PRESERVATION OF FISH NETS 



415 



as to whether or not twine deteriorated more rapidly when con- 

 tinuously or when periodically submerged. The experiment here 

 described was intended to furnish some information regarding this 

 point. The location at Boothbay Harbor was chosen because it 

 afforded facilities at the Bureau of Fisheries hatchery for suspending 

 sample lines in sea water in such a manner that one set would be 

 submerged continuously while a second set, identical with the first, 

 would be submerged only at high tide. 



WATER CONDITIONS AT BOOTHBAY HARBOR 



The average monthly temperatures of the water at Boothbay 

 Harbor over the period of the test are given in Table 2. Salinity 

 records are not available. 



MATERIALS TESTED 



The twine used in this series of tests was of the same kind as that 

 used in the preceding experiments — No. 24 cable-laid hard-finish 

 cotton. The preservatives and preservative methods tested were 

 copper oleate in four variations (EE, FF, GG, and HH) ; quercitron 

 and ammoniacal copper sulphate (L), a proprietary waterproofing 

 (JJ), coal tar (KK), and the coal tar-copper oleate mixture (Y). 

 The lines were measured, weighed, treated, and again measured 

 and weighed, as previously described. The shrinkage and increase 

 in weight will be discussed under a separate heading. 



TENSILE STRENGTH 



The results of tensile-strength measurements on the continuously 

 exposed series are shown graphically in Figure 2. Here it will be 

 noted that coal tar, the copper oleate-coal tar mixture, and all copper 

 oleate samples except the one combined with paraffin preserve lines 

 well throughout the period of exposure. Sample lines treated with 

 the copper oleate-paraffin mixture (FF), the proprietary waterproof- 

 ing (JJ), and the quercitron-ammoniacal copper sulphate preserva- 

 tive (L) lasted throughout the six months' test, but snowed a marked 

 diminution of tensile strength near the end of the period. The 

 untreated line (A) lasted for four months, as against two months 

 at Beaufort, N. C. All sample lines deteriorated much less rapidly 

 at Boothbay Harbor than at Beaufort. 



In Figure 3 are shown graphically the results of tensile-strength 

 tests on the lines that were submerged only at high tide at Boothbay 



78209— 26t 2 



