404 



Professor Sir James Dewar 



[Jan. 18, 



an 8 cm. bul)l)le in a vessel charged to 7 atmospheres took 4 months 

 to diminish 1 cm. in diameter, the same contraction at atmospheric 

 pressure taking only about 14 days. 



Suitable vessels for these measurements are afforded by the strong 

 glass bottles used to hold sulphurous acid. A screwed brass collar 



was cemented to the neck, and to 

 this a brass T -piece was secured 

 by a gas-tight union. The glass 

 nozzle for supporting the bubble 

 was cemented into the vertical 

 arm of the T-tube, and sealed to 

 a thick glass bulb above bent 

 over horizontally to hold some 

 soap solution. The gas used was 

 admitted by the valved horizontal 

 arm of the T-piece, a hole being 

 made at this level into the inner 

 glass tube to give access through 

 the nozzle, which had a diameter 

 of about 1 cm. (Fig. 39). Just 

 within its lower end a constriction 

 was formed. The apparatus was 

 tested and found tight under 10 

 atmospheres pressure. 



The pressure was first ad- 

 justed to about 6 atmospheres, 

 and a drop of soap solution was 

 decanted into the constriction ; 

 on admitting more gas a bubble 

 was expanded on the nozzle and 

 the pressure thereby raised to 6J 

 atmospheres. The black stage 

 then developed very much as 

 usual, and the gas transference 

 was determined by periodic mea- 

 surements of the contraction. 



Table V. gives the rate of 

 transference obtained in hydro- 

 gen at C)^ atmospheres compared with the values at 1 atmosphere. 

 The numbers given are calculated for diameters of 4, 6 and 8 cm. 

 The second column gives the internal excess pressure P of the soap 

 bubl)le (in mm. of water) measured at atmospheric pressure. The 

 proportion F of this to the total pressure in the bu])])le vessel is 

 shown in the third column (in units of 10"") both for 1 atmosphere 

 and G-^ atmospheres. The ol)served rates of gas transference K, are 

 similarly shown in the fourth column. 



Fig. 39. 



