similarity between Carbon Dioxide and Nitrous Oxide." By Prof. A. O. RANKINE.

The two gases in question have been shown by Langmuir to have almost identical physical properties. In particular, they have the same viscosity, and the application of modern kinetic theory indicates that their molecules have the same size and shape. In the present paper, it is shown, by the extension of methods already described by the author, that the kinetic behaviour of the molecules, both of CO, and N,O, is consistent with their being identical in size and shape with three neon atoms in line and contiguous, i.e., with outer electron shells touching. This is in accordance with Langmuir's view of the constitution of these molecules.

"A Graphic Method for the Comparison of Minerals with four variable components forming two isomorphous pairs." By Dr. E. S. SIMPSON.

In the spinel-chromite series the two pairs are MgO,FeO, and Al,O,,Cr,O,, and the general formula is (Mg,Fe)O. (Al,Cr),O,. The relative molecular preponderances of the components of each pair stated as a percentage of the maximum is given by the formulæ x=100(m—f)/(m+f) and y-100(a—c)/(a+c), where m, f, a, represent the number of molecules of MgO,FeO,Al,O,,Cr,O, respectively. The values of x and y, calculated from a number of published analyses, and from new analyses of ceylonite from Camban, Western Australia, are plotted on rectangular coordinates. The four corners of the main square are occupied by the pure compounds MgO.Al2O, (spinel), FeO.Al,O, (hercynite), FeO.Cr2O, (chromite), and MgO.Cr2O, (here named picrochromite). Sub-species and varieties of intermediate composition are divided off in symmetrical areas within the square.

"Fibrolite (=Sillimanite) as a Gem-stone, from Burma and Ceylon." By L. J. SPENCER. Water-worn, prismatic crystals from the ruby mines in Upper Burma measure up to 1 cm. in length, and are clear and transparent, with a pale sapphire-blue colour and marked pleochroism. A fine, faceted gem cut from this material is shown in the British Museum collection of minerals. Determinations were given of the optical constants; the birefringence shows a wide range, y-a being seventeen times -a. On a somewhat similar, but etched, crystal from Ceylon the axial rations were determined. Other crystals from Ceylon are pale greyish-green with a marked chatoyancy.

"The Origin of the Alkali Rocks." By Dr. J. W. EVANS.

The alkali-igneous rocks form an exceptional series varying in composition from acid to basic characterised by a high percentage of alkalies, especially soda, and a deficiency in alumina and the oxides of the divalent elements. They appear to occur mainly in areas where the earth's crust has, as the result of ancient folding or the accumulation of granitic rocks, consolidated to a considerable depth, and where the temperature gradient is normally low. Such areas are rarely subject to new folding, but are frequently folded, and with these faults the alkali rocks appear to have a genetic relation. In such areas crystllisation must proceed in the sub-crystal magmas, which are believed to be basic in composition under exceptional pressure, with the result that minerals with low specific volumes, having regard to the materials of which they are composed, will preferentially crystallise out. Garnet, zoisite, fibrolite, and kyanite are examples, the materials of which crystallise out under less pressure with greater specific volumes. As these minerals are mainly silicates of aluminium and the divalent elements, the uncrystallised residue will be poor in these constituents and rich in the alkalies, especially soda, which was present in the original magma in greater proportion than the potash. It will also contain the volatile fluxes in large amount. As a result of the faulting of the crust, this residue may be pressed out, find its way upwards, and give rise by further differentiation to the alkali rocks.

"Monticellite, from a Mixer Slag." By A. F. HALLIMOND.

The crystals, which are essentially monticellite containing about 20 per cent of olivine in solid solution, have the following physical characters: orthorhombic, ab: c=0'4382: 1: 0'5779; forms 010,110,021; refractive indices 1663, 1674, 1.680; 2V 734°; specific gravity 3 20.

“A_Refractometer for the Determination of Liquid Mixtures.” By Dr. H. H. THOMAS and A. F. HALLIMOND.

