472 
MR. T. H. LABY ON THE SUPERSATURATION AND 
more efficient nucleus for the condensation of water vapour than the positive, for in 
this case the field of the negative nucleus due to the ionic charge is in the same 
direction as that due to the double layer ; while for the positive nucleus these fields 
are in opposite directions. In the first case the effect of the charge in making the 
ion efficient as a condensation nucleus is increased, and in the second it is diminished. 
Thus the double-layer theory requires, in order to account for the observed greater 
efficiency of the negative nucleus than the positive, that the negative layer on a water 
drop should be next to the water and the positive layer next to the air. This we 
have seen is also the arrangement of the layers to be expected from the fact that 
water becomes positively charged when bubbled. In other words, this theory requires 
that the sign of the charge acquired by air, when it is bubbled through a liquid, 
should be the same as the sip'n of the charge on the more efficient nucleus for the 
condensation of the vapour of that liquid. 
The eleven liquids mentioned on p. 471 have been found by Przibram and myself 
to condense on the positive nucleus more readily than on the negative. In the case 
of these substances the theory requires that when air is bubbled through them the 
liquid should become negatively charged. When the liquids were bubbled, all that 
were tried, with exception of acetic acid, became negatively charged in agreement with 
the theory. 
Ethyl alcohol is the only one of the liquids which had been previously examined in 
this way ; Lenard found in two experiments with alcohol containing 9 per cent, of 
water the electrification on bubbling to be once — 0 - 039 and once +0T23 in terms of 
his unit. 
In the writer’s experiments a small wide-mouthed bottle was insulated by attaching 
it with sealing wax to a disc of vulcanite. A foot bellows, which gave a sufficiently 
uniform pressure, forced air through two tubes containing cotton wool, calcium 
chloride, and solid caustic soda. The dust-free and dry air passed through a 
vulcanite tube insulator to a glass tube which dipped below the surface of the liquid 
in the bottle. When the bellows were in action, a steady stream of bubbles was 
formed in the liquid. The electrification produced was detected by attaching a wire 
dipping in the liquid to one pair of quadrants of a Dolezalek electrometer which gave 
from 4000 to 5000 nuns, deflection per volt on a scale at about 2 meters. The bottle 
and wire were shielded from inductive effects by an earthed metal vessel. The drift 
of the spot was generally observed for four minutes while the air was bubbling 
through the liquid and for the same time without bubbling. The difference in the 
drift gave the electrification due to the bubbling. For nearly all the liquids tried the 
effect was larger the first time the liquid was bubbled than for subsequent bubblings. 
lor methyl and ethyl alcohols the electrification was small and could just be detected 
with certainty. 
It was found that different samples of Kahlbaum’s I methyl alcohol, which had 
been distilled after drying over lime, became sometimes positively and sometimes 
