{ 234 ) 



pressures p and determine each time tlie composition of those two 

 quantities either by chemical or by physical means. 



voup. 



Fig. 1. 



Fig. 2. 



On the V .r-projection of the binodal curve of the transverse plait 

 on VAN DPiR Waals' if'j;?;-surface for a given temperature T, fig. 1, 

 and also on the p x diagram of that binodal line, fig. 2, two such 

 phases are indicated by a and b, for instance. The determination 

 of several pairs of values n h, a h' etc. gives then the whole course 

 of p, X and v over the transverse plait for T. 



If we follow the second method we obser\ e in a series of mix- 

 tures with a known composition x, the beginning- and endcondensation 

 phase and determine for them p and /", hence /y/.y and pcxT, ^^^^^ 

 vixT, ^n^l ^oxT' This investigation comprises each time the phases 

 represented in fig. 1 and 2 by b and c. By combining the results 

 b c, b' c' etc. we can derive again the binodal line and hence the 

 values for 'xi^/r, x^^/r, rij/r and Va,>T- The application of this last 

 method to low temperatures especially under moderate pressures, 

 forms the subject of this paper. 



It is possible to follow also the first method in the case of low 

 tem|)cratures as it has been applied by Hartman in Comm. N". 43 

 (June '98) for ordinary temperatures. Yet as a rule the analysis of 

 a gaseous mixture is much more difficult than the preparation of a 

 mixture of a definite composition (among others, by means of the 

 mixing apparatus of Comm. N". 84, Dec. '02) and it is difficult to 

 obtain certainty whether the quantities of vapour and liquid run off 

 have the same composition as • the phases which are brought to 

 equilibrium by stirring. 



Therefore it is important to solve the difficulty which accompanies 



