Origin of the Small Bubbles of Froth. 193 



the froth which is produced by violent agitation, and are not 

 dependent on the method which is used for introducing the 

 gas into the liquid. It is considered that, in all cases, they 

 are the results of the disintegration of the surfaces of larger 

 bubbles, the essential condition for their creation being the 

 development, on these surfaces, of spots of diminished surface 

 tension, associated with a gas pressure within the bubbles 

 considerably in excess of that required for equilibrium in the 

 circumstances existing at the moment of disruption. 



It yet remains to consider the production of the bubbles 

 formed by processes which are independent of the nature ot 

 the liquid used, such as those which result from the breaking 

 up of a jet of gas when forced into uncontaminated water, or 

 into a solution which does not yield a lasting froth. In these 

 case, as may be seen by a comparison of the photographs, the 

 bubbles belong, as a whole, to a much larger class than 

 those in the acetic acid solution whose origin has just been 

 considered. 



The larger of the bubbles of the class now under discussion 

 are created by the partition of the volume of gas entering 

 the liquid, considerable portions of the gas being " pinched 

 off/' as it were, by the action of currents in the liquid, or, 

 having lost their downward momentum, becoming separated 

 from the mass of inrushing gas owing to their buoyancy. 

 Bubbles made in some such way are always created when a 

 liquid of any kind is agitated, and the class includes the 

 largest of the bubbles which are produced by any method of 

 disturbance. 



But there are other bubbles of the same general class, 

 though much smaller, whose development follows a more 

 orderly course. These are shown in various stages of their 

 growth in the photographs of Plate VIII,, the reference being 

 to bubbles from about a tenth to a few millimetres in 

 diameter in many cases still attached to the parent 

 surfaces. 



Figure 6, Plate VIII. shows clearly two of the bubbles in an 

 early stage of development, still part of the lower surface of 

 the bubble caused by a jet of carbonic acid entering a O'l per 

 cent, aqueous solution of acetic acid, the pressure of the gas 

 being too low to cause the disintegration of the surface of the 

 main bubble. Figure 7 is a photograph of a bubble of 

 carbonic acid being formed in water, and figure 8 one of a 

 bubble of the same gas in a O'l per cent, aqueous solution 

 of sulphuric acid, 



Whatmough * shows that dilute aqueous solutions of 

 * Whatmough, he, cit, 

 Phil Mag. S. 6. Vol. 24 No. 139. July 1912. 



