The London, Edinburgh and Dublin philosophical magazine and journal of science . ebeing maintained constant), a point B is reached at which theliquid begins to boil, and the whole mass may be transformedinto the gaseous state under constant pressure, if heat besupplied to keep the temperature constant while the volumeis allowed to increase from B to D. The part BD of theisothermal is consequently a right line parallel to the axis ofvolume, and at D the whole mass is in the condition ofsaturated vapour. Beyond D the curve DE is approximatelya rectangular hyperbola as it represents the isotherma
The London, Edinburgh and Dublin philosophical magazine and journal of science . ebeing maintained constant), a point B is reached at which theliquid begins to boil, and the whole mass may be transformedinto the gaseous state under constant pressure, if heat besupplied to keep the temperature constant while the volumeis allowed to increase from B to D. The part BD of theisothermal is consequently a right line parallel to the axis ofvolume, and at D the whole mass is in the condition ofsaturated vapour. Beyond D the curve DE is approximatelya rectangular hyperbola as it represents the isothermal of agaseous substance which approximately obeys Boyles law. Very shortly after Andrews5 celebrated experiments on theisothermals of carbon dioxide, and on the continuous trans-formation of matter from the gaseous to the liquid state,Professor James Thomson, in an ingenious speculation (sug-gested by the shape of the isothermals immediately above thecritical temperature), proposed an isothermal curve of theform represented in fig. 2, which embraces the idea of conti- Fig. O V nuity of transformation, so much insisted on by , in passing from B to D, the substance is supposed tobe homogeneous throughout, and not to be partly liquid andpartly vapour as in the corresponding part BD of the iso-thermal of fig. 1. The word homogeneous must here, how-ever, be taken with some reservation, for although the mass,as a whole, may be apparently homogeneous—that is, onecubic centimetre may be on the whole the same as another,—yet when considered in very small portions the mass may beintensely heterogeneous. For example, small portions may Transformation from the Liquid to the Gaseous State. 233 approach the gaseous state more nearly than the liquid, whileothers may be more decidedly in the liquid condition*. Since the time of Andrews and Thomson, various attemptshave been made to deduce from dynamical principles a generalrelation connecting the volume, pressure, and tempe
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Keywords: ., bookcentury1800, bookdecade1840, bookidlondon, booksubjectscience
