ating against the surface of a rock already divided into small flakes by exfoliation has produced the notch that forms the neck. The neck is eccentric, and the greater overhang on the upstream side may be due to which this block has undoubtedly fallen. The rock apgreater wear on that side. pears also to have been slightly polished by the water and its contained suspended matter. The rocks described in the foregoing paragraphs are, so far as form alone is concerned, typical "mushroom" or pedestal rocks. They are composed of material of almost equal hardness from base to top, and have attained their form as the result of differential scour rather than differential weathering. Thus they differ in composition and origin from the pedestal rocks described in a previous publication. Save for the fact that these rocks occur in stream beds, they might be mistaken for rocks formed by wind scour. It is also entirely possible that rocks in arid regions formed by stream scour may have been mistaken for rocks formed by wind scour. Such confusion is the more likely in that the areas in which the examples cited in this paper occur have no great similarity in climate. Eastern Washington, in which the Devil's Top and the rock in Columbia River were formed, has a sub-humid or semi-arid climate, typified by that of Spokane, which has a mean annual precipitation of 18.85 inches and a cold winter. The Owen's River canyon lies in a warm arid region with an annual rainfall of only a little more than 5 inches. Yellowstone Park, on the other hand, has a cold humid climate. The character of the stream flow and the original form, position, and physical characteristics of the rocks are probably more influential than climate in producing these remarkable forms. NOTE. The rock in Gibbon River, Yellowstone Park, has also been described by E. A. Martel, who visited the locality with the International Congress of Geographers in 1912. His note, illustrated with three excellent photographs, was published in the Comptes Rendus des Séances de l'Académie des Sciences de Paris, vol. 159, pp. 87-89, 1914. Martel has also described a large number of pedestal rocks in other localities, which he attributes to the action of both surface and underground streams. General Notes. LONDON COUNTY COUNCIL'S GREAT EDUCATION SCHEME. Apart from its comprehensive elementary educational system, as exemplified in its elaborate chain of Board schools, throughout the Metropolis (and at which an excellent education is provided free of cost), the London County Council is also carrying on a great and beneficent work in the realm of higher education, including technical and electro-chemistry, chemical engineering, and many other branches of science and art, enabling the ambitious and assiduous student degrees and diplomas. Special attention is paid to chemistry, we as the oldest chemical paper are pleased to note. Needless to say, the County Council's efforts are duly appreciated by the London University, The Institute of Chemistry, and most other learned societies. Among the centres where higher instruction is given, are the Battersea Polytechnic, Battersea Park Road, S.W.11.; Borough Polytechnic, Borough Road, Mauresa S.E.1.; Chelsea Polytechnic, Road, Chelsea, S.W.3; City of London College, White Street, Moorfield, E.C.2; Hackney Institute, Dalston Lane, E.S.; Northampton Polytechnic, St. John Street, E.C.1; Northern Polytechnic, Holloway Road, N.7.; L.C.C. Norwood Technical Institute, Knight's Hill, S.E.27.; L.C.C. Paddington Technical Institute, Saltram Crescent,W.9.; Regent Street Polytechnic, W.1.; Sir John Cass Technical Institute, Jewry Street, Aldgate, E.C.3.; Wandsworth Technical Institute, High Street, Wandsworth, S.W.18.; Woolwich Polytechnic, William Street, Woolwich, S.E.18., Not only are these centres of higher education established throughout the Metropolis, but the L.C.C. provides by its elaborate tram service, excellent facilities at very cheap rates for reaching the said centres. May its good work prosper. etc. BRITISH SCIENCE GUILD. THE NORMAN LOCKYER LECTURE. The first annual Norman Lockyer Lecture, established by the British Science Guild as a means of periodically directing the attention of the public to the influence of science upon human progress, will be gievn by Sir Oliver Lodge, F.R.S., on Monday, 16 November, 195, at 4 p.m. The subject of the lecture will "The Link between Matter and Matter." Lord Askwith, K.C.B., K.C., President of the Guild, will be in the chair, and the lecture will be held in the hall of the Goldsmiths' Company (by kind permission of the Master and Court of Assistants of the Company). Tickets of admission may be obtained on application to the Secretary, British Science Guild, 5, John Street, Adelphi, London, W.C.2. It should be explained that the Dominion Water Power and Reclamation Service of the Department of the Interior is engaged in making a systematic survey of the water resources of the whole of the Dominion. A separate series of stream measurement reports is published for each of these four divisions, and these cover respectively the Atlantic drainage south of St. Lawrence river, including Nova Scotia, New Brunswick, Prince Edward Island, and Southeastern Quebec; the St. Lawrence and Southern Hudson Bay drainage (and Mississippi drainage in Canada) in Alberta, Saskatchewan, Manitoba, extreme Western Ontario, and North-West Territorities; and the Pacific drainage in British Columbia and the Yukon Territory. The report under review is