222 J. A. POLLOCK. 



the larger bubbles. In this case the size and number of the 

 bubbles will depend on circumstances which determine the 

 nature of the liquid movement. 



This suggestion as to the origin of these small bubbles is 

 prompted by the result of the process of exclusion pre- 

 viously outlined, and though impossible to prove, as the 

 turbulence of the liquid cannot be directly seen, is not 

 improbable from the appearance of the detail shown. 



IV. Summary.— The object of the investigation was to 

 find the origin of the small bubbles which constitute the 

 characteristic feature of the froth which is produced by 

 violent agitation. The froth is readily created when gas 

 under pressure is forced into a liquid through the orifice of 

 a vertical pipe, and in order to study the conditions of its 

 formation, instantaneous shadow photographs have been 

 taken of the jet of gas in various solutions. It is seen from 

 an inspection of the photographs, that the bubbles which 

 result from the breaking up of the jet may be separated, 

 with respect to the exact manner of their production, into 

 three classes. 



1. Large bubbles are created by the partition of the main 

 bubble which is being continuously formed on the end of 

 the pipe, considerable portions of the gas being 4 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 incoming gas owing to their buoyancy. 



2. The photographs accompanying the paper show small 

 bubbles which are clearly the result of the detachment of 

 cylindrical protuberances formed on the surfaces of the 

 larger bubbles, the protuberances having lengthened until 

 the state of instability has been reached. These bubbles 

 are seen in various stages of their attachment to the parent 

 surfaces, and are shown to occur in water, and in a non- 

 frothing as well as in a frothing solution. It is considered 



