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more thoroughly carbonised, the central core became blocked with pitch and tar distilled forward into the coal mass, and the gas and tar vapour being in this latter stage forced to find their way through the outer shell of red-hot coke, became degraded to the utmost limit, and gave very large volumes of such permanent gases as hydrogen mingled with methane, the least easily broken up of the hydrocarbons, the result being that the modern tar is in reality a mixture of low temperature and very high temperature tar. Such a tar, obtained from a good gas coal, will contain approximately :

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It is found in practice that the carbonisation under the ordinary gasworks conditions of a ton of good bituminous coal yields about one-third of a gallon of toluene from tar and gas.

In practice, the withdrawal from the gas of all the hydrocarbons that can be scrubbed out by creosote oil would reduce the heating value of the gas to a considerable extent, and various methods of getting over this trouble have been proposed, such as enriching the scrubbed gas by the benzene and xylene from the crude benzol after separation of the toluene by fractional distillation, or by so scrubbing the original gas that only about onethird of the crude benzol is withdrawn, as by such means the calorific value of the gas can be maintained at or above the statutory minimum of 500 British thermal units.

The tar and gas made in small country works as a rule contain more aromatic hydrocarbons than the products from large works, as the temperatures used in carbonisation are not so high; and should the Government need still larger quantities of toluene and carbolic acid for nitration, the gasworks of the Empire could treble the output by reverting to the temperature and methods employed before the introduction of regeneration in the furnaces. This, however, would reduce the gas yield from the 13,000 cubic feet per ton now aimed at by the gas manager to 10,000 cubic feet, but the higher calorific value of the gas would allow of the volume being made up by the addition of blue water gas.



N a course of lectures delivered at the Cavendish Laboratory during the Michaelmas term of 1886, Sir J. J. Thomson examined the dynamical result of assuming the passage of electricity through a metal to be of the same nature as through an electrolyte. The subject was dealt with more completely in "Applications of Dynamics to Physics and Chemistry" in 1888. The later discovery of the electron which might act as a carrier of electricity from molecule to molecule placed the idea on a much firmer footing, and in 1898 Riecke developed theories of the electrical and thermal conduction and thermo-electrical properties of metals, based on the existence between the molecules of carriers of positive and Two years later Drude negative electricity. worked out more systematically theories founded on the same basis, and it is his work which is usually quoted in accounts of electronic theories, generally with the simplification that only one type of carrier-the negative electron-is taken as These moving freely between the molecules. electrons are supposed to be produced by the dissociation of the electrically neutral metal atoms, what remains of the atom being left positively charged.

The moving electrons are assumed to have the same average kinetic energy as a molecule of a gas enclosed in a cavity in the metal would have. The nature of the impact of electron on metal atoms is not discussed, but as the motion of each metal atom is likely to be comparatively small, the gas laws which hold for the motions of the molecules of a light gas amongst those of a much heavier are applied and the electrons are said to have a mean free path of length λ. The motions are distributed in all directions equally, and the electrons cannot escape through the surface of the metal unless their speed perpendicular to the surface exceeds a certain limit. The action of ultraviolet light on the surface facilitates the emission.

When an electromotive force is applied to the metal there is superposed on this to and fro motion of the electrons a drift up the electric field, the relation of which to the field is such that the specific conductivity of the metal is proportional to nλ/T where n is the number of free electrons per cubic centimetre and T is the absolute temperature of the metal. Since the electrical conductivity of a pure metal is known to vary approximately inversely as the absolute temperature, this implies that nλ must vary inversely as ✔T. As there is nothing on the one hand to suggest so considerable a change of the free space between the metal atoms with temperature, while on the other the facts of thermoelectricity are against any considerable decrease in the number of electrons per c.c. as the temperature rises, it sems difficult to reconcile the law of variation of na with experimental facts.

