24 



U. S. BUREAU OF FISHERIES. 



bility, witli about 40 oscillations; copper paint, which made such a 

 good showing in the tensile-strength tests, is here at a great disad- 

 vantage, the lines being stiff or wiry and making only abojat 30 

 oscillations under the conch tions described; finally, the tars, petro- 

 leum products, and gilsonite cause the greatest stiffening, the lines 

 treated with them making only about 20 oscillations. 



According to these tests, if we express the flexibility of tarred 

 lines as 1, then the other preservatives have approximately the fol- 

 lowing flexibility values: 



Petroleum product 1 



Gilsonite 1 



Copper paints IJ 



Tanning methods 2 



Copper oleate 3 



RESISTANCE TO MECHANICAL WEAR OR ABRASION (WEARING QUALITY). 



In experiments so far presented and discussed, the undesirable 

 changes in the lines were brought about during exposure principally 



f^ 



A^' 



Fig. 13.— Apparatus used for testing the wearing quality of lines. 



by decomposition or weakening of the lines, presumably by chemical 

 or biological agencies. These agencies are, perhaps, not always the 

 greatest enemy of lines. It has been shown that m air and exposed 

 to the weather cotton lines do not undergo rapid deterioration. 

 Many types of nets are actually in the water only a small part of the 

 time. They are handled much, however, are dragged over the gun- 

 wales of boats and across decks and wharves, and the lines rub against 

 themselves during such handling. No doubt this factor of mechan- 

 ical wear or abrasion is highly important in such gear as purse seines, 

 haul or drag seines, and trawls. It is to be expected, also, that the 



Ereservatives used will have an important bearing on this factor, 

 like flexibility, it has often been recognized qualitatively as a factor, 

 but has never been given quantitative measurement or expression. 

 In the present work the attempt was made to measure the wearing 

 quahty of the lines treated. 



