53 



smaller steps. As soon as two phases are present, the equilibrinra 

 beoomes extremeir sensitive to the smallest change in pressnre or 

 temperatnre, and therefore the qnantities that determine the condi- 

 tions of equilibrinin must lie ke|>( as constant as possible, in the 

 critical zone, an alteration of a hnndredlh of a degree in the tempe- 

 rature will cause tiie mercury in the stem of the piezometer to rise 

 or fall by millimeters. Althuugh the e/ic/-poiiits of condensation could 

 be fairly accurately observed, provided the pressure-increases were 

 made with extreme care the tendency of the liquid phase to remain 

 out, despite vigorous stirring, did not allow of accurate observation 



J.ZJ 



J. o o 



C.7J 



o.oo 



aoc2.o 



Fig. 2. 



of the beginning-\iOmi. Both |ioiiits were accordingly graphically 

 taken from the isotherms by linding the intersection of the one- 

 phase and two-phase portions of the latter. Even in this way only 

 very approximate results can be obtained in the critical zone. 



The critical phenomena were well observed, both as regards the 

 typical opalescence at and near the plail-point, and the process o^ 



