28 U. S. BUREAU OF FISHERIES. 



diminution of wearing quality as compared with new white line in the 

 dry condition, (2) copper paints, which give such good results with 

 tensile strength tests, are very poor in their resistance to mechanical 

 wear, and (3) copper oleate leads all the preservatives in mechanical 

 wearing ability upon exposure. 



It is obvious that this factor is highly important in the selection of 

 a proper preservative. The test described may or may not simulate 

 closely the wear that nets receive while in use. Nevertheless, it is 

 mechanical wear and brings out marked and unexpected differences 

 in the several preservatives. It is therefore believed to be of value 

 as a test. 



RESISTANCE TO FOULING BY- MARINE GROWTHS. 



When nets remain in water for a long time, as pound nets, traps, 

 etc., must, they are subject to fouling by growths by barnacles, 

 hydroids, ascidians, algae, etc. These organisms are objectionable 

 for several reasons. Barnacles injure the fisherman's hands and make 

 handling the net difficult; fouling growths cause the nets to resist 

 current and tides, which accordingly causes greater strains on the 

 nets. The weight of the fouling may many times over exceed the 

 weight of the net and therefore greatly increase the strain on it. 

 It is a desirable characteristic of net preservatives that they prevent 

 the accumulation of these growths. 



At Key West, Fla., no noticeable fouling appeared on any of the 

 lines. At Beaufort, N. C, however, fouling proved to be an important 

 consideration. Figures 16, 17, 18, and 19 show the samples of cotton 

 and linen lines that were returned from Beaufort at the end of four 

 months before they were subjected to tests. The key to these is as 

 follows: All of these samples were prepared at the same time, were 

 placed in the water at the same time and place, and were taken up 

 at the end of four months, with the exception of X, which was in the 

 water only one month. 



Sjnmbol and treatment. Condition after four months in water. 



A — White line; no treatment Disintegrated and ,^one. 



F — Coal tar Fouled with hydroids and barnacles. 



G — Pine tar Do. 



H — Pine and coal tar Do 



I — Quercitron and potassium bi- Covered with dense matting of hydroids. 

 chromate. 



J — Petroleum product No. 1 Do. 



L — Dutch method Few hydroids; nearly clean. 



M, N, O, P — Copper oleate Substantially clean; very few barnacles; no 



hydroids. 



Q, R — Copper paints Perfectly clean; no growths. 



S — Gilsonite Fouled with hydroids and barnacles. 



X — Petroleum product No. 2 Fouled, less than petroleum product No. 1. 



This sample had been in water only one 



month. 



XJ — Copper oleate Slightly fouled; some hydroids; no barnacles. 



W — Dutch method Do. 



All the lines that resisted all fouling growths contained copper; 

 that is, those treated with the copper paints, Q and R, and the four 

 copper oleates, M, N, O, and P. The Dutch method, L, containing a 

 very small quantity of copper, was fouled only slightly. All the 

 others that contamed no copper fouled to an objectionable degree, 

 especially quercitron and potassium bichromate, I, and the petroleimi 