A telescope and collimator with Websky signal are fixed in alignment; between then is inserted a parallel-sided trough containing the liquid to be determined, in which is immersed a right-angled prism of known index near that of the liquid. Two images of the signal are formed, and the angular distance between them is read on the eyepiece scale; this reading is proportional to the difference of index between the liquid and the prism. The scale division has the same value whatever the index of the prism used.

SIR,-On page 130 of this Report reference is made to the testing and experimental work carried out in connection with the manufacture of balloon fabrics for war purposes, and in connection with same we wish to place on record this Company's work in the manufacture of materials, especially hydrogen-proof fabric for lighter-than-air craft.

The North British Rubber Company first took up the manufacture of this material in 1908, and realising that the problems involved in manufacture necessitated scientific control, as a preliminary, installed in their laboratory an apparatus for measuring the permeability of rubber to hydrogen, and thereafter initiated research into the factors responsible for the deterioration of rubber under the influence of light.

When the Admiralty installed their Test Station at Manchester, we were requested by the officer in charge to furnish drawings of the special type of hydrogen diffusion apparatus which had been designed at Castle Mills, and one of their staff received a course of instruction in the Company's laboratories on the procedure to be followed in testing balloon fabric. At a later period of the war, this Department was taken over by the newlyformed War Office Aircraft Fabrics Department; who installed an extended testing plant, and another member of that staff also received his training in this work in Aeronautical Laboratories.

Our

The Aeronautical Inspection Department were also indebted to the Laboratory of the North British Rubber Company, Ltd. for the training of some of their scientific staff, and their testing equipment was in many respects also based on the results of this experience.

During the course of the war our output was steadily increased, and at the Armistice we were manufacturing over 35,000 yards of balloon fabric per week, every piece of which was tested in Aeronautical Laboratories for weight, strength, and hydrogen leakage.

Our

The investigations of the Research Laboratory into the action of light on rubber resulted moreover, amongst other things, in a discovery which without any increase in weight permitted the production of a fabric of vastly enhanced durability, specially suitable for use in the tropical theatre of the war.

Our reason for asking the publication of this communication is only for the purpose of stating that at least one manufacturer was sufficiently well-equipped, not only in the manufacture, but in their scientific staff and laboratories, to carry on without outside help, and it is not intended to detract in any way from the very useful and great assistance which the National Physical Laboratory

gave to Government Departments and others starting out in what was probably new ground to them.--I am, &c.,

one

L. A. WILLIAMS (Works Manager)

THE NORTH BRITISH RUBBER CO., LTD.

NOTES.

to

BACTERIA OF THE HEVEA LATEX.-The microbes identified, in experiments by Messrs. Denier and Vernet, as existing in the latex of the Hevea are in number 27 aërobiotic, or facultatively so, and anaërobiotic. These bacteria belong numerous species. There is the Coccus in a cluster, chains or groups of four. The CoccoBacillus is represented by two species. Bacilli are very numerous, twenty of them were counted. Some have no peculiar characteristic, others are chromogenic and some have a median or terminal spore. These microbes were found irregularly in the various experiments except one which was isolated in all, whatever the medium adopted. It represents the bacteriological constant of this flora. Its biological properties are very extensive. It attacks dambosite which is the sugar of Hevea latex; it is the only microbe with this property. It ferments lactose and saccharose, coagulates milk, liquefies gelatin, but remains without action on coagulated egg albumen. These microbes attack lactose. Saccharose is transformed by 10 bacteria and also by the anaerobiotic bacillus. The microbes coagulating milk, except one, are very rare. The proteolytic power of these various bacteria was investigated with coagulated egg albumen and gelatin. White of egg is more 13 bacteria less completely digested by including the anaerobiotic bacillus, and particularly marked in the case of four. Finally, there are eleven which liquefy gelatin. The first series of experiments demonstrates that the microbial flora, chiefly acrobiotic, is extremely polymorphous. It is, however, to be noted that one microbe is found regularly in every case, and that it alone acts upon the sugars of the latex of the Hevea Brasiliensis which it tranforms into acids. Caoutchouc and La Gutta Percha, September 15, 1920.