one of the third series above described. It contains a short explanation of the purpose and scope of the work and two hundred and sixteen pages of tables and descriptions of gauging stations, with an index map of Alberta, Saskatchewan, Manitoba and Western Ontario showing their location. This report will be supplied free of charge on application to the High Commissioner for Canada, Canadian Building, Trafalgar Square, London, S.W.1., or to the Director, Water Power and Reclamation Service, Ottawa, Canada. CANADIAN PRODUCTS IN 1924. There was a slight advance in the production of talc and soapstone in Canada during 1924 according to the Dominion Bureau of Statistics. Sales for the year totalled 11,332 tons, worth $154,480, as against 10,366 tons, at $150,507 in 1923. Increases in both quantity and value were recorded in finally revised statistics on the production of silver in Canada during 1924 as reported by the Dominion Bureau of Statistics. The output reached 19,736,323 fine ounces, valued at $13,180,113, as against 18,601,744 fine ounces valued at $12,067,509 in 1923. The production of cheese in Canada in 1924 totalled 151,673,880 pounds, valued at $24,518,734 according to the Dominion Bureau of Statistics. Compared with the preceding year an increase of 49,504 pounds is shown in the quantity, but a decrease of over four million dollars in the value. The average price per pound was 16 cents in 1924 and 19 cents in 1923. The output of zine for the year 1924, as reported by the Dominion Bureau of Statistics was 98,909,077 pounds (49,455 tons) valued at $6,274,791, as against 60,416,240 pounds valued at $991,701. The increase amounted to 64 per cent. in quantity and 57 per cent. in value. This large increase was caused by the enlarged production in British Columbia. Quebec was the only other province to produce zinc; there an increase was reported of about two and a half million pounds. Canada's exports during 1924 included 12,772 motor trucks, 43,883 passenger automobiles, and parts valued at $4,992,049. giving an aggregate value of $31,501,442, according to the Bureau of Statistics. The quantity of creamery butter made in Canada in 1924 was 184,290,908 pounds valued at $63,449,160 according to the Dominion Bureau of Statistics. This production is the largest for any year in the history of the industry and exceeds the proThe value of the production shows an increase over that of the preceding year of six million dollars, and almost equals the value for the record year of 1920, the greater value in that year being due to the high average price per pound-57 cents, compared with 34 cents in 1924. THE ROYAL PHOTOGRAPHIC EXHIBITION. Photographers in France have this year celebrated what they regard as the centenary of their art, since a hundred years ago, or thereabouts, their countryman, J. Nicéphore Niépce produced photographs by utilising the hardening action of light upon bitumen fixed to a metal plate. The legitimate pride of the French, however, has perhaps obscured from their minds the earlier work (1802) of Thomas Wedgwood in with conjuction Sir Humphry Davy. (The essential steps in the historical progress of photography are "Brief given on pp. 131 et. seq. of my Outline of the History of Science," published by the Chemical News. An important article on Photomicrography, by E. H. Ellis, appeared recently in these columns.) It is, therefore, of interest to note that the seventieth annual exhibition of the Royal Photographic Society is now in progress, and will remain open at 35, Russell Square, W.C., until October 24. Admission is free, and the illustrated catalogue costs 1s. The October issue of the Society's Photographic Journal (price 1s. 6d.) is a special exhibition number, and contains a exhibits review of the by well-known authorities, and is fully illustrated. The photographs and exhibits are arranged in sections. The first comprises the pictorial prints, which are on view in the main room of the first floor. Many show that progress has been made in technique, and some are of a high order of merit. The majority of the exhibitors are Members or Fellows of the Society, but a few are from distinguished foreign photographers, including one from Czecho-Slovakia. Photographers now seem to find their most artistic and quaint settings on the continent, if the exhibition accurately reflects the actual trend of events. Perhaps, on the other hand, these may have been acquired whilst on holiday. The lantern slides also reflect the same tendency. Among the many of merit, mention may be made of "Damascus Gate," by A. Keighley; Andorra Vicella," by Bertram Park; "Re-conditioning the Victory" by Capt. E. J. Mowlam; "Noel Coward," by Miss Wilding; and "London," by A. G. Buckham. Many "cloudscapes" and sailing vessel photographs were also of high merit. The pictorial lantern slides illustrated scenes in Spain, France, Italy, and a few of provincial England, etc. The scientific and technical slides are chiefly of natural history subjects, but a few illustrate the developments in photomicrography. The Royal Aircraft establishment has contributed some good examples of aerial photography, and the International Western Electric Co., some photographs transmitted by telephone. Demonstrations of Kinematography were given with the Pathé Baby Cine Camera; Messrs. Chance Bros. exhibited various types of optical glass as used for photographic lenses. Zinc crown glass represents the latest perfections in this work. Ross's also exhibited lenses, and