PRESERVATION OF FISH NETS 



425 



SUMMARY OF RESULTS AT CHARLEVOIX 



1. Copper oleate, coal tar, and the copper oleate-coal tar mixtures 

 preserved twine for six months' continuous exposure with but shght 

 diminution of strength. 



2. The proprietary waterproofing substance (JJ) did some good 

 as a preservative but did not compare favorably with copper oleate, 

 tar, or the copper oleate-tar mixture. 



3. The quercitron-ammoniacal copper sulphate method did no good 

 whatever on cotton and had a harmful effect upon hemp lines. 



4. The action of the water at Charlevoix is less severe on twine 

 than it is at Put in Bay, Ohio. 



250 

 240 

 220 



3 



200 



180 



160 



140 



120 



100 



80 



60 



40 



20 



12 3 4 5 



NUMBER OF MONTHS EXPOSED 



Fig. 10. — Tensile strength of hemp lines at Charlevoix, Mich. 



SERIES EXPOSED IN FRESH WATER AT FAIRPORT, IOWA 



A series of lines, including cotton, linen, and manila hemp samples, 

 treated with the various preservatives, was exposed in the Mississippi 

 River at the Bureau of Fisheries biological laboratory at Fairport, 

 Iowa, from June 1 to December 1, 1923. On the Fairport samples, 

 in addition to the tensile-strength tests, measurements of the wearing 

 quality and flexibihty were also made. These factors will be discussed 

 in connection with the data concerning them. 



