ORIGIN OF THE SMALL BUBBLES OF FROTH. 219 



liminary to the disruption of the surfaces. Such an origin 

 would ensure to the small bubbles that layer of contamin- 

 ation essential for their stability, and the explanation 

 of their production, here suggested would thus account 

 for their uniform durability. 



Owing to the circumstances of the development, the 

 exact manner of the creation of these small bubbles must 

 remain a matter of some conjecture, and the foregoing 

 description is put forward in no other sense. The surpris- 

 ing feature, which requires explanation, is the fact that 

 the addition to a solvent, which alters the effect of its 

 agitation from a few evanescent bubbles to a dense lasting 

 froth, may involve, in the value of the surface tension, a 

 diminution, under isothermal conditions, of only about one 

 per cent., an amount altogether too small, if taken by itself, 

 to be considered as changing the conditions. 



The small bubbles, here under review, are characteristic 

 of 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 

 of 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 cases, as may be seen by a comparison of the 

 photographs, the bubbles belong, as a whole, to a much 



