Cavttatton (Influence of Free Gas Content) 
water increased significantly as the dissolved gas content was reduced. 
However, after filtering the water through an 0.2 um filter, the 
threshold was then essentially independent of the air content for un- 
dersaturated water. For organic liquids, the threshold was high and 
was not affected by filtering. Hayward [3 1] used a ''tension mano- 
meter'' to produce a tension in the liquid of 0.15 bar. Various li- 
quids were tested by measuring the number of bars prepressuriza- 
tion a sample would have to be subjected before it could withstand the 
0.15 bar tension in the device. Nine organic fluids, including a 
water-in-oil emulsion, were tested and all were found to withstand 
the test tension with no prepressurization required. Of the liquids 
tested, only water was affected by the prepressurization and Hayward 
concluded that only water contained cavitation nuclei capable of sta- 
bilization. A further result was that distilled water (of unstated qua- 
lity) and polluted river water both required approximately the same 
level of prepressurization. These experimental results are consider- 
ed typical of the efforts directed toward understanding the role of the 
particulate in the cavity nucleation process. 
In the case of hydrodynamic cavitation where the body is mo- 
ving in a stationary fluid or conversely, a fluid is moving pasta 
stationary body, an important consideration is how these hydrophobic 
particles are produced and why they remain suspended in the water. 
As has been pointed out by Plesset [4] , if the solid particles have 
densities in the range of 2-3 gm/cm? , then their radius must be 
on the order of 0.01 wm to remain suspended in quiescent water. On 
the other hand, unwetted particles of this size would require a tension 
on the order of approximately 100 bar to nucleate cavities. 
Before this subject of the Harvey model of cavitation nuclei is 
pursued further, some recent oceanographic research pertinent to 
this subject should be considered. Sutcliffe, et al [34] have found 
that aeration of filtered sea water will produce a suspension of inso- 
luble organic particles. Some of these particles eventually settled 
out after aeration but most always remained in suspension. A signifi- 
cant amount of this particulate was larger than the 0.43 mum pore 
size of the filter. It was found that large surface-active organic mo- 
lecules adsorb at the air/water interface of the bubble to produce a 
monomolecular layer. This layer can be aggregated into insoluble 
organic particles by folding into polymolecular layers to form colloi- 
dal micellae or by collapsing into fibers. Coalescence of these colloi- 
dal particles then produce a semistable suspension of organic mate- 
rial. Riley [35] has confirmed the Sutcliffe, et al, work by also 
producing through aeration insoluble particulates from the dissolved 
organic matter in the sea. He also found that the aggregates will in - 
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