If a slope of temperature exists in a metal, the

electrons coming from the hotter side of a cavity between two metal atoms will move more rapidly than when coming from the colder. There will therefore be a drift of energy towards the colder metal which bears to the slope of temperature such a relation that the heat conductivity of the metal is proportional to nλT. As the heat conductivity of a pure metal changes very little with change of temperature, this equation again implies that nλ varies inversely as T, and we have the same difficulty in understanding how this is brought about. On dividing the heat conductivity by T times the electrical conductivity the product nλ disappears from the result, and we obtain a constant the value of which should be approximately 23 × 108 for all metals at all temperatures. At air temperatures the values found experimentally vary between 2 and 3 × 108, and at very low temperatures between 15 and 3 x 108. The agreement between the two results is undoubtedly good, but when the calculations are improved in accuracy by taking into account the variation of the speeds of the electrons about the mean value used by Drude, Lorentz finds the constant 15 × 108, which is not in such close agreement with experiment. For alloys and conducting salts the experimental values are considerably higher than for pure metals, and Koenigsberger and others have put this down to the part played by the atoms themselves in the conduction of heat. For quartz and other electrical insulators which are good conductors of heat there can be no question of the insignificance of the rôle of the free electrons.


Owing to the different values of the concentration n of electrons in different metals, there will be a flow of electrons through the surface of contact of two metals till the potential difference produced stops the flow. In an unequally heated metal the same process of compensation will In the former case we get the Peltier and in the latter the Kelvin effect. The former agrees in order of magnitude with the values found by experiment, but as Sir J. J. Thomson has pointed out, it is difficult to reconcile the great decrease of electrical conductivity of a metal on melting with the small Peltier effect between solid and molten metal. The calculated Kelvin effect shows that the concentration n of the electrons must in all metals be nearly proportional to T, a result which is not easily reconciled with that for na deduced from the electrical or thermal conductivity.

Since a negative electron in motion in a magnetic field is acted on by a force transverse to its path, the theory affords a simple explanation of the Hall effect, and gives the right sign and order of magnitude for the effect in bismuth at ordinary temperatures, but the wrong sign for the effect at low temperatures, and for the effects at ordinary temperatures in iron and antimony.

In no field can the simple electron theory be said to have given a satisfactory quantitative account of the facts, and its elaboration in one region has in general led to greater difficulties in others. The kinetic energy of the electrons it

postulates is so great that an increase of 1° C. in their mean temperature involves a supply of heat ten times the specific heat of the metal. After pointing this out Sir J. J. Thomson, in 1907, in his "Corpuscular Theory of Matter," developed a new theory which may be called the doublet theory. According to this theory the atoms of a metal are grouped together in pairs, one of each pair positively, the other negatively charged. In ordinary circumstances the axes of these doublets point in all directions on the average equally. Under the action of an electric field the doublets tend to arrange themselves in lines, with the positive end of one near the negative of the next and electrons may pass from the negative end of one doublet to the positive of the next, and so along the line of doublets.

On the assumption that the axis of the doublets distribute themselves according to the gas law, that their centres are spaced on the average b apart while the charges of the same doublet are d apart, and p electrons are discharged from a doublet per second, the electrical conductivity of the medium works out proportional to nbdp/T where n is the number of doublets per c.c. and T the absolute temperature. The experimental facts show that nbdp is independent of temperature. In the same way the transport of kinetic energy by an electron leaving a doublet at a higher, and joining one at a lower temperature, leads to a heat conductivity proportional to nbp, which the experimental facts show is independent of temperature. The quotient of the heat conductivity by T times the electrical conductivity on this theory comes 2.6b/d × 108, and as b/d must be greater than unity the agreement with the experimental value 2 to 3 x 108, is about as good as in the case of the simple theory. The presence of the b/d makes it possible to include in the theory those substances for which the quotient is high.

At the junction of two metals the excess flow from one metal will cause a difference of potential and an electric field which will change the orientation of the doublets until the flows are equalised. In an unequally heated metal the same method of compensation will come into play, and we have the Peltier and Kelvin effects.

