Appendix 1 



PERMEABILITY OF POLYETHYLENE BOTTLES TO SEA 



WATER 



General. The Coast Guard Oceanographic Unit collected, in 

 polyethylene bottles, sea water samples from the Davis Strait-Baffin 

 Bay area in late July 1962 and made salinity determinations of these 

 samples in late September, after 2 months' storage. (See Bulletin 

 No. 48 of this series.) 



R. A. Cox (1954), using pure water, has shown polyethylene to be 

 permeable to water, whereas V. Romano vsky (1954), using sea water, 

 indicated that the permeability was to the solution. Another consid- 

 eration is that thermal expansion or contraction within the bottle 

 caused by ambient temperature changes results in a pressure differen- 

 tial on the bottle walls. In addition, osmotic pressure may cause a 

 transfer of water if the exterior of the bottle were contaminated by 

 salt, as usually occurs in the field. Under such conditions condensa- 

 tion of atmospheric moisture at temperatures below the dewpoint or 

 deliquescence of the contaminating salts are mechanisms for forming 

 droplets to produce the solutions on the exterior of the bottle, whose 

 wall may be considered a semipermeable membrane. In veiw of this 

 latter consideration and the opposing conclusions by Cox and Roma- 

 no vsky regarding the salinity change of samples stored in polyethylene 

 bottles, further similar observations were made under varied 

 conditions. 



Experimental. Fifteen polyethylene bottles of approximately 250- 

 ml. capacity, with a shape similar to that described by Romanovsky, 

 were filled to just below the neck from a common sea water source and 

 then set aside in three groups. At the same time, three glass citrate of 

 magnesia bottles (approximately 350 ml.), the type normally used for 

 salinity samples by this Unit, were filled from the same source. 



Group 1. The outside of six of the polyethylene bottles were 

 contaminated with the fill water and were then allowed to sit unpro- 

 tected (with lids screwed tight), subject to the ambient temperature 

 and pressure. This procedure most nearly duplicated field collection 

 and storage conditions. 



Group 2. The exterior surfaces of three polyethylene bottles were 

 carefully cleansed to remove all contamination. After filling, the 

 bottles were placed in a dry bottle sterilizer with a tight-fitting lid 



731-298 O — 64 6 



