Abstract
LONDON. Royal Society, March 8.—A. B. Wood, H. E. Browne, and C. Cochrane: Determination of velocity of explosion-waves in sea-water; variation of velocity with temperature. An accurate determination of the velocity of explosion-waves in the sea gives: (a) V= 4955.5 (±1) ft./sec., at 16.95 (±0.1)° C. and salinity 35 per cent. (b) V=4836 (± 2) ft./sec., at 6.0 (±0.1)° C. and salinity 35.1 per cent. (c) V= 4847 (±1.5) ft./sec., at 7.0 (±0.1)° C. and salinity 35.2 per cent. In the new technique developed, it is unnecessary to know the exact position of charge relative to receivers. The results lead to a mean value of 10.9 ft./sec. per ° C. as the temperature-coefficient of velocity in the range 6° C. to 17° C. The following expression represents the velocity at any temperature t° C. within this range, and at any salinity S (parts per thousand): V= 4627 + 13.7t – 0.12t2 + 3.73S. The salinity-coefficient is approximately 3 to 4 ft./sec. per 1 per cent. increase of salinity, the theoretical value being 3.73 ft./sec. per 1 per cent. No change was detected for charges varying in weight from 9 oz. to 300 lb. of explosive and no variation with depth. The coefficient of adiabatic compressibility of sea-water at 16.95° C. and 35 Per cent. is Crho;= 42.744 (±0.02) × 10–6. Combining this with Ekman's value of Cθ, the ratio of the specific heats of sea-water under these conditions of temperature and salinity γ=1.0094 ± 0.0005, in good agreement with 1.0090, deduced from thermo-dynamic data.— P. M. S. Blackett: The study of forked alpha-ray tracks. Forked alpha-ray tracks obtained by the Wilson condensation method were studied. The lengths of the tracks of the recoil atoms yield information concerning the relative ionisation"due to different kinds of ionising particles, and of the average charge carried by them. Measurements of the angles between different parts of the tracks gave the masses of the recoil atoms in three particularly favourable cases.—A. Egerton: On the vapour pressure of lead.—I. The vapour pressure is measured by effusion of vapour at low pressure through a hole of measured area. Temperature is maintained constant by a selenium cell relay arrangement within 1/3° C. for many hours at about 800° C. Pressures were measured to 10–5 mm. The vapour pressure of ordinary lead between 1200-600° absolute is expressed by the equation log p=7.908–9932/T. The latent heat of vaporisation of lead (λo) is 47,000 ± 1000 cal. The chemical constant of lead is 1.84 ± 0.2, agreeing well with the theoretical value (1.853) obtained from the relation 3/2 log M – Co=C. The vapour pressures of lead and the uranium-lead isotope appear to differ by 2 per cent., but the result is rendered uncertain by an unexplained lowering of vapour pressure which lead undergoes on prolonged heating in vacuo.—A. C. Egerton and W. B. Lee: (1) Some density determinations. The Archimedes method of determining densities is rendered more accurate by utilising certain mobile and heavy organic liquids which avoid air bubbles and damping difficulties, and increase the weight of liquid displaced. Ethylene dibromide and carbon tetrachloride were employed with accuracy. A satisfactory sample of metal for density determination is prepared by filtering, casting, and heating in vacuo. The density of lead is 11.3437 at 20° C. The probable error of the nine determinations on three different samples is 1 part in 100,000, The maximum departure from the mean value for any single determination is less than 1 part in 12,000. A sample of uranium-lead would have an atomic weight of 206.26 from the density obtained. (2) Separation of isotopes of zinc. Two sets of distillations of pure zinc have been carried out in high vacuum, under conditions to obtain a slightly different concentration of the isotopes in the final residue of the final distillate. The samples are cast in vacuo and seeded with a particular kind of zinc. The first distillations gave a residue of slightly increased density, but the distillate possessed the same density as the original zinc. The second distillations gave a residue of increased density (about 1 part in 3700) and a distillate of decreased density (about 1 part in 3000). Determinations on seven samples of ordinary zinc give the density of zinc (prepared in the described way) as 7.1400 (the probable error being less than 1 part in 100,000). Flaws, allotropes, different physical conditions, and impurities are improbable. The amount of the separation agrees with Dempster's observations of isotopes of weights extending over six units (namely, 64–70), but is not so great as might be found for equal parts of 64 and of atoms of weights 66, 68, and 70.—E. Hatschek and P. C. L. Thorne: Metal sols in non-dissociating liquids. I.—Nickel in toluene and benzene. Very stable sols of nickel in a medium free from ions can be produced by decomposing nickel carbonyl dissolved in mixtures of toluene and benzene, containing a small amount of rubber, at 100° C. In the electric field the particles of disperse phase move to, and deposit on, both electrodes. Electrophoresis in fields of different strengths, all other factors being equal, shows that the amounts deposited are proportional to the first, or a lower, power of the potential gradient. Therefore positively and negatively charged particles are originally present in the sol. The sol resembles typical protected aqueous sols, inasmuch as it is coagulated by liquids which are not solvents for the protective colloid, i.e. rubber. The coagulum is only very imperfectly peptised again by rubber solvents, such as toluene or benzene.—H. Hirata: Constitution of the X-ray spectra belonging to the L series of the elements.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies. Nature 111, 381–383 (1923). https://doi.org/10.1038/111381a0
Issue Date:
DOI: https://doi.org/10.1038/111381a0