If the rotation of a doublet in an electric field does not take place about the middle point, the two charges of the doublet move with different speeds. If they are in a magnetic field its action on them will tend to incline the axis of the doublet to the plane containing the two fields, and there will be a flow of electrons at right angles to both fields. The direction of the flow will be determined by that of the end of the doublet which moves most quickly. We thus have an explanation of the Hall effect, whether it be positive or negative.

No numerical comparisons of theory with experiment appear to have been made in the case of these thermo-electric and thermo-magnetic effects.

In his addresses to the Institute of Metals on May 5, and to the Physical Society on June 25, Sir J. J. Thomson dealt with the modification of

his theory necessary to bring it into line with the discovery by Prof. Kamerlingh Onnes that at very low temperatures-4° or 5° absolute-the electrical conductivities of metals become infinite. The external electric field applied to the metal is assisted in bringing the axes of the doublets into line by the field produced by those doublets already in line. The kinetic energy of thermal motion of the doublets tends to destroy the alignment. At ordinary temperatures it is sufficient to destroy the alignment so soon as the external field is withdrawn, and the flow of electrons from doublet to doublet is stopped. But at very low temperatures the energy is not sufficient to modify an alignment once produced, and the flow of electrons continues when the external field is withdrawn. The conductivity in these circumstances will be very high.

From this short account of the present position of the two theories it will be seen that the doublet theory of Sir J. J. Thomson has shown a greater power than the electron theory of co-ordinating the facts of experiment. It has difficulties of its own, both in the nature of its fundamental assumptions and in its power of reproducing the facts quantitatively. It does not appear to provide electrons for emission by incandescent bodies, and in its latest development it involves serious changes not previously suspected in the thermal, thermomagnetic, and thermogalvanic properties of metals at the very low temperatures attained by Prof. Kamerlingh Onnes. But the great flexibility it has shown justifies a more generous treatment of it by those authors and lecturers who have been content to limit their exposition of these questions to the older electron theory. C. H. LEES.



HE safeguarding of our water supplies is of particular importance at the present time, for there may be considerable risk of pollution if typhoid and cholera cases or "carriers" arrive in any number from the seats of war, as may well be the case. The research work carried out by Dr. Houston is therefore of much value and is summarised in a Report just issued.1

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Dr. Houston first deals with his "excess lime method of purification. The hardness of water is chiefly due to bicarbonate of lime (temporary) and sulphate of lime (permanent), the former being kept in solution by the carbonic acid present. In the softening of water lime is added and combines with the free and semi-combined carbonic acid, causing a precipitation of the lime added and of the bicarbonate of lime in the water in the form of the relatively insoluble carbonate of lime. water treated with the right amount of lime has no caustic alkalinity and has practically no action. on the bacteria present. When more than enough lime is added the water is rendered caustically


1 Metropolitan Water Board. Eleventh Report on Research Work, together with Index to Research Reports, Nos. i-x inclusive. By Dr. A. C. Houston. Pp. vii+52. (London: Metropolitan Water Board, n.d.) Price zs. Ed.

alkaline and becomes actively bactericidal. Such a water would, however, be unfit for domestic and trade use, but if the excess of lime present be removed by the addition of a sufficiency of water from which the bacteria have been removed, the whole of the mixed water will be softened and purified, and will be satisfactory for all purposes. Dr. Houston has previously shown that if raw river water be stored for from four to five weeks the great majority of the bacteria are removed, and the water is rendered safe for drinking purposes. The excess lime method of purification consists, then, in the addition of an excess of lime, storage of the alkaline water for a day or thereabouts, so that the bactericidal action may be exerted, addition of a sufficiency of water, purified by storage, to neutralise the excessive alkalinity, and filtration to remove the precipitated carbonate of lime.

Dr. Houston has tested the method on a large scale at Sunbury and at Aberdeen. At Aberdeen Bacillus coli (which may be taken as an index of pollution) was present in the untreated water in from I c.c. to 100 c.c.; after treatment it was not found in 100 c.c.; the process is therefore efficient and it is comparatively inexpensive.

