Bernd 



The mixtures, although effective in preventing dissolving, had short life. 

 This is shown in Fig. 14a, where successive tests using the same samples show 

 increasingly higher tensile strengths. One might possibly attribute this increase 

 to attrition of the film forming materials, or to a protein film becoming insolu- 

 ble. However, just allowing the sample to stand had a similar effect (Fig. 14b). 



SUCCESSIVE TESTS 

 a. SUCCESSIVE TESTS ON SAME SAMPLE 



DAYS AFTER MIXING 



. ALLOWING SAMPLE TO STAND 

 (NEW SAMPLE FOR EACH TEST) 



STIRRED PRIOR TO 

 -^CAVITATING 



SUCCESSIVE TESTS 

 c. EFFECT OF STIRRING 



Fig. 14 - Double film formation 



Therefore, suppose one assumed that this decrease in film formation is due 

 to bonding taking place between gelatin molecules, or between gelatin and sur- 

 factant to alter the character of the surfactant, thereby preventing films from 

 being formed. Bonds so formed probably would be weak. In that case shearing 

 of the fluid as it is stirred might be able to break the bonds. Stirring did in fact 

 improve a sample, and did partially restore its film-forming activity (Fig. 14c). 

 This substantiated the chain of reasoning. However, weaker bonds and/or a con- 

 tinuous shearing motion are apparently needed to maintain the water in its orig- 

 inal condition of preventing dissolving. 



Summation 



In investigating the surface films of gas nuclei, the following steps were 

 achieved: 



104 



