Aug., 1924.l MOLECULAR ATTRACTION. I59

sense in which it has been generally employed, but refers to group movements.) The subsequent ionization of this complex-

CH,, CH,, + - CH,, O.HBr---+ CH,, OHfBr

is in favo; of this point of view.

CONCLIlSION.

To sum up : The experimental determination of physical prop- erties may be used to give an insight into the relative magnitude of molecular attractions existing between molecules when the orientation is taken into account. The molecular attraction between diverse species can be measured by gas mixtures, and if the attraction is strong enough molecular complexes result which can also be investigated by freezing-point curves; molecular attraction plays a part in governing the velocity of a chemical reaction. Rise in temperature increases the vibration of the atoms in the molecule which accelerates chemical reaction, but it seems plausible that in certain types of reaction orientation between molecules is necessary. ,4s this can take place more readily if the molecules are moving slowly, reaction occurs between that very small number of molecules which, according to Maxwell’s distribution law, have small translatory velocity and at the same time high vibratory energy of the atoms. This governs the tem- perature coefficient of the velocity of a chemical reaction.

The experimental work carried out so far is but the beginning, and as more data are accumulated some of the ideas put forward may prove to be wrong. However, they have been the incentive for undertaking these particular researches, and even if they do prove to be wrong, that will not take away from the pleasure which was derived from the carrying out of the experimental work, which has presented numerous difficulties.

On the X-ray Corpuscular Emission from Iron in a Magne- tized and Unrnagnetized State. G. A. CARSE. (Proc. Roy. Sot. Edin., Vol. 53, Part III.)-In an endeavor to ascertain the ultimate cause of magnetism a number of experiments have already been made to compare the effects produced by magnetized and unmagnetized substances. Forman investigated the relative absorption of X-rays and “ found that the absorption coefficient of iron for X-rays did not alter when the iron was magnetized in a direction perpendicular

160 CURRENT 'I‘OPICS. [J. F. I.

to the beam, and that a small increase in the coefficient, amounting to five parts in a thousand for a field of 3500 gauss, was observed when the iron was magnetized parallel to the beam.

“ Compton and Trousdale’s experimental results indicated that in no case did magnetization influence the diffraction pattern.

“ Compton and Rognley, as a result of their experiment, observed no change in the intensity of a beam of X-rays reflected from magne- tite when the crystal was magnetized.

“ Poole showed that when iron is magnetized there is apparently no large change in the total number of electrons emitted by the iron surface under the influence of ultra-violet light.”

In the experiment described in the present paper a cube of soft iron was mounted in an ionization chamber with one of its axes verti- cal. Two opposite vertical faces of the cube were covered with cop- per. X-rays fell normally on one of the uncovered iron faces and the resultant emission of electrons was measured by the ionization produced in hydrogen. A magnetic field at right angles’ to the direction of the beam and sufficiently strong to saturate the iron approximately was thrown into action and the ionization was again measured. To eliminate the effect of the field on the corpuscles after their emission the same pair of observations was made with the rays incident on a copper face. After all allowances had been made the author draws the conclusion, “ It would seem, as far as this experiment goes, that in the iron atom, either the part of the atom that turns does not emit an appreciable number of electrons, or the chance of ejection is not affected by the orientation.” G. F. S.

Note on Tuning Forks. C. C. MASON. (Jour. Scirutific Zrutr., May, Igz4.)-In the case of a fork rigidly supported. there are three simultaneously vibrating systems, the support, and the two prongs. The two prongs may vibrate with different frequencies. The author measured the frequencies of the prongs of a badly balanced fork and found them to be 48 and 50, respectively. This fork did not seem to be especially poor except that it died down rapidly when held in the hand and struck. Set in vibration in this way a well-balanced fork will vibrate a considerable time because it is damped only by the air and, to a small extent, by elastic hysteresis. “ It should he remem- bered that in a fork the two prongs vibrate in opposite phase, and it is only in the case of exact symmetry that the two bending moments at the base of the prongs are at every instant equal and opposite. It is not only necessary that each prong should have the same natural period, but the energy in each prong must be the same. When the two bending moments are not exactly equal, a bending moment equal to their difference is transmitted to the stem or handle of the fork.”

The Cambridge Instrument Company has made a fork of elinvar with a coefficient of frequency of only .0oooo47 per degree C. A steel fork has a coefficient about twenty times as large. Unfortunately the alloy is both expensive and hard to work. G. F. S.