36 American Fisheries Society. 



cially studies directed toward the development of new preserva- 

 tives, and toward the definite elimination of those which can be 

 shown to have little or no value. 



Accordingly, after the review of literature above referred to 

 was completed, an investigation of net preservatives was under- 

 taken in the summer of 1930 ; this investigation has been pursued 

 and is still being pursued on an increasingly extensive scale, so that 

 thousands of tests have been made of many preservatives on both 

 cotton and linen thread, in salt water in various latitudes, at dif- 

 ferenj- temperatures, and in fresh water of the Great Lakes. This 

 paper will report, in somewhat abridged form, the more important 

 resvlts of the work, but for lack of space will be limited to the 

 wovk of cotton lines. What was perhaps the greatest obstacle to 

 rrpid progress was the lack of reliable technique of testing the 

 ramples before and after exposure, a lack which is not only evident 

 on examination of the literature, but also borne out in private cor- 

 respondence with the Director of the Dutch Laboratory at Utrecht, 

 Dr. J. Olie, who states that technique of testing is the greatest need. 

 Accordingly, much attention has been given to this important as- 

 pect of the subject, and instruments for and methods of testing 

 have been devised, tried, improved and adopted. 



PRELIMINARY EXPERIMENTS. 



By way of a beginning, a small series of lines was tested in 

 1920. The thread used was No. 24 white cotton cord. The treat- 

 ments were (1) Bull's method, quercitron, mordanted with potas- 

 sium bichromate and copper sulphate; (2) impregnation of lines 

 with copper ferrocyanide by treatment with approximately N/10 

 copper sulphate, followed by potassium ferrocyanide; (3) same as 

 (2) but potassium ferrocyanide was applied first; (4) same as (2) 

 but N/2 solutions were used instead of N/10; (5) solution of 

 Ivory soap followed by solution of copper sulphate, both solutions 

 at Y5° C, when applied; and (6) white lines, no treatment. No. 

 5 is a method used by French sardine fishermen, and since it de- 

 posits an insoluble copper soap on the lines, appeared to deserve 

 more study than it had hitherto received. Two examples were 

 prepared by each method, and were placed in sea water at Beau- 

 fort, N. C. One sample of each was removed at the end of four 

 weeks, the other ten weeks. The breaking strength was ascertained 

 with the following results : 



