RESISTANCE OF MATERIALS TO MARINE BIOLOGICAL ATTACK 1103 



Of course, air bubbles would be a source of error in later oxygen deter- 

 minations. 



Usually, sufficient test bottles are made up to provide duplicates for 

 analysis after each period of incubation. Oxygen pressure, maintained 

 on the sea water in the carboy, assures no loss of oxygen from the me- 

 dium and forces it through tubing into the test bottles. Since incubation 

 periods of 0, 1, 2, 4 and 8 weeks are used as a general guide, and two test 

 bottles must be sacrificed for analysis after each interval, ten test bottles 

 are used for each material. One set of ten control bottles containing only 

 inoculated, aged sea water suffices for a test run, as long as the bottles 

 for materials and controls are made up from the same batch of sea water 

 and incubated at the same time. Incubation is carried out in the dark 

 in a constant temperature water bath maintained at 20° dz 0.5°C. 

 Incubation in the water bath minimizes the fluctuation in ox^'gen content 

 of the sea water which might be encountered as the result of "breathing" 

 of the bottles in atmospheric incubation. After the various incubation 

 periods, the free oxygen content of the sea water in the bottles is deter- 

 mined by a modified Winkler procedure. 



In the anaerobic portion of the test, the procedure is essentially the 

 same as for the aerobic part, the only differences being in the prepara- 

 tion and handling of the sea water medium, the incubation times, and the 

 analytical method. Of course, with the anaerobic bacteria it is necessary 

 to remove all free oxygen from the sea water medium if the organisms 

 are to function. Consequently, instead of bubbling oxygen through the 

 medium, the sea water is boiled for ten minutes and placed hot in a 



Table IV — Oxygen Consumption by Marine Bacteria 



IN BOD Test with Polyethylene as the 



Only Source of Organic Carbon 



Test Material- 



2.0 melt index^ 



0.2 melt index (Source A) 



0.2 melt index (Source B) 



0.2 melt index + antioxidant 



0.2 melt index -j- 5% butyl rubber -|- antiox. 



0.7 melt index (High Density) -f- antiox 



Controls (inoculated sea water) 



O2 Consumption .\fter Weeks of Incubation 



ppm 



2.2 

 0.8 

 1.4 

 0.9 

 0.2 

 0.9 

 1.5 



ppm 



3.7 

 1.6 

 3.4 

 3.0 

 3.8 

 4.3 

 5.3 



ppm 



6.0 

 2.4 

 5.2 

 6.2 

 5.8 

 7.4 

 8.3 



8 



ppm 



10.2 



10.9 



10.8 



8.5 

 1 



9.3 

 11.2 



' Samples accidentally destroj-ed. 



- Except where noted polymers are low density grades manufactured by the 

 high pressure process. 

 3 ASTM D123S 



