1893.] Gravity of Fluid Bubbles through Liquids. 23 



In this way the surface tension between two liquids, even though 

 they dissolve each other in all proportions, may be measured. Thus, 

 a bubble of water can be got to ascend a tube of glycerine, preserv- 

 ing for a considerable distance its perfectly distinct shape. In this 

 fashion I have found 6*5 dynes per cent, for the initial value of the sur- 

 face tension between water and glycerine. The velocity of the bubble 

 rapidly increases as it proceeds, owing to the surface tension dimin- 

 ishing according as glycerine dissolves in the water. The continuous 

 replacement of one of the liquids in the method gives it an advantage 

 for such a purpose as this over any statical method. The quantity 

 here discussed would in all likelihood prove to be related to molecular 

 rates of diffusion, and perhaps should for this reason merit consider- 

 ation. 



An important point, which up to this has not been touched upon, 

 is the necessity for the liquid of which the bubble is composed not 

 to adhere so tenaciously to the walls of the tube as to cause the 

 bubble to retain the shape shown in fig. 2 in section. This cannot 



FIG. 2. 



happen when the resolved component parallel to the axis of the tube 

 of the tension of the surface between the liquids plus the tension 

 at the surface of separation of the bubble and tube exceeds that 

 between the second liquid and tube. Even though this be not the 

 case, the bubble will often assume the shape with convex ends suit- 

 able for travelling through the tube. 



With every substance, as the diameter of the column is reduced, a 

 stage is reached when there is a tendency to stick even though the 

 end be convex. 



This limit is found to depend largely on the surface tension ; with 

 high values of surface tension it is soon reached. For instance, a 

 bubble of mercury sticks hopelessly in a tube of glycerine of 

 diameter 0'31, while creasote travels freely, although the pressure 

 driving it is 62 times less. Now the surface tension in the case of 

 mercury is 180 times that of the creasote used in these experiments. 



No quantitative determinations have been made on the remaining 