Ilford's had an exhibit to illustrate the use of the panchromatic plate. This exhibition constitutes an annual event of interest to all connected in any way with photography. J. G. F. D. BRITISH ASSOCIATION FOR THE THE CHEMISTRY OF SOLIDS. ADDRESS BY PROFESSOR CECIL H. DESCH, D.Sc., Ph.D., F.R.S., President of the Section. (Continued From Last Week.) Of metallic alloys other than steel, the number of possible combinations is so large that only a minute fraction has been investigated. So far there is no rule by which we can mark out, in the neighbourhood of each metal in the periodic classification, a region within which useful alloying constituents may be found, but it is probable that further work will indicate such a possibility. The modification in the properties of a metal brought about by alloying depends largely on the formation of solid solutions, and when these vary in concentration with change of temperature, that is, when one or other constituent partly separates from solution on lowering, or sometimes on raising, the temperature, there is a possibility of changing the properties of the alloy by suitable thermal treatment. To a large extent this possibility has been neglected in respect of non-ferrous alloys, but experience with the light alloys of aluminium has shown how important such effects may be. Duralumin, which is composed of aluminium alloyed with copper and magnesium, was first found to vary in mechanical properties when its thermal treatment was altered, and its behaviour, which is shared by some other alloys of aluminium, has been explained on the basis of observations made chiefly at the National Physical Laboratory and at the U.S. Bureau of Standards. It appears that certain of the constituents of these alloys, especially magnesium silicide, Mg,Si, and the compound CuAl2, are more soluble in the solid metal at high temperatures than at low, and that their state of aggregation in the cold alloy depends on the rate of cooling. When first separated from solution, these compounds are dispersed in a condition of ultramicroscopic fineness, but when sufficient time is allowed, diffusion enables them to form larger and larger particles, there being a certain degree of dispersion which is associated with the best mechanical properties. In light alloys, as in steel, the degree of dispersion of one of the solid phases throughout another plays a great part in determining the properties of the composite mass. In this respect alloys resemble colloidal systems, and analogies may be found between the two, but nothing is gained by representing metallography as a branch of the chemistry of colloids, and certainly nothing by the restatement of familiar metallographic facts in terms of the formidable nomenclature with which that important branch of chemistry has been saddled by some of its enthusiastic advocates. Metallographic structure is essentially a matter of the distribution of solid phases in a system, and the scale of subdivision of one of the phases, although of immense practical importance, is not a factor which alters the fundamental character of the relation between components and phases. The theoretical part of metallography by means of which we interpret the thermal and microscopical observations of the laboratory is based on the doctrine of phases of Willard Gibbs. The purely thermo-dynamical treatment is, however, too abstract, and it is the simple temperature concentration diagram which is invariably used to represent equilibria in alloys, igneous rocks, or such artificial mixtures as cements. Only rarely is it necessary to appeal to the formal statement of the phase rule, most of the systems being simple enough for the number of possible phases at a given temperature to be obvious on inspection, whilst the vapour phase may usually be neglected. Systems of three components are represented by a three-dimensional model on a triangular base or by sections through the model, or by projections on to its base. For four components, the tetrahedral model is used, mainly in the form of sections, whilst for systems of greater complexity several devices have been proposed, but the study of alloys and mineral mixtures has scarcely progressed so far as to have made any serious demand for them. In time to come, both the metallurgist and the petrologist will need a means of representing such complex examples, but that stage will be reached by gradual steps. Allotropy of the dynamic kind represents difficulties, but it is not yet certain that the rather abstruse treatment adopted by Smits is necessary to its study, although evidence is accumulating that two allotropic forms may co-exist over a range of temperature within a solid, equilibrium only being attained with great difficulty. The metallurgist and the chemist interested in cements or other silicate mixtures has continually to bear in mind that he is dealing with systems which are not easily brought into equilibrium, and that for many practical purposes they are deliberately used in an unstable condition, persisting on account of the great resistance to movement within a solid, to which I have already referred. The equilbrium diagram serves as a guide, even to metastable systems, if the diagram be used to indicate the phases which may be expected to appear when undercooling occurs, and due use is made of the knowledge of undercooling which we owe to Miers and to Tammann. This is a most interesting branch of metallography, the theory of which is in course of