( 147 ) 



we substitute iu it flie expression for h which we get by solving 

 the equation which e\|)resses tiie variability of h witii v and T — 

 the possibility of a dependency of h on T being admitted. We shall 

 represent the solution of this equation by 



I hit the general course has remained the same; e.g. the fact that 

 for tem[)eratnres below the critical temperature a maximum and a 

 minimum pressure occurs. The critical temperature is that for which 

 this maximum and this minimum pressure coincide and the critical 

 point may again be calculated from the three equations: 



2> = F(r, 7'), 



dvjT 



ydv'jT 



If therefore we could exclude all disturbing influences, if we 

 could neglect phenomena of capillarity aiid adsorption, if we could 

 neutralize gravity, if we could keep the temperature absolutely 

 constant throughout the space occupied by the substance, if we 

 could perform the experiments with perfectly pure substances without 

 the slightest trace of admixtures and if w^e could suppose that the equi- 

 librium is established instantaneously, then we should have coexistence 

 of two homogeneous phases of well defined proj)erties for all tempera- 

 tures below the critical one, and exactly at the critical temperature 

 only one homogeneous phase of well defined properties would exist. 



But the requirements enumerated here can never be fulfdled. 

 Already below the critical temperature deviations occur. The straight 

 line representing the evaporation parallel with the v-axis has probably 

 never been realised as yet in connection Avith the circumstance 

 that nobody has as yet experimented with a perfectly pure substance. 

 The boiling point always varies when the distillation is continued, 

 chiefly if we observe near the critical temperature. If in a closed 

 vessel we heat a substance which is separated into a liquid and a 

 vapour phase, then the pro])erties of the liquid phase may be varied 

 by shaking the vessel (Evershkim. Phys. Zeitschr. lö»^'» June 1903), 

 probably in connection with the circumstance that the liquid expanding 

 during the heating is internally cooled in consequence of the expansion 

 and the evaporation and reaches the surroundijig temperature only 

 very slowly by conduction; and also in connection with the always 

 occurring impurities. If further the substance is sulijected to gravity, 

 then neither vapour phase nor liquid phase is homogeneous. To 



