Abstract
IN a recent very interesting communication to the Birmingham Phil. Soc. (Bir. Phil. Soc. Proc., vol. ix. part 1, 1893), upon the effect of a solid in concentrating a substance out of a solution into the superficial film in accordance with Prof. J. J. Thomson's investigation (“Applications of Dynamics to Physics,” p. 191), Dr. Gore has quoted an observation of Pouillet's (Annales de Chemie, 1822, vol. xx. pp. 141–162), that when inert powders like silica are mixed with liquids that do not act on them heat is evolved. On the other hand, when the superficial area of contact between a liquid and its gas is increased heat is absorbed. This latter is known to be the case because the superficial tension diminishes with rise of temperature. In the case of the solid-liquid surface being produced, it would appear at first sight to follow that the superficial tension should increase with increased temperature. The matter is, however, somewhat more complicated. When a dry solid is mixed with a liquid we are substituting a solid-liquid surface for a solid-air surface, and from the fact that most liquids soak up into a mass of dry powder, we may conclude that the superficial potential energy of the solid-liquid is less than that of the solid-air surface, i.e. that more work must be done to separate the liquid from the solid than is developed by the air getting at the solid. If these actions are reversible, we may apply the laws of thermodynamics, and conclude that as heat is evolved when the system does work, i.e. when the solid-liquid surface is increased, that it must require more work to separate the solid from the liquid at high temperatures than at low ones, and in the case of silica and water, for instance, that is very much what one would expect from the action of water at very high temperatures on silica. If we could assume that the superficial tension of air-solid were zero, it would follow from this that the superficial tension of a solid-liquid surface is negative, i.e. that there is a superficial pressure, and that the liquid has more attraction for the solid than for its own particles, and that this difference increases with increased temperature, i.e. the superficial pressure increases.
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FITZGERALD, G. On the Change of Superficial Tension of Solid-Liquid Surfaces with Temperature. Nature 49, 293 (1894). https://doi.org/10.1038/049293a0
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DOI: https://doi.org/10.1038/049293a0
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