Another research which has been carried out by Dr. Houston is an investigation of "water microbes" giving the cholera-red reaction after incubation of cultures for twenty-four hours. The cholera-red reaction (obtained by adding acid to a culture) is a very constant and characteristic reaction of the cholera microbe, and as this organism is frequently conveyed by water, it is important to know whether water organisms other than cholera yield the reaction. It is satisfactory to find that, although eighty microbes out of approximately 1885 sub-cultures gave the cholerared reaction on first being tested, they were easily distinguished from cholera by the application of two or three further simple tests.

Dr. Houston is to be congratulated on the valuable research work he has been able to carry out in the midst of a vast amount of routine work. R. T. HEWLETT.


THE LATE PROF. J. COOK WILSON. EATH has of late been busy among Oxford residents. The demise of John Cook Wilson, Wykeham Professor of Logic, was not unexpected, for he had been in bad health for more than a year, and indeed had never recovered completely from the shock of his wife's death in January, 1914. January, 1914. Cook Wilson was a man of quite exceptional attainments. Born at Nottingham and educated at Derby School, he matriculated at Oxford in 1868. As scholar of Balliol he took no fewer than four first classes, two being for mathematics and two for classics. These were followed by the Latin Essay, the Conington Prize, and a fellowship at Oriel. After his election as Wykeham Professor he became a fellow of New College, but his affection for Oriel never waned, and his connection with his old college was of late


years renewed by an honorary fellowship. lectures and less formal courses of instruction were keenly appreciated, and his influence on the philosophical and logical studies of Oxford was very great. His published works, though giving evidence of much learning and critical acumen, were not copious in relation to the width and depth of his erudition. Cook Wilson was a man of strong views. These he was always ready to maintain with an eagerness and occasional vehemence which amused, but never offended, his interlocutors. His controversy with Archer Hinde over the Timaeus of Plato gave occasion for a display of fighting qualities which is still remembered in Oxford with sympathetic appreciation. He was not only a finished classical scholar, but also an accomplished mathematician; and to these attainments he added an unusually complete knowledge of German language, literature, and philosophy. One of the subjects to which he had devoted attention was the difficult problem of Greek music. On this he held views which did not coincide with those of many of the recognised authorities, in particular of the late Provost of Oriel, D. B. Monro. It must be confessed that he had his foibles; among them a somewhat deficient sense of proportion, especially in respect of time. But these in no way interfered with the regard in which he was held for the sterling worth and simplicity of his character. "The Cooker," as he was affectionately styled by his pupils and many of his colleagues, was an enthusiastic volunteer. He did much to keep alive the interest in military matters which in the days before the Boer war showed signs in Oxford, as elsewhere, of a dangerous slackening. He was practically the creator of the cyclist contingent of the O.U.V., and his manual of training for that body became a model for the cyclist service throughout the army. Many will remember "Das Kochmannslied," a piece of good-natured banter by H. W. Greene, of Magdalen, in which humorous reference was made to Wilson's military prowess, his famous manœuvre for the discomfiture of hostile cavalry, his "gyrotwistive Knasterbart," and his polemic with Archer Hinde. "Multis ille bonis flebilis occidit.


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WE are officially informed that Prof. H. B. Baker will be unavoidably prevented from attending the Manchester meeting of the British Association, and that, in his place, Prof. W. A. Bone will be the president of the Chemistry Section.

THE following additional information has reached us with reference to the communications which may be expected to be made to Section B of the forthcoming meeting of the British Association :-Prof. P. Henry (Louvain), vinyl acetic nitrite; Dr. A. Hynd, configuration in the sugar group; Dr. Sand, a new cadmium vapour arc lamp; Dr. W. E. S. Turner, ionisation in solvents of low dielectric constant; Dr. Turner and Mr. Cauwood, molecular state of salts in solution; papers on flame and combustion, with experimental illustra

tions, probable contributors, Prof. Dixon, Dr. Wheeler. and Dr. Coward.

