PRESERVATION OF FISH NETS 



435 



copper oleate, tar, and the copper oleate-tar mixture showed a shght 

 increase in length after treatment. This was probably due to the 

 decrease in resistance of the fibers against each other, caused by the 

 lubricating effect of the preservatives. The quercitron-ammoniacal 

 copper sulphate caused a very appreciable amount of shrinkage on 

 hemp. 



EFFECT OF EXPOSURE TO SUNLIGHT 



Attention should be directed to effects of exposure of nets to sun- 

 light. It is common practice for fishermen, whenever opportunity 

 oners, to wash their nets and lay them out on the sand or grass to dry. 

 This practice may have a marked effect on nets, either untreated or 

 treated with a preservative. 



Fig. 19. — Shrinkage of lines, caused by one api)lic-ation of preservative 



Waentig (1923) showed that cotton fibers of 7.2 grams tensile 

 ■strength before illumination were reduced to 3 grams by direct illu- 

 mination wdth mercury vapor arc ultra-violet light for 24 hours. 

 Sunlight is known to contain a considerable proportion of these rays. 



DePuyster (1923) points out that in the presence of air cotton 

 hbers are j^ellowed and weakened by exposure to sunlight. He also 

 shows that the presence of salts of copper and iron accelerate this 

 deteriorating action of light. Tliis is an important consideration 

 where copper oleate is concerned. Taken together, with the fact 

 that copper oleate appears to be decomposed by sunhght, this argues 

 strongly against exposure of nets, especially those treated with copper 

 oleate or bluestone, to sunlight. The nets should be dried in the 

 shade or on cloudy days, if possible. 



Holman and Jarrell (1923) show that cotton twine suffers deteri- 

 oration on exposure to the weather under a great variety of protecting 



