186 Professor Sir James Dewar [Jan. 19, 



solution supply was stopped the development continued to the l)lack 

 state. When completely black the Avhole mass, in a bubble 40 cm. 

 in diameter, is of the order of 50 mgms., so that the bubbles are 

 very susceptible to disturbance from shock to the containing 

 vessel. Local or sudden changes of temperature must also be 

 avoided, as strong convection currents are thereby set up. Such 

 currents become evident by innumerable silvery discs (see p. 1*3) stream- 

 ing continuously in many directions over the black film. The thicker 

 silvery discs floating for a time on the thinner black film represent 

 excess of liquid drawn in either from the drop below or the ring 

 of liquid, at the contact of the bubble with the supporting nozzle. 

 By the use of closed vessels the nozzle is kept constantly moist, and 

 this is probably a factor in the preservation of black bubbles. 



DuEATioN OF Life of Various Bubbles. 



The records of a large number of bubbles, up to 16 cm. in 

 diameter, have been preserved. Some extracts are condensed in the 

 following summary : — 



Table 1. — Lives op Various Bubbles.* 



Three, 16-18 cm., 50 per cent, glycerine, 5 -pev cent. soap,\ oa 4o ,^ 

 water in vessel ; temp. 10°-20^ C. / ^^"^^ ^^^'^• 



One, 14 cm., 50 per cent, glycerine, Idt per cent. soap,l go 

 water in vessel ; half black at end ; temp. 4"-ll^ C. j " 



One, 20 cm,, 50 per cent, glycerine, 5 per cent, soap;! q^- 



30 



temp, 9"-ll° C, ; over 60 per cent, black at end 

 One, 12 cm., 30 per cent, glycerine, 3 -per cent, soap 



temp, 10°-20° C. 

 Black horizontal film, 20 cm. diam,, 50 per cent, glycerine, | 



5 per cent, soap ; temp. 4-20° C, ' / °^'®^* ^ ^'^^^"* 



Table 2, — Life of Successive Bubbles. 40 cm. Bubbles on Einsf, 



* A hanging bubble kept in air saturated with water vapour, of an initial 

 capacity of 4 • 5 litres, took 322 days to completely collapse from air transfusion. 



