CHEMICAL NEWS, April 13, 1911

Experiments were also shown illustrating the ease with which a bridge containing an electrolytic cell could be balanced by placing a variable self induction in series with the cell and adjusting it and the resistance of the bridge simultaneously, as in Wien's experiments, except that a vibration galvanometer was used in place of the optical telephone originally employed by Wien.

The author's deduction from his experiments, that the resistance of an electrolyte varies with the frequency of the alternating E.M.F. applied, was discussed by Messrs. CAMPBELL, DUDDELL, LOWRY, F. E. SMITH, and the SECRETARY.

A paper on the "Oscillatory Currents in Coupled Circuits," was read by Prof. G. W. O. Howe.

A demonstration was given by means of a double projection oscillograph of the currents in coupled oscillatory

circuits. Each circuit consisted of a condenser, an aircore choking coil, and a strip of the oscillograph.

The condenser in the primary circuit was charged and discharged by means of a commutator on the spindle of the oscillograph motor. The two circuits may be taken to represent the condenser circuit and the aerial of a wireless telegraph sending apparatus, the frequency being two or three hundred instead of a million. The currents in the two circuits can be studied, and every change due to a variation in the damping of either circuit or in the coupling between the two circuits can be followed. This was illustrated by a series of typical photographic records.

A third oscillatory circuit may be taken to represent a wave-meter, and used to plot resonance curves, from which the damping can be calculated, as is commonly done in radio-telegraphic work. Here, however, we have the great advantage of knowing the damping accurately, and thus being able to check the resonance curve results under various conditions.

By altering the connections the conditions of the quenched spark sending apparatus, as used by Max Wien, Lepel, &c., was represented. Here the primary circuit is opened at the first moment that all the energy has been transferred to the secondary circuit, and no further beats or spark-gap losses occur.

Results were given showing that the oscillograph can be used to find the losses in condensers at various frequencies by discharging the condensers through inductances of known resistance.

Some Radio-telegraphic Apparatus in use at the City and Guilds College was briefly exhibited by Prof. G. W. O. HOWE.

The wireless telegraphic receiving apparatus was shown connected up to the aerial, which is 260 feet high.

A transformer specially designed for experimental work at long wave-lengths was shown. By means of a Brown telephone relay and special trumpets fitted to the telephone receiver, the time signals and messages sent out from Norddeich and from the Eiffel Tower can be plainly heard anywhere in the lecture theatre.

The various types of receiving apparatus in use at the College were shown.

Owing to lack of time the discussion on these two papers was omitted.

SOCIETY OF CHEMICAL INDUSTRY.
(LONDON SECTION).
Ordinary Meeting, April 3rd, 1911.

Mr. E. GRANT HOOPER in the Chair.

THE following papers were read and discussed :— "Measurement of High Temperatures." By C. T. HEYCOCK, F.R.S.

The author referred to the early pyrometer of Wedgwood, Deville and Troost's iodine thermometer, and other such appliances, and indicated their inherent errors. He also referred to the practical difficulties attending the use

i79

of the gas thermometer and of calorimetric pyrometers. He then referred to more modern methods, such as those dependent on (1) the alteration of resistance of a wire, (2) the alteration of the electro-motive force of a thermocouple, and (3) radiation methods.

The

Siemens appears to have been the first to use an electrical resistance pyrometer in 1871. Callendar reinvestigated this method of pyrometry, and constructed improved apparatus with compensating leads. accuracy of his formula connecting the alteration of resistance with temperature has recently been demonstrated by the use of the air thermometer up to a temperature near the melting-point of platinum.

The use of thermo-junctions of platinum, platinumrhodium; copper, constantan; or iron, constantan, was referred to as giving a rapid determination of temperature accurate enough for most purposes. Certain difficulties attending their use were alluded to.

Radiation pyrometers which may be used outside the furnace, of which Féry's is the best known, were then described. This is now largely used for measuring the temperature of baths of molten steel.

Greenwood's determinations of the approximate boiling. points of metals, such as antimony, bismuth, chromium, and copper, by an optical method, were mentioned.

'Gum from Bombax malabaricum." By P. P. PHILLIPS.

The Bombax malabaricum (vernacular name, semul), the red silk-cotton tree, is a large tree belonging to the Ñ. O. Malvacea, and is found in the plains of India and the subHimalayan tract up to a height of 3500 feet, and in other parts of Asia and in North Australia.

It yields a gum which exudes only from the portions of the bark which have been injured by decay or by insects. This gum is a white opaque viscous mass, which readily turns red, and finally dries into hard brittle mahoganycoloured tears. It is known in the vernacular as mocherus, and from its astringent properties is largely used in India as a medicine. The gum contains about 8 to 9 per cent of mineral matter, chiefly sand.

Various qualitative reactions are described which show that the gum contains a considerable quantity of tannin. It yields red substances on hydrolysis with dilute acid, one of which, "semul red," possesses the colour of crimson lake. The investigation is being continued.

RÖNTGEN SOCIETY.

