30 U. S. BUEEAU OF FISHERIES. 



Table 10. — Tensile strength of linen lines exposed to sea water at Beaufort, N. C. 



Symbol and treatment. 



Number of months 

 exposed. 



Tensile strength in pounds. 



T — Untreated control 



U — Copper oleate solution 12J per cent in gasoline, 5 per cent oil 



V — Quercitron and potassium bichromate 



"W— Dutch method 





1 Average of 50 breaks; every other figure in this table is the average of 15 breaks. 

 * Line was disintegrated and gone. 



The conclusions from these tests are obvious: Linen lines, with or 

 without preservatives, disintegrate more rapidly than cotton lines 

 under the same conditions in salt water at Beaufort, all four samples 

 having disappeared before the term of six months expired. Only 

 the two samples that contained copper — that is, copper oleate, U, 

 and the Dutch method, W — lasted four months, the one preserved by 

 the Dutch method being then all but totally rotten. At the end 

 of two months the lines treated by either the copper oleate or Dutch 

 method are still serviceable, but the leading score in this experiment 

 easily belongs to copper oleate. 



The principal method of preserving these linen lines on the Pacific 

 coast is barking — that is, treating with the hot extract of oak bark — 

 which treatment is not followed by a mordant. Even when mor- 

 danted, as in quercitron and potassium bichromate, it is plain that no 

 good results are obtained by the use of bark, unless possibly the peri- 

 odical treatment with the infusion merely washes and sterilizes the 

 net for the time being. When bark is mordanted with ammoniacal 

 copper sulphate (Dutch method), considerable good is done; but this 

 metnod is much more laborious and time-consuming than the appli- 

 cation of copper oleate and not so effective. Washing the nets in 

 bluestone (copper sulphate) solution, as done on the Pacific coast, 

 may serve to keep the lines clean, but because of its solubility blue- 

 stone can not be a permanent preservative. The regular use of copper 

 oleate in the salmon gill-net fishery should effect a marked saving 

 in nets. 



SUMMARY OF RESULTS OP BEAUFORT EXPERIMENTS. 



1. The materials and preservative methods studied at Beaufort 

 were : For cotton lines, copper oleate in four variations, coal tar, pine 

 tar, coal tar and pine tar mixed, quercitron and potassium bicmo- 

 mate, petroleum products Nos. 1 and 2, Dutch method, copper paints, 

 Nos. 1 and 2, and gilsonite; for linen lines, quercitron and potassium 

 bichromate, Dutch method, and copper oleate, 12^ per cent solution. 



2. In the preservation of tensile strength of cotton lines the copper 

 paints, which contain heavy concentrations of copper, excelled. Cop- 

 per oleate, in the concentrations tried, which were much less than 

 those of copper paint, was next in order of superiority; the Dutch 

 method, also containing copper, was third; the tars were fourth; all 



