Cavitation (Influence of Free Gas Content) 
form was dried in the chamber and then removed. When a small 
quantity of water was applied to the surface, it immediately spread 
and then appeared to dry as a film. Later applications of water also 
spread over the surface. 
Plastic bodies made of Delrin were also coated with colloidal 
silica. However, since the plastic has a weak negative charge na- 
turally occuring on the surface, a special positively charged colloi- 
dal silica** was used. After cleaning the surface and applying the 
positive sol, the water also spread over the solid surface and appear- 
ed to dry as a film. 
Both the plastic and the gold plated bodies were then immersed 
in a container of water distilled from a potassium permanganate 
solution to minimize organic surfactant material from contaminating 
the coatings. The bodies were installed underwater while still in the 
pure water of the container. The test results comparing the coated 
with the uncoated bodies are given in Table l. 
** Positive Sol 130M, manufactured by E.I, Dupont de Nemours and 
Co., Wilmington, Delaware. 
Li55 
