Jan. 18, 1018] 



Studies on Liquid Films 



367 



qiiently encounter little resistance, and dovelope rapidly, linking up 

 into a glittering lustrous froth which increases until the globe is full. 

 Excess liquid drains away very rapidly, the black stage being reached 

 in about an hour. The beauty of the mass can be seen properly 

 only when a beam of liglit is flashed upon it in continually changing 

 directions, the different inclinations of the internal plane films giving 

 rise to a continuous series of brilliant scintillations (Fig. Sa). The 

 same appearance is perhaps still more remarkable when the mesh- 

 work is lit up by diffused light from rays thrown across the observer's 

 line of vision (Fig. 36). A black background is used in both cases. 



The internal walls of the various cells being plane polygons, the 

 pressure of the air in these cells is the same for all, and is regulated 

 according to the curvature of the cell-walls on the outer boundary. 

 As transference of the enmeshed air from the mass can take place 

 only through the curved boundaries of the outer layer of bubbles, 

 contraction of the mass from this cause is 

 relatively slow. In one case it required a fort- 

 night for the initial volume to be reduced to 

 one half. 



To obtain the best result tlie blowing tube A 

 should be withdrawn when the mesh-work has 

 been completed, as it exerts some protecting 

 power over the bubbles that closely surround it, 

 thus causing an annular depression farther out, 

 and tending to destroy the mass. 



Columns and Chains of Bubbles. 



For the purpose of studying bubble clusters 

 and film complexes, instead of single bubbles 

 and plane films, an arrangement of the nozzle 

 was employed, by which it was possible to get a 

 succession of bubbles of any required volume, 

 linked together, in one operation. The apparatus 

 employed is shown in Fig. 4. A is a stoppered 

 reservoir of soap solution from which a capillary 

 tube passes down the air-supply tube D, B, to 

 about 1 cm. above a constriction K. After 

 passing K the lower end of the air-supply tube 

 is, for convenience, fitted by a ground joint to 

 an enlarged nozzle C, securely held in position 

 by the rubber cork E. The stopper A being 

 opened at regulated intervals of time, a series -^ . . 



of drops falls on the constriction K, which are 

 immediately Ijlown into films by the constant air current entering 

 through the bulb D (protected as before by lightly packed glycerined 

 cotton wool). Hence a series of bubbles is produced at the nozzle C, 



