1918] 



on Studies on Liquid Films 



401 



into a small quantity of soap solution in the bottle, and then witl) 



drawing it gradually as the gas current 



expanded it to the desired position. 



The tube was then pulled just through 



the film, the current nearly slnit off, 



and the whole left to settle until tlie 



l)lack zone had developed sufficiently 



in the film. The gas to be circulated 



was then connected and turned on, 



and the movements of the film noted. 



The end of the outlet tube was kept 



within a cm. of the film surface to 



maintain a thorough circulation. 



With hydrogen in the vessel, and 

 when the film was half black and half 

 silvery (next in thickness to black), 

 and air was circulating at 130 c.c. per 

 minute, the volume enclosed by the 

 film decreased at a fairly uniform rate 

 of 1 litre in 20 minntes. After this 

 the movement became slower as the 

 percentage of hydrogen diminished in 

 the space beyond the film. Finally, 

 5*70 litres of hydrogen originally 

 present were found to be replaced l)y 

 1 • 40 litre of air. In another experi- 

 ment, with the film almost completely 

 black, G • 28 litres of hydrogen diffused 

 out and were replaced by I'So litre 

 of air. 



The maximum rate of diffusion 

 coidd not be realised in this wide 

 vessel because of the film distortion 

 that was produced when the rate of 

 circulation was increased. To over- 

 come this a vessel only 8*5 cm. in 

 diameter was used (Fig. 37), in which 

 the ordinary stopcock was replaced 

 by a two-way cock A, while an inlet 

 and outlet fitting was fixed in the 

 rubber stopper. The outlet tube as 

 before could slide easily in its air- 

 tight neck. The vessel was filled 

 with hydrogen coming in through A 

 and leaving at B. The film was 



obtained (after first moistening the walls of the vessel) by tilting a 

 drop of the soap solution into the neck at A. The gas entering there 