or

MINERAL RESOURCES OF GREAT BRITAIN.-The Ministry of Agriculture and Fisheries desire to give notice of the publication of a second edition of the Seventh Volume of the Special Reports on the Mineral Resources of Great Britain, which have been prepared by the Director of the Geological Survey in response to numerous enquiries that arose through conditions brought about by the late war. Price 5s. net. In the second edition of this Memoir the account of mineral oil, and of the explorations now being made for it in Great Britain, is brought up to date of going to press (June, 1919). In the chapter on Kimmeridge oil the results of analyses made by the Mineral Resources Development Bureau, and further notes on the works in progress in Norfolk have been added. The records of occurrences of cannel coals have been greatly expanded, as a result of recent investigation in all the coalfields of England and Wales. Copies may be obtained, through any bookseller, from the Director-General, Ordnance Survey Office, Southampton.

THE FOUNDATIONS
OF CHEMICAL THEORY

An Introductory Textbook. By R. M. CAven, D.Sc• (London), F.I.C., Professor of Inorganic and Analytical Chemistry in the Royal Technical College, Glasgow. Royal 8vo. Price 12s. 6d. net.

A concise account is given in this book of the foundations on which the structure of modern chemistry is reared. The story is simply told with the essential technique. The book meets the needs of degree students in chemistry, who require a book introductory to the larger treatises on physical chemistry.

AND ITS PRACTICAL APPLICATIONS A Textbook of Electrical Engineering. By MAGNUS MACLEAN, D.Sc., Professor of Electrical Engineering, Royal Technical College, Glasgow. Fully illustrated. Demy 8vo, price 12s. 6d.

This book is designed to cover the subjects treated in a first-year course of Electrical Engineering. Special care has been taken to explain clearly the physical facts which underlie the action of all electrical machinery and appliances. Ease in calculating electrical quantities must be acquired by every electrical engineer, no matter what special branch he may take up, and to make the path as easy as possible for the student, a large number of worked examples and exercises, with answers, are given, and a special Appendix has been written explaining the Electrical Units employed in Engineering.

APPLIED OPTICS

THE COMPUTATION OF OPTICAL

SYSTEMS

Translated from the German of STEINHEIL and VOGT. BY JAMES WEIR FRENCH, B.Sc. In Two Volumes. F'cap quarto. Price 30s. net.

"... Mr. French has provided an excellent handbook, which we commend to the serious attention of every student of technical optics."-Philosophical Magazine.

METEOROLOGY

An Introductory Textbook. By A. E. M. Geddes, O.B.E., M.A., D.Sc., Lecturer in Natural Philosophy in the University of Aberdeen. (Ready Shortly.)

A concise and clearly written account of the modern science of Meteorology. A knowledge of the elements of the subject is now essential to air pilots, naval and military officers, and navigators; while the weather '' and the how and "why of its vagaries are full of

interest to everyone.

SCIENTIFIC METHOD

ITS PHILOSOPHY AND ITS PRACTICE

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TIDAL LANDS

A STUDY OF SHORE PROBLEMS

By ALFRED E. CAREY, M.Inst.C.E., Fellow of the Chemical Royal Geographical, Geological, and Societies, and F. W.OLIVER, F.R.S., Quain Professor of Botany in University College, London. Copiously illustrated with 29 full-page plates in addition to figures in the text. Demy 8vo. Price 15s. net.

"To the engineer, the subjects discussed in this work are of the greatest possible importance, and whether he may be interested in the facts here recorded from the point of view of river control. or of the reclamation of the foreshore, or of the arrest of sand-dunes, he will find much matter for serious thought and consideration, and many details likely to aid him in his undertaking."-Times Engineering Supplement. LIFE AND ITS MAINTENANCE

A SYMPOSIUM ON BIOLOGICAL
PROBLEMS OF THE DAY

The contributors include: W. M. Bayliss, F. G.
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Martin Flack, R. C. M'Lean, F. W. Oliver, H. M.
Vernon, Henry Kenwood, Price 5s. net.
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