development. Bowen, of the Geophysical Laboratory at Washington, has proposed another manner of studying the order of crystallisation in the liquid and solid states in mixtures of high viscosity, such as igneous rock magmas, and it is on the wonderful experimental work of that institution that the modern study of silicates on lines similar to those which have served so well in metallography is based. Bowen's reaction principle has to be reconciled with the theory of undercooling worked out for salts by Miers and for glassy materials by Tammann, and applied with success to steels by Hallimond. Meta stable or labile conditions may persist indefinitely when the viscosity of the system is great enough, hardened steels and prehistoric bronzes having undergone no perceptible change in structure in the course of centuries although Barus and others have shown that a secular change in the electrical resistance may be detected in steels, indicating a very small amount of reversion to the stable condition. Chemical reactions in the midst of a solid may be prevented from reaching equilibrium by the formation of a layer of the solid product between two reacting substances. When a layer of this kind has been formed, further reaction is only possible by diffusion of atoms through it, and it will evidently depend on the closeness of packing of the molecules in that layer whether diffusion is easy or difficult. As a rule, it is probably more difficult than in the original solid, and we therefore find on microscopical examination that crystals of the two reacting sustances, whether pure metals, solid solutions, or intermetallic compounds are separated by a zone consisting of the product of reaction, which may be very persistent, although its breadth gradually diminishes on annealing. This effect is well seen, for instance, in alloys of copper with antimony. An interesting class of reactions is that which includes the decomposition of a crystalline solid, one of the products escaping in the form of a gas whilst the other remains solid. From the nature of the curves connecting decomposition and time Hüttig and others have concluded that the escaping molecules must be able to traverse the crystal freely without serious dislocation, but this view is not confirmed by examination by means of X-rays or in any other independent manner. On the other hand, Hinshelwood has examined a number of reactions in detail, giving special attention to the physical condition of the crystals before and after decomposition, and his experiments are not only of a higher order of accuracy but they include a study of the physical conditions of the reaction. The decomposition of the permanganates by heat has been found to be a convenient one for this purpose, since it procees at a moderate temperature, and the reaction is undoubtedly monomolecular. The initial rate of decomposition of silver and potassium permanganates is greatest when the solid is finely powdered, but when crystals of appreciable size are used, the decomposi tion proceeds at an accelerated rate, as the crystals become disintegrated. The results prove that the reaction is confined to the surface, and that it can only proceed inwards as the texture is loosened, so that diffusion does not play a part in the process, at least when the temperature is such that the decomposition is nearly complete in an hour or two. When solid solutions of potassium permanganate in potassium perchlorate are used, the latter salt being stable under the conditions of experiment, the rate of decomposition is lessened, the observed effect corresponding closely with that which is calculated from the heat of formation of the solid solution, a quantity which has been directly determined. Some similar decompositions are more complex owing to the catalytic effect of one or other of the products of reaction. The hindering effect of a solid coating, already referred to in connection with reactions in the interior of metallic alloys, is seen in the decomposition of ammonium dichromate by heat, large crystals becoming coated with an adherent layer of chromium oxide, which retards further decomposition. Very recently Kurnakoff has studied the gradual change in the state of oxidation and hydration of vivianite, an hydrated ferrous phosphate. When first produced, these crystals are colourless, but they become blue as oxygen is absorbed, a part of the iron passing into the ferric state. Moreover the degree if hydration may vary as water is taken up from without. During these changes it is stated that the structure of the mineral remains unaltered and the crystals remain homogeneous, the optical properties varying continuously, but it does not appear from the abstract that any X-ray examination has been made. Such behaviour recalls that of the zeolites, the structure of which is probably loose. It is unlikely than any closely packed crystal could behave in this way. A new field of investigation has been opened up by Tammann in his attempts to determine the arrangement of the atoms in solid solutions by purely chemical means, by studying the action of chemical reagents on the solid. It is a familiar fact that the 'parting of silver and gold in assaying, which consists in dissolving out the silver from the alloy by means of nitric or sulphuric acid, is only possible when the silver forme more than 60 per cent. of the alloy. When gold is present in excess of this proportion, then only a little silver is removed from the surface, and the action then comes |