752 
Messrs. Owen and Hughes on Molecular 
nuclei" (such as those produced by intense ultra-violet 
light) in which clouds are formed without any supersaturation 
at all. 
Ethylene. 
Ethylene was prepared by the action of pure alcohol upon 
syrupy phosphoric acid and was passed through a condenser 
in ice, a strong solution of caustic potash, concentrated sul- 
phuric acid, and P 2 5 . It was then condensed in the tube as 
described in the section on C0 2 . After this liquefied gas had 
been allowed to boil under reduced pressure for a short time 
to remove auy air or carbon monoxide, a quantity was dis- 
tilled over into a second evacuated tube surrounded by liquid 
air until two-thirds of the liquid ethylene in the first tube had 
evaporated, the remaining third being rejected. Thus the 
second tube (our gas-holder for these experiments) contained 
ethylene of a high degree of purity. 
The following summarizes the effects obtained : — 
(1) The gas which comes off liquid ethylene is quite 
nuclei-free. 
(2) No nuclei are produced in ethylene when cooled either 
by the "sudden" or the "slow" methods. The 
temperatures tried were —95°, —110°, —145^ and 
— 190°, condensation taking place at the last three 
temperatures. 
Thus there is no " nucleating temperature " for ethylene. 
Methane. 
Methane was prepared by heating sodium acetate with 
soda lime. The gas was passed through caustic potash, strong 
sulphuric acid, condensed and distilled as in the case of 
ethylene. 
The following results were obtained : — 
(1) The gas which comes off liquid methane is nuclei-free. 
(2) Table III. gives the results obtained in methane by the 
" sudden " method of cooling. 
Table III. 
Temperature. 
Effect. Tester Y. 
— 
-97° C 
0. 
Few drops. 
Thin shower. 
Good shower. 
Tinted cloud. 
-102° 
-107° 
-112° 
-131° 