A MUNITIONS inventions branch of the Ministry has been constituted, with Mr. E. W. Moir as comptroller. The branch, which for the present is located in Armament Buildings, Whitehall Place, will have the duty of considering projects for inventions relating to munitions for warfare on land or matters appertaining thereto. The comptroller and staff of the branch will be assisted in their work of examination, and, if thought necessary, in the investigation and development of any projects that may be considered worthy of being developed, by a panel of honorary scientific and other experts. The following have accepted Mr. Lloyd George's invitation to act on this panel :-Col. Goold Adams, Mr. Horace Darwin, Mr. M. Duckham, Mr. W. Duddell, Dr. S. Z. de Ferranti, Dr. R. T. Glazebrook, Sir R. Hadfield, Dr. J. S. Haldane, Col. N. B. Heffernan, Sir A. Kennedy, Mr. F. W. Lanchester, Dr. A. P. Laurie, Prof. Vivian B. Lewes, Mr. M. Longridge, Mr. W. H. Maw, Sir Hiram Maxim, Capt. Moore, Sir. H. Norman, Mr. F. G. Ogilvie, MajorGen. G. K. Scott-Moncrieff, Mr. W. Stokes, Mr. J. Swinburne, Sir J. J. Thomson, Mr. A. J. Walter, Mr. C. J. Wilson. All communications should be addressed to the Comptroller at the address given above.

THE President of the Board of Agriculture and Fisheries has appointed a committee (consisting of Lord Middleton (chairman), Mr. Henry Chaplin, Sir Ailwyn Fellowes, the Hon. Alexander Parker, Major Sir M. Burrell, Bart., Sir G. Greenall, Bart., and Capt. M. S. Adye) to consider and advise the Board as to the steps which should be taken to secure the production and maintenance in England and Wales of a supply of horses suitable and sufficient for military purposes, especially on mobilisation. Mr. E. B. Wilson, of the Board of Agriculture and Fisheries, has been appointed secretary of the committee.

It is reported from Stockholm that the Nobel prizes for the present year will amount to 8100l., but that the distribution may be postponed. From next year the prizes will be reduced by 1125l., representing the amount of the new Swedish defence tax.

THE sum of 140l. has been given to the Royal Society of Arts by Mr. R. Le Neve Foster for the purpose of founding a prize in commemoration of his father, Mr. Peter Le Neve Foster, who was secretary of the society from 1853 to 1879. The council has decided to offer the prize (consisting of 10l. and the society's silver medal) for a paper on “Zinc: its production and industrial applications." Competing papers (which must be typewritten) must reach the secretary of the Royal Society of Arts by, at latest, December 31, 1915.

ACCORDING to a Reuter telegram the Vienna Academy of Sciences has made a grant of 160l. to Prof. R. Poech to enable him to conduct anthropo

logical researches among the various races comprising the Russian prisoners of war.

WE learn from Science that Prof. W. H. Welch, of the Johns Hopkins University, and Dr. S. Flexner, of the Rockefeller Institute for Medical Research, are

about to inspect and report upon the medical schools and hospitals of China, on behalf of the China Medical Board of the Rockefeller Foundation.

We see from Science that an expedition has been sent by the St. Louis University to study tropical diseases and biology in British and Spanish Hon

duras. The expedition consists of Dr. J. P. Coony, professor of chemistry; Dr. E. N. Tobey, instructor in tropical diseases; and A. M. Schwitalla, a student in biology.

We regret to announce the death of Mr. Robert Hammond, a short account of whose career is given in Engineering for August 13. Mr. Hammond was one of the pioneers of electric lighting in this country, and was the first concessionaire of the AngloAmerican Brush Electric Light Corporation, Ltd. He was also associated with Messrs. Greenwood and Batley in the manufacture of electric machines, and put down the first works in this country in which current was distributed from a centre for lighting at high tension by incandescent lamps. Mr. Hammond put down electrical supply works in a great number of towns in this country and abroad. He was an ardent exponent of municipal trading; his services were often requisitioned as an expert witness. By reason of his kindly disposition and genial manner he established friendly relations with all with whom he came in contact, and his loss will be widely felt and deplored by his host of friends in all parts of the country. He contributed many papers for technical societies; in 1902 he succeeded the late Prof. Ayrton in the capacity of honorary treasurer of the Institution of Electrical Engineers, a position which he held until the time of his death. He was also a member of the Institution of Civil Engineers and of the Institution of Mechanical Engineers.

