FISHERY INDUSTRIES OF THE UNITED STATES, 1932 157 



shown by tlie haddock-liver oils when tested both biologically and 

 coloriinetrically. 



Tests with the colorimetric method of determining vitamin A, 

 when compared to biological results on the same oils indicate tliat this 

 rapid method offers a vahiable aid to liver oil manufacturers for keep- 

 ing a rough control on the vitamin A value of the various lots of oil 

 prepared. 



NET PRESERVATION 



The testing of preservatives for heavy nets was continued during 

 1932 by W. T. Conn, technologist of the Division, to twines used in 

 lake and river waters in addition to those used in salt and brackish 

 waters. From tests extending over a period of three years a principle 

 of preservation has been established which has proved efficacious for 

 this type of net even when subjected to exposure in water for long 

 periods. In its simplified form this principle consists of giving the 

 twine a series of treatments which in some way apparently effect a 

 chemical change in its composition and then giving it a cover treat- 

 ment. The first series of treatments consists of degumming or cleans- 

 ing the twine from natural resins and from oil added to it in the mill, 

 then a chemical treatment which subjects the degummed twine to a 

 toxic dyeing, followed hj a fixing treatment and then thorough wash- 

 ing in clean water. For the final, or cover, treatment, the twine is 

 coated with tar. In this connection no tar has been found which is 

 superior to the specification tar previously recommended by this 

 Bureau, although a liigh acid tar has been found beneficial. 



Twines prepared as above have shown great resistance to depre- 

 ciation in every locality wliere exposures were made during the past 

 3 years. 



Research on net preservation also has shown that mercury, in 

 organic combination, mixed with the tar is highly efficacious in killing 

 marine weeds as well as acting as a preservative agent. 



The beneficial use of antioxidants in connection with preservatives 

 for twine has been confirmed. A very powerful antioxidant has been 

 found which when mixed in very small proportions in tar acts as a 

 preservative for both the tar and the twine. 



It is apparent that the preservation of most seines and light nets is 

 dependent upon proper cleansing and storage. In line with this, the 

 Bureau has advocated the washing of gill nets with lime water. 

 Where this recommendation was followed in 1932 it was observed 

 that the life of the nets was trebled, especially when the}' were 

 washed immediately after the fish were removed. Further study 

 of the drying and storage of fishing nets in the shade has confirmed 

 previous recommendations for this practice. 



In cooperation with the Bureau of Construction and Repair, Navy 

 Department, an extensive investigation of the preservation of manila 

 rope has been carried on through the year and will extend into 1933. 

 As a result of this work it is expected that formulae will be developed 

 for the preservation of ropes under all conditions. 



In the course of this investigation principles of preservation have 

 been developed that may be of considerable value when applied to 

 other textile material such as sails, awnings, thread, etc. 



