It appears from the experiments of Brunner and of Wolf on the ascent of water in tubes that at the temperature t° centigrade
| T | = 75.20 (1 − 0.00187 t) (Brunner); |
| = 76.08 (1 − 0.002 t + 0.00000415 t²), for a tube .02346 cm. diameter (Wolf); | |
| = 77.34 (1 − 0.00181 t), for a tube .03098 cm. diameter (Wolf). |
Lord Kelvin has applied the principles of Thermodynamics to determine the thermal effects of increasing or diminishing the area of the free surface of a liquid, and has shown that in order to keep the temperature constant while the area of the surface increases by unity, an amount of heat must be supplied to the liquid which is dynamically equivalent to the product of the absolute temperature into the decrement of the surface-tension per degree of temperature. We may call this the latent heat of surface-extension.
It appears from the experiments of C. Brunner and C.J.E. Wolf that at ordinary temperatures the latent heat of extension of the surface of water is dynamically equivalent to about half the mechanical work done in producing the surface-extension.
References.—Further information on some of the matters discussed above will be found in Lord Rayleigh’s Collected Scientific Papers (1901). In its full extension the subject of capillarity is very wide. Reference may be made to A.W. Reinold and Sir A.W. Rücker (Phil. Trans. 1886, p. 627); Sir W. Ramsay and J. Shields (Zeitschr. physik. Chem. 1893, 12, p. 433); and on the theoretical side, see papers by Josiah Willard Gibbs; R. Eötvös (Wied. Ann., 1886, 27, p. 452); J.D. Van der Waals, G. Bakker and other writers of the Dutch school.
(J. C. M.; R.)
[1] In this revision of James Clerk Maxwell’s classical article in the ninth edition of the Encyclopaedia Britannica, additions are marked by square brackets.
[2] See Enrico Betti, Teoria della Capillarità: Nuovo Cimento (1867); a memoir by M. Stahl, “Ueber einige Punckte in der Theorie der Capillarerscheinungen,” Pogg. Ann. cxxxix. p. 239 (1870); and J.D. Van der Waal’s Over de Continuiteit van den Gasen Vloeistoftoestand. A good account of the subject from a mathematical point of view will be found in James Challis’s “Report on the Theory of Capillary Attraction,” Brit. Ass. Report, iv. p. 235 (1834).
[3] Nouvelle théorie de l’action capillaire (1831).