A Source Book in Physics

Author: James Prescott Joule  | Date: 1862

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Free Expansion of Gases

A brief notice of some of the experiments contained in this paper has already appeared in the ’Proceedings.’ Their object was to ascertain with accuracy the lowering of temperature, in atmospheric air and other gases, which takes place on passing them through a porous plug from a state of high to one of low pressure. Various pressures were employed, with the result that the thermal effect is approximately proportional to the difference of pressure on the two sides of the plug. The experiments were also tried at various temperatures, ranging from 5° to 98° Cent.; and have shown that the thermal effect, if one of cooling, is approximately proportional to the inverse square of the absolute temperature. Thus, for example, the refrigeration at the freezing temperature is about twice that at 100° Cent. In the case of hydrogen, the reverse phenomenon of a rise of temperature on passing through the plug was observed, the rise being doubled in quantity when the temperature of the gas was raised to 100°. This result is conformable with the experiments of Regnault, who found that hydrogen, unlike other gases, has its elasticity increased more rapidly than in the inverse ratio of the volume. The Authors have also made numerous experiments with mixtures of gases, the remarkable result being that the thermal effect (cooling) of the compound gas is less than it would be if the gases after mixture retained in integrity the physical characters they possessed while in a pure state.


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Chicago: William Thomson et al., "Free Expansion of Gases," A Source Book in Physics in A Source Book in Physics, ed. William Frances Magie (Cambridge: Harvard University Press, 1935), 173–174. Original Sources, accessed March 24, 2023, http://www.originalsources.com/Document.aspx?DocID=LLBF97QJVPTDMR9.

MLA: Joule, James Prescott, et al. "Free Expansion of Gases." A Source Book in Physics, Vol. 12, in A Source Book in Physics, edited by William Frances Magie, Cambridge, Harvard University Press, 1935, pp. 173–174. Original Sources. 24 Mar. 2023. http://www.originalsources.com/Document.aspx?DocID=LLBF97QJVPTDMR9.

Harvard: Joule, JP et al., 'Free Expansion of Gases' in A Source Book in Physics. cited in 1935, A Source Book in Physics, ed. , Harvard University Press, Cambridge, pp.173–174. Original Sources, retrieved 24 March 2023, from http://www.originalsources.com/Document.aspx?DocID=LLBF97QJVPTDMR9.