NET PEESEKVATIVE TREATMENTS 45 



After the tars are dissolved in the kerosene the sludge is allowed 

 to settle for 24 hours. The clear liquid is then poured off and mixed 

 with the G pounds of fine red oxide of copper. The red oxide of 

 copper should be " Navy standard," that is, containing not less than 

 88 per cent cuprous oxide and fine enough so that 98 per cent can be 

 sieved through a 350-mesh screen. When the net is dipped in this 

 mixture it is essential that the mixture be constantly agitated. To do 

 this it has been found good practice to operate a bilge pump in 

 the center of the kettle or tank, in order to draw the mixture from 

 the bottom of the tank and distribute it over the section of the net 

 being treated. 



Another method of preserving gill nets, which is common practice 

 in certain localities, is to wash them in a weak solution of copper 

 sulphate (bluestone). This chemical, while it doubtless acts as a 

 deterrent to bacterial development, can not be regarded as having 

 a very prolonged effect. 



TREATMENTS FOR PURSE SEINES 



Most purse seines on the Pacific coast of the United States are 

 preserved by tanning. During the fishing season it is the general 

 practice of the fishermen to wash the seines and then dip them in a 

 solution of hemlock extract about once each week. These purse 

 seines are hand knit by the fishermen from twine which has been 

 tanned prior to purchase. On the Atlantic coast of the United States 

 purse seines are generally preserved with light crude coal tar. The 

 deterioration of purse seines, aside from mechanical wear, appears 

 to be due to the breakdown of the twine by heating, caused by the 

 action of bacteria in the slime which clings to the webbing after a 

 haul has been made. Damage from this cause may be lessened by 

 washing the net thoroughly with sea water after each haul and then 

 sprinkling the net with salt at the end of each day's fishing. While 

 in storage, purse seines should be packed in enough salt to cover all 

 parts of the webbing. 



BIBLIOGRAPHY 



The reader may be interested in the following publications of the 

 Bureau of Fisheries on the subject of net preservation, which may be 

 purchased from the Superintendent of Documents, Government 

 Printing Office, Washington, D. C, at the prices stated: 



Taylor. Harden F. 



1921. Preservation of fish nets. Appendix IV, Report, U. S. Cjommissioner 

 of Fisheries for 1920 (1921). Bureau of Fisheries Document No. 

 898, 35 pp., 1 fig. Washington. 10 cents. 

 Taylor. Harden F., and Arthur AV. Wei.ls. 



1923. Properties and values of certain fish-net preservatives. Appendix I, 

 Report, U. S. Commissioner of Fisheries for 1923 (1924). Bureau 

 of Fisheries Docuinent No. 947, 69 pp., 35 figs. Washington. 15 

 cents. 

 1926. Further experiments on the preservation of fish nets. Appendix VII. 

 Report, U. S. Commissioner of Fisheries for 1925 (1926), pp. 409- 

 437. Bureau of Fisheries Document No. 998, 29 pp., 19 figs. 

 Washington. 10 cents. 



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