754 
Messrs. Owen and Hughes on Molecular 
inaccuracy in the estimation of the composition of the mixture 
due to the 4 cms. of gas originally in the globe, it is once 
more exhausted and the gases mixed as before. The results 
obtained show that this precaution was unnecessary as the 
effects change but slowly with the composition of the mixture. 
The latter could be drawn into the apparatus (see fig. 2) 
at approximately atmospheric pressure by connecting the 
globe B to the atmosphere through the tap A. About twenty 
tests could be performed with the mixture before the supply 
in the globe C became exhausted. By means of a side path 
(not shown) pure air could be drawn into the apparatus for 
purposes of comparison. 
Air and Carbon Dioxide. 
The following table summarizes the results obtained in 
mixtures of air and carbon dioxide. 
Table IV. 
"Sudden" Method of Cooling. 
Temperature. 
Pure Air. 
- 86o 
C 

- 92 

- 96 

-127 
Few drops. 
-128 
Thin shower. 
-190 
Tinted cloud. 
5 per cent. CO.,. 50 per cent. C0 2 



Few drops. 
Thin shower. 
Tinted cloud. 
Fair shower. 
Good shower. 
It will be seen from the above table that the effects in pure 
air and air mixed with 5 per cent, of C0 2 are indistinguishable 
both in respect to the value of the " nucleating temperature " 
and to the magnitude of the effects obtained. 
In the above experiments the mixture was maintained at 
a pressure of 80 cms. Thus the partial pressure of the C0 2 
in the 50 per cent, mixture at atmospheric temperature was 
40 cms. At this pressure the condensing temperature is 
approximately —85°; on cooling down, however, the partial 
pressure of the C0 2 when near the condensing point would 
be less than 40 cms., and therefore its condensing temperature 
would be somewhat below —85°. Now from the above table 
it is seen that the effect in the 50 per cent, mixture starts 
somewhere between — 86° and — 92°. On making allowance 
for the reduced partial pressure, it is seen that C0 2 in the 