THE death of Mr. Edwin Charles Carnt is announced in Engineering for August 13. Mr. Carnt took up active work in the firm of the late Mr. John S. White at Cowes in 1898, a time contemporaneous with the almost world-wide recognition of the immense potentialities of torpedo craft. His experience as an officer in the Navy, as a member of the engineering staff of the dockyards, and as an overseer in private works, together with his personal qualifications, marked him out as an appropriate engineering manager of such works as White's. The firm, under his dominating energy and wide practical experience, quickly stepped into and retained a high place among the constructors of high-speed light craft of all types. His death took place on the 5th inst.

We regret to have to record the death, on August 16, at the age of seventy-seven years, of Mr. F. Victor Dickins, C.B., who was registrar of the University of London from 1896 to 1901.

PARTICULARS are given in the Morning Post of Monday last concerning Capt. E. Bage, of the Australian Engineers, who was killed in action at Kaba Tepe some weeks ago. In 1911 he joined Sir Douglas Mawson's Australasian Antarctic Expedition, making

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a record of tidal observations at Adelie Land. In the summer of 1912-13 Capt. Bage led his two comrades -F. H. Hurley (now serving with Sir Ernest Shackleton) and E. N. Webb (magnetician)-within fifty miles. of the south magnetic pole. On the journey back to winter quarters they failed to find a food depôt, but During the second year of enforced wintering Capt. got back to safety after nine weeks of great hardship. Bage turned his attention to magnetic work and astronomy, and made further valuable additions to Antarctic science.

A REUTER message from Zurich states that the Laryngologists' Society has expunged the name of Sir Felix Semon from the list of its honorary members, the reason given being that, although Sir Felix was born in Germany, and studied in Vienna and Berlin, he wrote a letter to the Times expressing detestation of the barbaric methods of the Germans in the war.

THE summer meeting of the Royal Cornwall Polytechnic Society will be held at Falmouth on August 31 and September 1 and 2, when the following communications will be made :-On August 31, "The Physical Condition of Cassiterite in Cornish Mill Products," by the late J. J. Beringer, further explained by W. H. Trewartha-James; on September 1, "The Occurrence of Tin and Tungsten in the West of England," by J. H. Collins; "Development of Mechanical Methods in China Clay Mines," by J. M. Coon; and 'Prospects for Tin in the United States," by H. F. Bain. On September 2 a paper on "Piskies: a Folklore Study," will be read by H. Jenner, and a lecture on "The Fly Problem," delivered by F. Balfour Browne. A feature of the meeting will be a display of exhibits illustrating British articles of commerce previously either wholly or partly supplied by Germany and Austria.

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THE provincial sessional meeting of the Royal Sanitary Institute will be held at Brighton on September 3 and 4, when discussions will take place on Indian sanitation, camp sanitation, maternity and child welfare, and on the final report of the Royal Commission on Sewage Disposal.

WHEN the Institution of Electrical Engineers has been able to arrange the various historical specimens of apparatus which it has collected for its museum, it will possess one of the most interesting collections of this character. The latest addition has been made by H.M. Queen Alexandra, who has given the institution a pair of Bell telephones presented to her in 1878, and made on board H.M.S. Thunderer. These instruments were actually used for conversation between the schoolroom and her Majesty's sitting-room at Marlborough House for a number of years. The Institution of Electrical Engineers is situated on Victoria Embankment, and it is therefore quite appropriate that it should possess the original Gramme dynamo used for the first experimental lighting of the Thames Embankment. There is also in the collection one of the Jablochkoff candles used in those days, and we believe that, to make this part of the collection complete, one of the holders employed for these

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