Abstract
A VERY interesting paper by Prof. J. J. Thomson, on the effects of electrification and chemical action on a steam jet, and of water vapour on the discharge of electricity through gases, appears in the October number of the Philosophical Magazine. In it the author first considers the effect of an electrical field on the surface tension of a water drop, and he shows that if the electrical field is uniform, the diminution in the surface tension is very small and independent of the size of the drop; so that a uniform field will not be able to counterbalance the effect of surface tension, since the latter varies inversely as the radius of the drop, and therefore when the drop is excessively small must be greater than the constant effect due to the electric field. When, however, the electric field instead of being uniform is due to a number of charged atoms distributed throughout the volume occupied by the steam, the effect of the electric field in diminishing the surface tension varies inversely as the square of the radius of the drop. Thus for very small drops the electrification will overpower the cause (surface tension) which, under ordinary circumstances, puts an end to the existence of small drops. The above seems capable of explaining the effects of electrification on a steam jet first observed by Helmholtz, for the electricity which escapes into the gas is carried by charged atoms of the gas, and since in the region immediately around these atoms there will be a very intense electric field there will be a tendency for the steam to condense into drops in these regions. Helmholtz also discovered that chemical action in the neighbourhood of the jet affected it in much the same way as a discharge of electricity. If the forces which hold the atoms together in a molecule are electrical in their origin, so that in a diatomic molecule one atom has a positive and the other an equal negative charge, the above explanation will also apply to this case. For when the molecule of the gas is in the ordinary state, the equal and opposite charges of the atoms will, in the region outside the molecule, neutralise each other's effect, so that the electrical field round a molecule will be much less intense than that round a single charged atom, and thus, though the field round the latter may be sufficient to cause condensation, that round the molecule may not. When, however, the molecules which enter into chemical combination come together and form a new compound, requiring a rearrangement of the atoms, then while the chemical change is going on, there will be an interval during which the atoms are comparatively free, and there will be an electric field almost as strong as if the atom were dissociated.
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The Effect of Water Vapour on Electrical Discharges. Nature 48, 605–606 (1893). https://doi.org/10.1038/048605a0
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DOI: https://doi.org/10.1038/048605a0