ments.

The scope of the new Committee is more extended than that of the old Committee. The discovery of Isotopy first in the domain of radioactive Elements, later in that of non-radioactive Elements, produced new problems not only concerning Atomic Weights, but also affecting the conception of a chemical Element.

In consequence, the International Union has decided that it should be the duty of the new Committee to keep chemists informed of the various advances made each year in this field already rich and so full of promise for the future.

The Committee will therefore prepare three tables: one Table of radioactive Elements containing their principal constants; one Table of Isotopes; one Table of Atomic Weights.

The International Union has decided that the Committee should consist of at the most 12 members, and it has itself elected 7 of these: MM. Aston (Great Britain), Brauner (Czecho-Slovakia), Debierne (France), Ph. A. Guye (Switzerland), Richards (United States of America), Soddy (Great Britain), Urbain (France).

It has appointed as experts for the year 1922 MM. Baxter (United States of America) and Moles (Spain). MM. Clarke and Thorpe are honorary presidents.

The Committee, to complete itself, has, in consequence of the regrettable death of Ph. A. Guye, elected MM. Baxter (United States of America) and Leduc (France). In accordance with its statutes the Committee has invited all the national branches of the International Union to create in their countries national Committees from which it may receive notice on any question connected with its activities.

Three of these national Committees are actually working, in Spain, France and Switzerland.

WORK OF THE COMMITTEE DURING THE
YEAR 1921-1922.

The Committee has prepared the two tables, of which the need was particularly felt a Table of radioactive Elements, and a Table of Isotopes.

The work of the Committee is not complete as regards the Table of Atomic Weights, which will be published later on. As a result the Table for 1922 drawn up by the old International Committee for Atomic Weights is accepted for 1923. It is on this account that the values which appear in the Table of Isotopes under the

title Atomic Weights are these given in the International Table for 1922.

In the case of the radioactive Elements the figures appearing under the title Atomic Mass are the values, rounded to the nearest whole number, from the Atomic Weights of Uranium (Uranium I), Thorium and Radon (Radium Emanation).

The Committee has found it necessary to modify the nomenclature of several radioactive Elements.

Each of the Tables is accompanied by notes which explain the signs, symbols and new names adopted by the Committee.

The Committee consider that, as regards the radioactive Elements and Isotopes, its work is only provisional. It recognised that the definitions and nomenclatures which have been adopted do not form a homogeneous whole. Until a general reform of the nomenclature of the radioactive Elements is under consideration it has respected as far as possible the names given by the discoverers. On this account, before adopting for the three emanations the names Radon, Actinon and Thoron, the approval of Mme. Curie and Sir E. Rutherford was obtained.

The Committee hopes that the new International Tables will be favourably received by the scientific world, and that the values adopted will be generally approved.

F. W. ASTON.

GREGORY P. BAXTER. BOHUSLAV BRAUNER. A. DEBIERNE.

A. LEDUC.

T. W. RICHARDS. FREDERICK SODDY. G. URBAIN.

INTERNATIONAL TABLE OF ISOTOPES (1923). Atomic Number.-A chemical element is defined by its atomic number. This number represents the excess of positive over negative charges in the constitution of the atomic nucleus; theoretically the atomic number represents also the number of eleetrons which rotate round the central positive nucleus of the atom. Each atomic number also represents the place occupied by the element in the Mendeléef Table.

Various methods have been suggested to determine the atomic numbers. The most important of these consists in deducing them from the wave-lengths of the high frequency spectra by applying Moseley's law.

feeble.

1 The expression "atomic mass' is re served for isotopes or simple elements considered from the isotopic point of view The expression ATOMIC WEIGHT retains its

usual meaning, and is applied to elements without consideration of their isotopic constitution.

CATALYST POISONING.

At the Chemical Society of the University of Birmingham, on February 19-Professor Morgan presiding-Dr. Edward B. Maxted, chairman of the Birmingham and Midland Section of the Society of Chemical Industry, read a paper on "Catalyst Poisoning.

Poisoning may be specific rather than general, the author pointed out, for what is a poison for a given reaction with a given catalyst may be harmless for a second reaction with even the same catalyst or even for the same reaction with a different catalyst.

The following is a summary of Dr. Maxted's remarks:

1. Catalyst poisoning consists of the preferential adsorption of the poison by the catalyst, in such a way that the secondary valencies of the catalyst, in place of being free for transitory association with the normal reacting system-the probable mechanism of ordinary catalysis-are obstructively saturated by the poison. By obstructively saturated is meant that the free evaporation of the adsorbed poison from the surface of the catalyst and its replacement by the normal reacting system does not take place or, at all events, not readily.

2. From the above, it follows that if a given inhibitant poisons a given catalyst, then the catalyst will adsorb the poison. The adsorption of a poison by a preliminary charge of catalyst may in some

some in

stances be used to purify a reacting system; but in most cases the amount actually removed by a given weight of catalyst is too small for the method to be used practically.

3. The activity of a catalyst during the first stages of poisoning is a linear function of the poison content, and the form of the poisoning curve is intimately connected with that of the adsorption curve.

4. The general type of the reaction curve is not affected by the presence or absence of a poison insufficient in quantity or the complete suppression of activity, provided that the concentration of the poison on the surface of the catalyst does not change during the reaction, and provided also that the form of the catalyst does not change.

action have been studied, and whereas both acetone and acetic acid act as diluents, not actually decreasing the dehydrating power of sulphuric acid, if the volume of acetic acid is great, i.e., 1 vol. H2SO1 to 10 vols. CH,COOH, the formic acid is not decomposed. On the other hand, hydrogen chloride increases the velocity of the reaction. Again, copper, silver, and other sulphates decrease slightly the velocity of reaction. (Jour. Amer. Chem. Soc., 1923, p. 447.)

Temperature on some of the Properties of Steel.

In this paper experiments are described in which the period of torsional vibration and the length of a steel wire were automatically and continuously recorded in terms of time, while the temperature was varied between 15° and 1,000° C., the temperature also being recorded.

From the experiment the variation of rigidity and the coefficient of temperature expansion between these limits can be deduced.

The results show (1) that the variation of the rigidity of steel between ordinary temperature and a dull red heat is smal. (less than 1 per cent.); (2) that above the critical temperature (about 800° C.) the rigidity decreases rapidly; (3) that the temperature coefficient of expansion does not show any marked change as the metal passes through the critical temperature: but (4) that a comparison with the cooling curves of iron and steel (alluded to in the paper) proves that the specific heat of the high temperature form of the metal is much less than it is at temperatures below the critical point.

PROF. C. H. LEES, F.R.S. Inductively Coupled Low-Resistance Circuits.

It is shown that the oscillations in each of two circuits of low resistance coupled by their mutual inductance can be simply expressed in terms of a certain product of capacitance and inductance. The expres sions for the currents lead to a simple graphical solution of the problem.

LORD RAYLEIGH. F.R.S. Studies of Iridescent Colour, and the Structure producing it. I. The Colours of Potassium Chlorate Crystals.

The structure of the iridescent potassium chlorate crystals investigated by Stokes and the late Lord Rayleigh is examined microscopically.

The periodic twinned structure inferred by the latter is clearly shown in the photographs taken under the microscope with polarised light.

Some crystals have exceedingly complex structure, showing many groups of evenly spaced twin planes and a very complex reflection spectrum. It is shown that this results from high interference from twinned layers situated a considerable distance apart.

Chlorate crystals, giving a silvery reflection, were obtained by Madan, who heated the ordinary colourless crystals to about