( 294 ) 



With the aifl of these coefficients of pressure the unstable parts 

 of the isothermal lines were extrapolated and mapped on the figure. 

 Only for 15°. 30 and 21°. 50 the extrapolated parts deviate suffi- 

 ciently' from those observed, to Ije clearly distinguished. As in 

 the case of a |)ure substance the two curves intersect and the areas 

 thus included must be equal as in the case of a pure substance ^). 

 Wc can immediately see on the figure that this condition is satisfied, 

 in so far as we can judge by examination only. A more accurate 

 test by measuring the areas is useless on account of the uncertainty 

 of the extrapolation we have made. 



§ 4. The course of the condensation. 



Below the temperature of the plaitpoint the process of the conden- 

 sation was normal : the quantity of fluid was constantly increasing 

 while the volume was decreasing, so that finally the whole space 

 was filled with liquid. Between the temperature of the critical point 

 of contact and the plaitpoint-temperature retrograde condensation was 

 distinctly observed. 



In order that we might represent the process of the condensation 

 graphically, I measured volumes of liquid belonging to definite volumes. 

 The results of these measurements are given in Table II. 



This table is graphically represented in fig. 2. There we can dis- 

 tinctly see the normal course of the condensation below the plaitpoint- 

 temperature 27.°1Ü; the lines of condensation are constantly rising 

 and end in points lying on a straight line with a slope of 45°: at 

 these points the volume of the liquid is equal to the total volume. 

 Above the plaitpoint-temperature the condensation-line rises first 

 but finally returns with great rapidity to the axis of abscissa ; the 

 course of these condensation-lines is therefore very asymmetrical, and 

 even more so the closer we get to the plaitpoint; in approacliing 



') See Blümckk, Zeitscbr. f. physik. Ghem., VI, p. 137. 



