Cavitation, Tensile Strength, and the Surface Films of Gas Nuclei 



1. Monomolecular hydrocarbon and protein films were placed about nuclei 

 produced by cavitation. Most of the film-forming materials used were moderate 

 in price. 



2. The thickest possible hydrocarbon films were used. Thus the resistance 

 of the film to gas diffusion and the strength of the film were the maximum pos- 

 sible, so as to obtain the greatest retardation in dissolving possible. 



3. A few proteins — from those chosen more or less at random as far as 

 knowledge of their structure was concerned — were found to be equivalent to the 

 hydrocarbons in preventing nuclei dissolving. By comparison, this implied that 

 the structure of these proteins had to be of a certain general type. Hence it is 

 unlikely that thicker or "better" protein monomolecular films exist. 



4. The "best" hydrocarbon and protein films reduced the rate of nuclei 

 dissolving from the ideal by almost an order of magnitude. This should be a 

 useful difference. 



5. The lowest "effective" permeability coefficient for gas diffusion (least 

 dissolving) obtained for a monomolecular film placed about a nucleus was 



1.8 X 10"^ cm/sec. This contrasts with the lowest values in the literature of 

 1 X 10"^ obtained under "ordinary" conditions, showing that a film in situ is 

 exceedingly effective in retarding dissolving. 



6. Nevertheless, dissolving of the nuclei was not fully retarded. Tap water 

 in which algae were growing had negligible tensile strength gain due to dissolv- 

 ing. Thus nature had apparently done much better than we had. Since the mono- 

 molecular films used were the best possible, one had to conclude that the only 

 means by which dissolving could be further retarded would be that additional 

 materials must surround the monomolecular film. Therefore a "double" film 

 was devised that prevented virtually all dissolving. 



In doing all this, one obtained a picture of what must take place in nature 

 when a heavy surface film prevents dissolving of gas nuclei. That is: 



1. A monomolecular film must form from organic surfactant material. 



2. The film must have a structure built upon it by gel-like materials which 

 are in themselves nonsurfactant. 



3. The molecular bonds formed must be weak and shear readily, so that 

 each type of material retains its original characteristics as the water moves 

 and flows, so as to be able to act when a nucleus is encountered. 



COMMENTARY 



It has been shown that surface films that retard the dissolving of nuclei 

 come from trace organic materials normally considered insoluble. The term 

 "trace materials" implies considerable variability in the ability of water to 

 form surface films, as has been found to be the case. It is reasonable to expect 



105 



