Electric Current on the Thinning of a Liquid Film. 95 
at one time the black would appear after a comparatively short 
interval; at another, the film would persist for many hours 
without showing a trace of black. As at this time our atten- 
tion had not been directed to the possible influence of the 
current itself in modifying the rate of thinning of the film, no 
special precautions were taken with regard to the current, 
either as to its direction or intermittence ; but we now know 
that the apparently capricious behaviour of the films observed 
on many occasions was largely, if not entirely, due to want of 
method in managing the current. 
We have recently made some experiments with the definite 
object of determining the effect upon a liquid film of passing 
through it a current of electricity. Some of the results 
obtained were communicated to Section A of the British 
Association at the Montreal meeting. We propose to give in 
this paper a somewhat more detailed account of our obser- 
vations. 
The liquid employed consisted either of a solution of potash 
soap in water, or of Plateau’s liquide glycérique, containing a 
certain proportion of nitre to increase its conductivity. The 
films had the form of vertical cylinders, the upper and lower 
ring supports being of platinum, and about 33 millim. in 
diameter. ‘The cylinders were generally either 30 or 40 
millim. long. Occasionally other lengths were employed. 
Three films were under examination at the same time; two 
being in one glass box, the third in a separate glass box. 
The two that were together were supported by platinum rings 
identically alike and sharply bevelled at the edge; the edges 
of the supports of the third were much thicker and were 
rounded. We had thus the means of ascertaining whether 
any difference in the behaviour of the films was due to the 
form or thickness of their supports. No such difference was 
observed. 
Hach of the film-boxes was placed in the centre of a water- 
tank with giass sides, in order to prevent rapid changes of 
temperature. In all cases the films were surrounded with air 
saturated with the vapour of the liquid of which they were 
made. The constancy of the hygrometric state of the air, 
and that of its temperature were indicated respectively by a 
hair-hy grometer and a thermometer inside the glass case. 
The films were blown with air which was first dried and 
then passed over some of the soap-solution in a wide tube. 
The state of the air inside the film was thus approximately 
the same as that on the outside. ; 
In the earlier experiments a battery of nine Leclanché cells 
was used, the electromotive force of which was about 12 volts. 
