( 665°) 
In the same way is 
(vq — vd (pap) = MRI (1 —el), . . ws (8) 
if pz is the pressure of the saturated vapour, of the composition «. 
The increase of pressure at the condensation of vapour of the com- 
position « into liquid of the same composition follows therefore from 
(02 — vj) (pi — po) = MRT a (ek Hek — 2) . . . (9) 
§ 5. Equation (9) can serve to determine the composition of the 
substance under examination from measurements on the increase of 
pressure. 
Such measurements have been made by KurNeN !) on the conden- 
sation at different temperatures of ethane, with a small admixture, 
probably of butane. Although these observations are very accurate, 
they are not sufficient to test my formulae with certainty. The 
degree of purity of the ethane itself was not so high that we can 
derive the constants « and /? accurately from the critical data found 
for this substance with those for the mixture of 4°/, butane, while 
the mixture of 9 °%, differs too much from the pure substance for 
us to derive these quantities from the two mixtures. I have tried 
to form an idea of the usefulness of the formulae by deriving from 
these observations the quantity of the admixture, by means of 
Kye bis 
values assumed for —— and —. 
1 J 
These might have been determined from observations on mixtures 
of the two substances in known proportions. But'as such obser- 
vations on these mixtures are not at hand and as for our purpose 
we do not require the very greatest accuracy I have put: 
bi + bop 
9 ’ 
while I calculate Ay), Koo, bij bag from the critical constants of the 
substances, according to the relations mentioned in § 3, borrowed 
from CLAUSIUS’ equation of state: 
K 
n=oV/ = vpk Go of 
where C, and C, have the same value for all substances. 
Then 
Kis = Vig) REN and bye = 
!) Kuenen, Proc. Roy. Soc. Edinburgh 1897, p. 433; Zeitschrift fiir comprimirte 
und flüssige Gase I, p. 153. 
44* 
