( 660 ) 
for the pure substance from the observed plaitpoint phenomena 
Tyls Ppl and vp), in a substance with small impurities (in a mole- 
cular proportion «). These constants were thought by KAMERLINGH 
OnnuS especially suitable to determine the phenomena in the case 
of small admixtures. It is also desirable to represent the differences 
in composition of the co-existing phases, the variations in pressure 
at the condensation of a mixture and the further deviations in 
properties of such a mixture from the pure (normal) substance by 
means of the same constants and the reduced quantities of a simple 
(normal) substance. For in this way we can avail ourselves of the 
empirically reduced equation of state for simple (normal) substances 
and of the empirical relations connected with it for the application 
of VAN DER WAALS’ theory to the calculation of the relation between 
the deviations mentioned. If a comparison of the calculated with the 
observed deviations should confirm the validity of the law of corre- 
sponding states for the mixtures considered here, then from an expe- 
rimental point of view it would be important to reduce the deviations 
caused by admixture in a whole series of observations to the two 
constants mentioned. These latter can be derived from observations 
on the mixture itself, and we might especially avail ourselves of 
this in calculating observations on substances which can be purified 
only with great difficulty or not at all. 
In this communication I will develop in the first place by means 
of the law of corresponding states applied to mixtures, the relation for 
the proportion of the compositions of the co-existing phases when small 
admixtures occur. This relation will then be tested by HaRTMAN’s obser- 
vations on the composition of co-existing phases in mixtures of methyl 
chloride and carbon dioxide. Lastly formulae will be derived for the dif- 
ference of the saturation pressure of the mixture and that of the pure sub-- 
stance together with the increase of pressure at condensation of the 
mixture. These formulae also enable us to derive the proportion of 
admixture from the increase of pressure observed, after which the 
saturated vapour-pressure of the pure substance can be derived from 
the observed beginning- or end-condensation pressure of the impure 
substance. The latter formula is applied to KUENEN’s observations 
on impure ethane. 
The result is satisfactory in different respects. For the proportion 
of admixture in KUENEN’s experiments corresponding values have 
indeed been found from his different measurements and, moreover, 
from the experiments with the impure substance values for the vapour- 
pressures and the critical data of the pure substance are found which 
can deviate only a little from the real values. 
EE Ea eee ee” 
