Abstract
LONDON. Royal Society, February 19.—O. W. Richardson and A. F. A. Young: The thermionic work-functions and photoelectric thresholds of the alkali metals. The photoelectric threshold for normal potassium is close to 7000 A.U., which agrees with the known wavelength of maximum activity Amax and the equation A0 = f Amax. Uncertain traces of a thermionic threshold agreeing with this have been found at about 200° C. in one experiment, but the thermionic thresholds usually effective at this and lower temperatures are of a much lower magnitude, even under the best vacuum conditions. A common thermionic threshold effective at about 200° C. corresponds to X0 = about 10,000 A.U. A photoelectric emission with this infrared threshold has been got by exposing potassium to a luminous discharge in hydrogen or water vapour. This may be due to the growth of small patches normally present. There is no evidence of photoelectric activity further out in the infra-red, although there is a thermionic threshold which corresponds to AO = 30,000 A.U. The glow discharge not only brings out undeveloped thresholds, but it also augments the normal emission.-J. H. Brinkworth: On the measurement of the ratio of the specific heats using small volumes of gas. The quantity actually measured is the cooling effect in adiabatic expansion, i.e. the ratio of the drop in temperature to the drop in pressure. These two quantities are measured directly, the former by using a suitable platinum thermometer, and the latter from the readings on an oil gauge. THe values of the ratio of the specific heats thus experimentally obtained are used for the calculation of the specific heats of air and of hydrogen. The specific heat of air at constant pressure is practically constant, and equal to 0-2395 cal./gm. ° C. over the temperature range 155° to 290° A. The molecular heat of hydrogen falls rapidly from 4-88 at 290° A. to 3 -30 at 90° A. None of the theoretical curves representing the variation in the molecular heat of hydrogen agrees with the experimental curve, the divergence, at some temperatures, being certainly five times greater than an outside estimate of the inaccuracy of the experimental results.-F. H. Constable: The catalytic action of copper. Part VI. Chemical reaction occurs only when an alcohol molecule is adsorbed over a characteristic arrangement of copper atoms, called a reaction centre. There is a large variation in the number of atom centres lying beneath one adsorbed alcohol molecule on various Crystal faces: thus the reaction centre density varies also. The activity of the surface is controlled by the exponential activation factor, and by the reaction centre density on the surface.-Part VII. The rate of dehydrogenation of ethyl and butyl alcohols has been studied at pressures from 10 cm. of mercury to two atmospheres. The reaction velocity was found to be independent of the pressure.-V. H. Stott, Edith Irvine, and D. Turner: Viscosity measurements with glass. For the range io6 to io17 poises, the apparatus is a modification of the method of Trouton and Andrews, in which the resistance to torsion of a circular rod is determined. This apparatus may be readily modified so as to extend its applicability down to io4 poises. Measurements of lower viscosities down to about io2 poises depend on determinations of the rate of fall through the glass of a partially counterpoised iridio-platinum ball. Temperature uniformity in the latter case has been achieved by the use of an electrically heated "black body "furnace possessing novel features.-W. G. Palmer and F. H. Constable: The catalytic action of copper, Part V. The reaction velocity-temperature curves for ethyl, M-propyl, butyl, isobutyl and isoamyl alcohols (which have in common the grouping - CH2OH) are identical within the limits of experimental error. This identity involves also the equality of the temperature coefficients and of the heats of activation. The higher alcohols caused rapid "poisoning "of the catalyst, but this secondary effect was circumvented.—P. A. M. Dirac: The adiabatic invariance of the quantum integrals. The postulate of the existence of stationary states in multiply periodic dynamical systems requires that if the condition of such a system, when quantised, is changed in any way by the application of an external field, or by the alteration of one of the internal constraints, the new state of the system must also be correctly quantised. It follows that the laws of classical mechanics cannot in general be true, even approximately, during the transition. During the so-called adiabatic change, which takes place infinitely slowly and regularly, so that the system practically remains multiply periodic all the time, classical laws may be expected to hold. In this case the quantum numbers cannot change, and it has been possible to deduce from the classical laws that the quantum integrals remain invariant.-D. !L. Watson: The thermal decomposition of derivatives of oxalacetic ester: a unimolecular reaction. The decomposition, on heating, of derivatives of oxalacetic ester into a malonic ester derivative and carbon monoxide obeys the unimolecular (or simple probability) law, dx/dt = k (a - x), and the velocity is uninfluenced by diluting with solvents or adding acidic substances, though retarded by high concentration of carbon monoxide. None of the substances could be stimulated to react by light of wave-length predicted from the Lewis-Perrin theory, or by ultra-violet radiation, which they absorb very strongly. They had energies of activation between 33,000 and 36,000 calories, and an "active life "of the order of io˜14 second, in agreement with many other first-order changes. The velocity of decomposition of phenyl-oxalacetic ester, however, was proportional to the amount of phenyl-malonic ester formed by the change (exceptwhen the latter substance was present in excess). This law, characteristic of simple reactions in pure liquids, may be explained by the hypothesis of "reflex- activation,"namely, that highly energised products of reaction are largely responsible for formation of fresh "active "molecules. Here, as in all known unimolecular reactions, two species of molecules evidently take part in the change. -K. R. Rao: (i) On the fluorescence and channelled absorption of bismuth at high temperatures. The absorption spectrum has been photographed at temperatures of the order of 1500° C. Some of the absorption bands in the visible region exhibit distinctly a fine structure, showing that these are due to the triple quantification. The vapour emitted a fluorescent radiation, and the fluorescent banded spectrum ranging from \657o-X504o, containing about 20 bands, shaded towards the red, has been photographed. This banded fluorescent spectrum indicates probably that the critical potentials of elements which are polyatomic are related to the molecule and not to the atom.-(2) A note on the absorption of the green line of thallium vapour. The green line of thallium consists of an intense central doublet accompanied by two satellites. Absorption by a column of non-luminous vapour indicates complete absorption of the central doublet at about 800° C., at which temperature the satellite was but very feebly absorbed. The total absorption of the satellite took place at about 950° C.-B. F. J. Schonland: The passage of cathode rays through matter. Cathode rays of velocities up to 0-55 that of light (100,000 volts) in quantities easily measurable on a galvanometer, were produced. These rays have been used to extend measurements of cathode-ray absorption to the /3-ray region. The difference in variation of apparent absorption with velocity for different elements depends upon the fact that this is not a true absorption, since it includes the effect of the scattering back of rays on the side of incidence. The existence of a range for these rays has been established, and the values found for ranges at various velocities in aluminium are in close agreement with those calculated on Bohr's theory of absorption, which has now been tested from with rays of penetrating power varying in the ratio of i to 5000. Cathode-ray absorption is due to gradual loss of energy of moving particles by collisions with electrons in matter. An examination of the principles underlying Bohr's theory of absorption shows that interchange of energy in such collisions must take place more freely than the usual conceptions of atomic structure allow. Absorption of cathode rays of various speeds by atoms of a given element does not appear to show any discontinuities corresponding to those observed in X-ray spectra.
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Societies and Academies. Nature 115, 321–323 (1925). https://doi.org/10.1038/115321b0
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DOI: https://doi.org/10.1038/115321b0