PRESERVATION OF FISH NETS 



413 



in the physical properties of the original samples. A rise in the curve 

 at some point during the course of the test must not be taken as 

 indicative of an increase in the tensile strength of the line, but rather 

 of a difference in the tensile strength of the original sample. 



SERIES EXPOSED IN SEA WATER AT BEAUFORT, N. C. 



MATERIALS TESTED 



Cotton-line samples were prepared with each of the following pre- 

 servatives according to the preservative methods described: Copper 

 oleate in four different combinations (EE, FF, GG, and HH), quer- 

 citron and ammoniacal copper sulphate (L) ; the proprietary water- 

 proofing (JJ), coal tar (KK), the copper oleate-coal tar combina- 

 tion (Y), a proprietary wood preservative (LL), azulmic acid (MM), 

 rare-earths treatment (RE), rare earths and copper oleate combined 

 (RC), and untreated line (A) used as a control. Seven samples were 

 prepared by each treatment, one to be held as an unexposed check 

 and the other six to be exposed. The exposures were made in the 

 water of Beaufort Harbor at the wharf of the Bureau of Fisheries 

 biological laboratory from June 1 to December 1, 1923. Water 

 conditions at this point were discussed in the previous report. Tem- 

 peratures and salinities of the water over the period of the test are 

 given in Table 1. 



Table 1. — Water conditions at Beaufort, N. C. 



Year and month 



1923 



June 



July 



August 



September 



October 



November. 



Temperature 



Maximum Minimum Average 



Specific gravity 



Maximum Minimum Average 



1.023 

 1.023 

 1.022 

 1.022 

 1.020 

 1.025 



1.021 

 1.017 

 1.017 

 1.017 

 1.015 

 1.017 



1.021 

 1.023 

 1.020 

 1.019 

 1.017 

 1.018 



TENSILE STRENGTH 



Most of the preservatives here considered caused an immediate 

 decrease in tensile strength of the lines, the exceptions being the 

 proprietary wood preservative (LL), azulmic acid (MM), and the 

 rare-earths treatment (RE) . The results of tensile-strength measure- 

 ments of the individual samples are shown graphically in Figure 1 . 



Upon exposure the preservative (Y), a mixture of copper oleate 

 and coal tar, proved to be a better preservative of tensile strength 

 than any other tested. The sample treated with this material, to- 

 gether with two samples preserved with the copper oleates (EE and 

 GG) and one preserved with coal tar (KK), were the only ones 

 that lasted over a period of six months at Beaufort. The last three 

 were of about equal value. Next in order of diminishing tensile 

 strength come the lines treated with the copper oleate-paraffin mix- 

 ture (FF), copper oleate and raw linseed oil (HH), and the proprie- 

 ,tary wood preservative (LL). Samples treated with the three last- 

 named preservatives were completely rotten at the end of five 



