FISH-NET PRESERVATIVES. 5 



the lines quickly. It preserved tensile strength well in salt water, 

 resisted fouling by marine growths, resisted abrasion or wear as well 

 as any other preservative, increased weight and stiffness only slightly, 

 and imparted an acceptable green color to the line. In fresh water 

 results were less promising. Directions are given for making and 

 using it. 



15. Marked differences in the behavior of lines were manifested at 

 different places and in different waters. At Beaufort, N. C, in salt 

 water, sample lines fouled more heavily and disintegrated more 

 rapidly than they did at either Key West, Fla., or at Woods Hole, 

 Mass. In fresh water of Lake Erie, at Put in Bay, Ohio, the sample 

 lines suffered more rapid deterioration than they did at any place in 

 salt water. 



16. On linen lines quercitron and potassium bichromate, the 

 Dutch method, a petroleum product, and copper oleate were tested. 

 Copper oleate preserved best in both salt and fresh water. The 

 Dutch method was good; the others were worthless. Linen line, 

 with or without preservatives, and in salt or fresh water, deteriorated 

 more rapidly than cotton lines. 



17. In no preservative studied was there detected any tendency 

 toward spontaneous heating or combustion. Such cases of heating 

 of nets as occur must be ascribed to something other than simply 

 the preservative. 



18. Even with highly oxidizable oils, such as linseed oil, the tem- 

 perature necessary to kindle spontaneous heating is in excess of 122° 

 F. (50° C). _ 



19. Cotton lines exposed to temperature as high as 302° F. (150° C.) 

 dry heat, or 257° F. (125° C.) under steam pressure for two hours 

 showed no significant loss of tensile strength. Higher temperatures 

 than these are necessary to produce any weakening of lines. 



20. A mathematical procedure was devised for grading the several 

 materials for all-round usefulness as fish-net preservatives with new 

 white cotton line as a standard of reference. By this method 

 copper oleate easily led all the materials tested as an all-round 

 preservative in salt water. 



PRELIMINARY EXPERIMENTS. 



In a paper by J. T. Cunningham (1902) mention was made of the 

 successive use of soap and copper sulphate, by which lines were 

 colored a blue green, a method used by French sardine fishermen. 

 This method, which deposits a comparatively insoluble form of 

 copper in the lines, appeared to deserve more attention than it had 

 yet received. C(jpper is well known to be an exceedingly toxic 

 substance to lower plant life, bacteria, algaB, etc., and higlily antago- 

 nistic to certain ferments, although comparatively harmless to the 

 higher animals, and therefore seemed a good prospect for trial in 

 different forms. The ferrocyanide of copper is highly insoluble, 

 impermeable to water when dried, and can be applied without 

 difficulty by wetting the lines successively with solutions of copper 

 sulphate and potassium ferrocyanide. Accordingly, in 1920 a small 

 preliminary series of exposures and tests was carried out that 

 included these two treatments — copper soap and copper ferrocyanide. 

 For comparison and control untreated lines were used, and also the 



