The facts concerning this last particular chemical operation are taken as an example to show that, in each one of all the similar cases in this and other papers, the volume and alteration in volume of each one of the several elements concerned has been exactly discovered. The Mg-atom descends from vol. 27.71 to 7.16 thereby evolving 59190 calories. The two chlorine atoms remain unchanged. Each H.atom descends from volume 8.59 to 0.97, as explained in the paper on Active Hydrogen.

It is necessary to remember that each atom of Mg actually decreases in size in the proportion of 27.71 to 7.16; but that each atom does not evolve 59190 calories. a gram-atom that does this.

It is

The volume 7.51 is correct for 7 independent reasons:

(A1) It can be split up into two parts (No. 2) in accordance with the law of relative volume;

(A2-A6) It occurs five times in Table II., each of which is independent of the others;

(A7) It gives the same original volume as the other two values of H.F. in Table III.

Similarly, 8.71 is correct for eight, 13.69 for five, and 14.565 for six independent

reasons.

SUMMARY.

The intricate interdependence of facts demonstrated in this paper makes it absolutely certain that the correct interpretations of the varied phenomena have been deduced.

The only apparent flaw in the proof is the fact that the original volume of the element, required by the law of heat of formation, is double the volume obtained by experiment. But the fact that it is exactly double, and also that the same original volume is re quired in all three cases in Table III., proves without any doubt whatever that no flaw exists, but that the apparent discrepancy is due to something which has not yet been discovered.

The clue to this state of affairs happens to appear in an article in the Chemical News, 1925, CXXXI., 2, by Martin Meyer on the "Preparation of Zinc Diethyl," as follows: "Should the reaction fail to start, as occasionally happens, it may be necesary to distil all of the ethyl iodide over into B and reheat the zinc for a few minutes.' This means that the reheating of the zinc puts

of our

Applying this hint to the case present problem concerning Mg, and taking all the observed facts into consideration, it is evident that an atom of Mg in the metallic state normally has a relative volume of 13.885, i.e., one half of the element is completely absorbed by the other half (No. 9) But when heated the absorbed part is ejected, so that each atom has a temporary volume of 2(13.855) = 27.71.

In addition to demonstrating the structure of Mg by means of three sets of experimental data, viz., At.wt., S.G., and H.F., this paper accomplishes the following objects:

(B1) It continues the reduction of the experimental data of S.G. to exact instruments of research.

(B2) It strengthens the Law of Relative Volume.

(B3) It strengthens the Law of Heat of Formation.

(B4) It demonstrates the causes of Thomsen's observed experimental effects, not necessarily of his calculated effects.

(B5) It continues the demonstration that water of crystallisation absorbs heat when formed from liquid water, especially in Nos. 64, 65, and 66. (B6) It continues the demonstration that it is impossible to calculate the H.F. of any substance (as Thomsen did) with any certainty of its being correct without the previous knowledge of the relative volume of each atom forming the substance.

The structure of an atom of Mg by this and many previous papers is

General Notes.

THE COAL MINING INDUSTRY
IN RUSSIA.

The revival of the coal industry in the Union of Soviet Socialist Republics started about 1921, and developed to such an extent-much faster than the metallurgical industry that by 1924 large stocks had accumulated and output was greater than consumption, states Mr. P. Gent, of the British Mission in Moscow, in a report to the Department of Overseas Trade. Exports to Mediterranean countries and the Near East commenced in 1924 at prices below cost discontinuance of imports and a wide campaign for fostering the home consumption of coal, all failed to bring demand to the level of production. During the spring of 1925, output was therefore curtailed, shafts were closed, and workers dismissed. During the last month or two, particularly in view of good harvest prospects, symptoms have become manifest of a more rapid economic recovery, especially in industry even in the metallurgical industry, which is the most backward. June output of coal showed a marked increase over May, owing chiefly to the increased productivity of labour and partly to mechanical improvements. This increase, coinciding with the compiliation of bigger industrial output and increased railway traffic plans for 1925-26, has not aroused concern. On the contrary, it is declared that fuel demands next year will exceed the supplies foreseen by fuel plans. In June, 123,710 persons were employed in the coal mining industry.

ELECTRIC STORAGE BATTERY LOCOMOTIVE COMPETITION. Colonel G. R. Lane-Fox, M.P., Secretary for Mines, announces that the judges appointed to adjudicate on the above competition for a prize of £1,000 which was offered by Mr. Charles Markham, of Ringwood Hall, Chesterfield, for the best type of locomotive for use underground in coal mines, have arrived at their decision. They award the whole of the prize to Messrs. Joseph Booth & Brothers, Ltd., engineers, Union Foundry and Ironworks, Rodley, Leeds, whose design fulfilled the conditions of entry, and was, in their opinion, the best that was submitted to them.

The judges propose to present in due

at

of

U.S.A. TEXTILE IMPORTS: THE INCREASE IN RAW MATERIALS. Imports into the United States of textile fibres and of textiles during the fiscal year ended 30th June last were valued 971,645,000 dollars, an advance 101,000,000 dollars, or 11.6 per cent., over the total for the previous twelve months, states "Commerce Reports," the official journal of the Bureau of Foreign and Domestic Commerce branch of the United States Department of Commerce at Washington. The bulk of this increase is accounted for by larger purchases of textile raw materials abroad.

TAXES ON COMPANIES IN HUNGARY.

The British Commercial Secretary at Buda-Pest has forwarded a translation of a Decree (No. 400/P.M.), issued by the Royal Hungarian Minister of Finance relative to the consolidation of all legal regulations with regard to the Company Tax.