The Effects of Secondary X-Ray Radiation. EVER since Prof. J. J. Thomson delivered the Address before the last meeting of the British Medical Association, in which he urged upon medical radiologists the value of the secondary homogeneous radiation proceeding from metals placed in the primary beam of the X-ray tube, a number of physicists on the one hand, and medical men on the other, have been devoting themselves to this problem. The pioneer in these investigations is Prof. C. G. Barkla, of King's College, London, and therefore more than an ordinary degree of interest attached to his Address on this subject before the Röntgen Society at its meeting on April 6th. After pointing out the value of the very soft or easily absorbed radiations obtained in this mannerradiations which have little influence in the primary beam from the tube when directed upon the tissues, because they are absorbed in the glass on their way out-he drew a distinction between the secondary radiation and the residue obtained after passing the beam through a filter. In the case of filtration there were non-homogeneous primary rays as well as homogeneous secondary ones. obtain the pure secondary radiation one must use the radiation proceeding from the surface of incidence-i.e., the metal plate or other substance-and that alone. There were three kinds of secondary radiation, he continued. The first was the scattered radiation proceeding from air

Το

CHEMICAL NEWS, April 21, 1911

THE CHEMICAL NEWS.

VOL. CIII., No. 2682.

A PHYSICO-CHEMICAL STUDY OF MERCURY
SODIUM ALLOYS OR SODIUM AMALGAMS.*
By ERNEST VANSTONE (B.Sc., Wales), 1851 Exhibition Research
Scholar, University College of South Wales and Monmouthshire.

NUMEROUS investigations on sodium amalgams have already been carried out, and the literature on this subject has become very extensive. The greater part of this refers to dilute liquid amalgams containing small quantities of sodium. Comparatively little work has been done on the solid amalgams. An excellent résumé of the work up to 1904 is given in Abegg's "Handbuch der Anorganischen Chemie," vol. ii.

From all the investigations the conclusion is drawn that several compounds of sodium and mercury exist. The number and composition of these compounds, however, are not known with certainty. Below is given a list of the formulæ suggested by various investigators.

The need of further investigation is obvious. It is well known that the ordinary valencies of the metals are not exercised in metallic compounds, and no satisfactory explanation of the nature of the union has been put forward. It was thought that an investigation of the specific volumes might throw light on this problem.

A dissertation has recently appeared by Bornemann ("Metallurgie," 1909), in which it is stated that the only methods for fixing with certainty the composition of these metallic compounds are those commonly employed by metallographers, namely :—

1. The investigation of the thermal diagram.

181

Schüller cut up the sodium under anhydrous ether and

transferred it to a weighed crucible containing vaseline

oil. Mercury was then added to the molten sodium.

In the present work the sodium was melted in a current of dry carbon dioxide, and caused to flow into a tube which had been previously weighed, and which was also full of carbon dioxide. The apparatus is shown in Fig. 1. A stick of sodium was placed in A, and the tube heated with a Bunsen burner until the sodium melted; on slightly diminishing the pressure in в the clean metal entered, leaving a shell of oxide in A. When cool, B was quickly stoppered and weighed. The stopper was then replaced by another of rubber, trebly bored. Through the wide central hole a glass tube, closed at its lower end, was passed.

This tube contained the thermometer, and also served as a stirrer, the rubber stopper allowing sufficient freedom of movement.

This mode of stirring was found necessary, owing to the fact that the amalgams adhere to glass and render it opaque. Through the other holes inlet and exit tubes for

points.

3. The preparation and examination of micrographs.

All three methods have been employed in the present work.

The Investigation of the Thermal Diagram. Preparation of the Alloys.-The method of preparing sodium amalgams commonly employed, namely, by plunging pieces of sodium under mercury, is unsuitable and

unnecessary.

Kurnakow melted sodium in a weighed retort, through which a stream of dry hydrogen was passing. A sufficient quantity of sodium was then poured off into an iron cylinder containing a little molten paraffin, and the retort was again weighed. The requisite quantities of mercury were then added to the sodium.

* A Paper read before the Faraday Society, March 14, 1911.

with a stopcock, the latter also serving for the introduction of mercury.

This was added from a small burette, which was weighed before and after. In preparing amalgams in this manner the sodium must be fused and the mercury added at first in small quantities; later, it may be added in large quantities, provided the alloy is kept molten.

(For ordinary purposes amalgams of all concentrations can be prepared as follows:-The badly oxidised surfaces of a piece of sodium are removed, and the sodium then dropped into ether containing traces of alcohol; ordinary methylated ether diluted with a large quantity of light petroleum answers very well.

In a few minutes the in molten paraffin contained in a crucible or test-tube, sodium becomes quite bright; it is removed and immersed heated to 100° C., and the requisite quantity of mercury then added).

Determination of the Freezing points. It will be shown later that the freezing points extend over a very wide range of temperature, namely, from -47° C. to +360° C.

The heating arrangement for temperatures up to 250° C. consisted of a very large boiling-tube filled with olive oil, provided with a stirrer, and illuminated from behind by means of an incandescent burner. For temperatures between 250° C. and 360° C. the tube was heated in a bath of fusible alloy.

For temperatures below o° C. the tube was placed in a boiling-tube containing light petroleum, and the latter cooled in a vacuum vessel containing a mixture of solid

Na her 100.

100

མ

carbon dioxide and alcohol. The alloy was heated until entirely liquid, then allowed to cool slowly, meanwhile being vigorously stirred. The temperature was read every minute or half minute. In nearly all cases superfusion was observed, and the points determined are the maximum temperatures reached after over-cooling. The thermometers used were mall Anschütz normal thermometers, each having a range of 50° C. and graduated in fifths.

Temperatures below o° C. were determined with a pentane thermometer graduated in degrees. These thermometers were previously standardised. Corrections for the exposed stem were obviated as far as possible, as these