1917] 



on Soap Bubbles of Long Duration 



191 



down the upper part of the Inibble till it became a neck. When this 

 divided, the disturbance was probably more than the very dilute and 

 very thin film could survive, for the next morning it had gone. 



The seventh bubble in the second vessel was suspended from a 4-cm. 

 nozzle ; it lasted from 27th October to 9th December. The tempera- 

 ture fell from 15° C. at first to below 10° C. after the first week. The 

 bubble burst after a sudden rise of temperature from 6° to over 9% 

 accompanied by a considerable fluctuating fall in the barometer, 

 when it was found, by the optical test, that the air in the globe had 

 become contaminated. This bubble afforded an opportunity for 

 observing the rate of fall of condensation drops. Excluding the pre- 

 liminary drainage, the results are shown in the annexed diagram 

 (Fig. 5). 



^DAtb 



Fig. 5. — Absorption of Water Vapour by a 40 cm. Bubble. 

 Eate of fall of drops. 



GrAS Transference Through Bubbles at 

 Atmospheric Pressure. 



Long-lived bubbles regularly diminish in diameter, and most 

 rapidly when thinned to " black." The contained air or other gas 

 is at a somewhat higher pressure than the atmosphere in which the 

 bubble stands, and therefore tends to pass out ; with the result that 

 there is a continual diminution in size. With black bubbles up to 

 about 15 cm. the change becomes very evident in about a week. 

 Using a cathetometer, the contraction can be observed accurately 

 from day to day. The subjoined diagram (Fig. 6) shows the con- 

 traction, measured every third day, of a black bubble in hydrogen. 

 From an initial diameter of approximately 11 cm., by the twenty- 

 third day it had completely contracted. It will be noticed that the 

 rate of contraction was accelerated as the diameter decreased. 



The gradational diminution in diameter of black bubbles made 

 from soap solutions of different compositions, and with diameters up 

 to 46 cm., was periodically measured with the cathetometer. 



The rate of gas transference from within the bubble outwards at 

 any time can be obtained directly from the mean daily reduction in 

 -diameter at that time, and is readily measured by dy/dx, the slope of 