Foreign companies are subject to the same treatment and rate of tax as Hungarian companies. The various tax rates in force are enumerated in the Decree.

British firms interested may consult the Decree as translated at the Department of Overseas Trade, 35, Old Queen Street, London, S.W.1. (Reference 22638 F.W.)

BRITISH ASSOCIATION FOR THE
ADVANCEMENT OF SCIENCE.
Section B.-Chemistry.

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.)

When a liquid mixture of two substances which are miscible in the solid as well as in the molten condition, such as an alloy of copper and nickel or a fused mass of albite and anorthite, begins to solidify, the composition of the crystals has to adjust itself continuously in order to maintain equilibrium with the changing liquid phase, as was shown by Roozeboom in his classical work on solid solutions. Such an adjustment is only possible by means of diffusion, and when cooling is sufficiently slow, the adjustment does in fact keep pace with the change in the liquid, but with more rapid cooling the interior of each crystal differs in composition from its outer layers, there being a concentration gradient from the centre to the boundary. This condition produces the cored crystals which are familiar to every metallurgist, and the "zoned" crystals of the mineralogist. In most alloys this want of homogeneity disappears after a sufficiently long period of heating at some temperature below that of which the first drops of liquid are formed, but alloys of bismuth and antimony fail to become uniform even after weeks of annealing, whilst the felspars and similar minerals have never been persuaded to lose their zoned structure by any methods known in the laboratory.

occurs

Bruni has shown and Vegard has confirmed the observation by the X-ray method, that true interdiffusion between potassium and sodium chlorides when mixed and heated in the solid state. Electrolytic transport is observed in the solid halides of silver and in mixtures of silver and copper sulphides, but the modern view of the structure of such substances represents them as built up of ions rather than of neutral atoms, and this must be taken into account in any interpretation of the facts. The apparent absence of diffusion in minerals which have once solidified, even when given geological periods of time, is a serious difficulty in the way of any general theory of diffusion. Such ex

amples of the passage of alkali metals through quartz and other silicous minerals under the influence of a difference of electric potential are probably not instances of true diffusion at all, but merely of the passage of traces of impurities through a mass which is not completely impervious. We have always to bear in mind that crystals, whether of natural origin or prepared in the laboratory, are rarely perfect, and may contain cavities and capillary passages through which matter may pass without disturbing the crystalline lattice. This idea of the imperfection of crystals has found an interesting application in the work of A. A Griffith on the rupture of solids and of such semi-solid substances as glass and fused silica. The tensile strength of metals and of these substances is far smaller than would be expected from calculations of the theoretical cohesion of the materials. Griffith supposes that actual solids and glasses contain innumerable fine cracks, which reduce the strength. By special means he has been able to prepare rods of glass and silica in an unstable state, in which their strength and elasticity are enormously greater than in their normal condition. It has even been suggested that means may be found for bringing our ordinary metals and structural materials into a similar condition, which would enable them to withstand loads several times greater than those which are normally possible, although the prospect of a sudden return to the stable condition with its accompanying weakness may alarm the engineer.

However, the use of materials in an unstable conditions is already familiar to metallurgists. Hardened steel is an instance. At high temperatures the structure of most of our steels is homogeneous, the carbon being in solid solution in the iron, which is then in the y-condition. As the temperature falls, the iron changes into a modification which is stable at lower temperatures, and loses its power of holding the carbon or carbide molecules (for the X-rays have so far failed to determine how the carbon atoms are grouped in the space lattice) in solution, so that separation occurs, and a-iron and cementite, Fe, C, from the mass, two solid phases now being present in place of one. The scale of the separation may vary greatly according to the time occupied by the process. separation can occur without diffusion, and the transport of atoms or molecules through

No

the solid mass takes an appreciable time, which is greater the lower the temperature, so that it is much less perfect when the steel is cooled rapidly than when ample time for diffusion is permitted. Consequently, the size of the molecular aggregates of cementite may vary from that of ultramicroscopic particles, so small and offering so large a surface to the action of chemical reagents that the mass is stained black or brown by acids, in which case the mixture is known as trootsite, to the comparatively coarse, although still microscopic scale of the wellknown laminated pearlite, in which the thin alternate sheets of ferrite and cementite, like the fine sheets in mother-of-pearl, can produce colours by the diffraction of light, when the pearly appearance noticed by Sorby in the first exact scientific study of the microscopic structure of a metal.

a

Now let the cooling be so rapid that a distinct separation into two phases, even on an ultramicroscopic scale, does not occur. The rearrangement of the iron atoms in their space lattice, in this instance from the face-centred cubic arrangement of the y-iron into the body-centred cubic arrangement of a-iron, still takes place, but the crystallisation of cementite as separate phase is prevented. The result is that a new structure is obtained, known as martensite, in which the iron is, at least for the greater part, in the a-form, as is proved by its X-ray examination and by its magnetic properties, but in which the carbide is held, either in unstable solid solution in a-iron, in which it is normally insoluble, or as sheets of molecules parallel with the octahedral planes of the iron. Both views have their supporters, but I must profess a leaning towards the second. Whichever be correct, it is certain that this unstable condition is associated with great hardness and lack of plasticity, and it is necessarily present in fully hardened steels. Still more rapid cooling may suppress both the change in the lattice and the separation into phases, the solid solution which is stable at high temperatures being preserved during cooling, so that a part of the iron is still in the y-condition, and holds carbon atoms in a homogeneous fashion within its structure. As such a cooled solid solution is not hard, the steel is actually rendered less hard and brittle when the quenching is so severe than if it had been cooled somewhat less rapidly. The transformation of the iron, however, occurs with such ease that it is only when the proportion of car