PRESERVATION OF FISH NETS 423 



this material showed a considerable depreciation of tensile strength 

 at the end of two months and continued to lose throughout the period 

 of test. The quercitron-ammoniacal copper sulphate treatment 

 caused an immediate weakening of the manila fiber, and the lines 

 deteriorated even more rapidly uian the untreated samples. 



SUMMARY OF RESULTS AT PUT IN BAY, OHIO 



1. Cotton lines treated with copper oleate were preserved much 

 more satisfactorily than during the previous year, lasting six months 

 with only slight diminution of strength, whereas in 1922 lines similarly 

 treated were completely rotten in five months. 



2. Cotton lines treated by the quercitron-ammoniacal copper 

 sulphate method were completely rotten at the end of five months, 

 whereas in 1922 similar samples remained well preserved for six 

 months. 



3. Copper oleate and the copper oleate-tar mixture proved to be 

 the best preservatives for manila hemp at Put in Bay. 



4. Coal tar did not preserve hemp as satisfactorily at Put in Bay 

 as at most other places. 



5. The quercitron-ammoniacal copper sulphate treatment proved 

 injurious to manila fiber, and lines so treated deteriorated more rapidly 

 than the untreated lines. 



6. The copper oleate-tar combination proved an excellent preserva- 

 tive of tensile strength for both cotton and hemp lines. 



SERIES EXPOSED IN FRESH WATER AT CHARLEVOIX, MICH. 



For the purpose of obtaining further data as to the effect of Great 

 Lakes water on twine a series of test lines identical with those exposed 

 at Put in Bay was exposed in Lake Michigan at the Bureau of Fish- 

 eries' hatchery at Charlevoix, Mich., from June 19 to December 19, 

 1923. 



WATER CONDITIONS AT CHARLEVOIX 



Complete records of temperature conditions of the water at this 

 point are not available, but it is known to vary from a temperature 

 of about 70° F. during the summer months to about 40° F. during the 

 early part of the winter, when these tests were completed. 



TESTS WITH COTTON LINES 



Materials tested. — The preservatives and preservative methods 

 tested on cotton lines were copper oleate in four variations (EE, FF, 

 GG, and HH), the quercitron-ammoniacal copper sulphate treatment 

 (L), a proprietary waterproofing (JJ), coal tar (KK), the copper 

 oleate-coal tar combination (Y), and an untreated control line (A), 



Tensile strength. — The results of tensile-strength measurements of 

 these lines are shown graphically in Figure 9. The water at Charle- 

 voix does not cause as rapid deterioration of twine as the water of 

 Lake Erie at Put in Bay. At the former location the untreated line 

 still possessed some strength at the end of six months' exposure, 

 whereas at the latter place untreated lines were completely rotten 

 at the end of four months. At Charlevoix samples treated with the 



