fields,* an alternate approach appeared more feasible. It consists of calculating the motion 

 of the bubbles in variable pressure fields from a knowledge of bubble drag at various constant 

 pressure gradients. Experimental data on the drag of air bubbles at various pressure gradients 

 are essential in this procedure. However, only data on the motion of bubbles in pressure gra- 

 dients produced by gravity were available. Therefore, information on bubble motion in water 

 at pressure gradients other than gravity became necessary. This information could be obtained 

 by investigating the rise of bubbles in liquids having the same physical properties as water 

 with the exception of the density. With all other properties of the liquids identical, varying 

 the density would be equivalent to varying the pressure gradient. This approach, however, is 

 not practicable, since there are no liquids available which possess such properties. The 

 other approach is to investigate the rise of air bubbles in various liquids having different 

 physical properties and then to attempt to correlate the results in terms of nondimensional 

 parameters. The available information on the rise of bubbles in different liquids was too 

 meager to allow definite conclusions regarding the significance of the parameters suggested 

 by Reference 1. The present investigation was therefore initiated with the purpose of deter- 

 mining the nondimensional parameters for bubble rise by investigating bubble motion in a 

 number of liquids of different physical properties. If it were found that the motion of air bub- 

 bles rising freely in a liquid, that is to say the motion in the pressure field produced by gravi- 

 ty, could be described, for example, in terms of the drag coefficient, the Reynolds number, 

 and the parameter M(= g y. /pa 3 ),** the results thus obtained could be used in evaluating the 

 drag of bubbles in water at pressure gradients other than that produced by gravity. To do 

 this it would have to be shown that the nondimensional parameters used for the freely rising 

 bubbles are also applicable to other pressure fields. This might be accomplished, for example, 

 by comparing the results of a bubble experiment in water in a nongravity pressure gradient 

 with the results of bubbles rising freely in various liquids at identical "M" number. 



By conducting the tests on the rise of bubbles in various liquids in a large tank, the 

 possibility of the effect of the tank walls on the velocity of the bubbles is eliminated. Since 

 the high cost of many desirable liquids makes the use of a large tank impractical, it became 

 necessary to determine the possible effect of the walls on the velocity over the range of bub- 

 ble sizes to be tested. This investigation consequently acquired two purposes: 



1. The determination of the effect of variation of liquid properties on the motion of air 

 bubbles. 



2. The evaluation of wall effect. 



♦Exploratory experiments of such a nature are reported in Reference 35. 



**This parameter is given in a more general form as (fi Vp)/(p \ a ' ) (where Vp is the pressure gradient; for a 

 gravity field Vp = p g). Therefore, for a specific liquid, it is proportional to the pressure gradient 



