FISH-ISTET PRESERVATIVES. 63 



mixture and hung (not piled) to dry. Any unused portion of the 

 copper oleate in gasoHne may be kept indefinitely in a tightly corked 

 can, such as a 10-gallon oil can. For larger quantities a steel gasoline 

 barrel is suitable. The treatment may be repeated as often as seems 

 desirable without danger of injury to the twine. 



GRADING THE SEVERAL MATERIALS AS ALL-ROUND PRESERVATIVES. 



In the experimental part of this paper it has been shown that the 

 several materials studied differ in value as net preservatives— in one 

 particular respect one preservative may excel, in another some other 

 preservative. The impression may have been given that in most 

 respects copper oleate is best. But, just how much better is one 

 preservative than another, considered generally? Some systematic 

 and impartial method of attacliing values to the different factors — 

 such as tensile strength, stiffness, and wearing quality — by which to 

 grade the several preservatives accordingly is desirable. Can we 

 not derive a figure that is made up of the several values of tensile 

 strength, wearing quality, flexibility, etc., that will give an indication 

 of the all-round value of each preservative? 



In deriving such a figure it is impossible to avoid making assump- 

 tions that are more or less arbitrary. It is also necessary to ignore the 

 obvious fact that for different purposes and classes of nets the relative 

 weights of the different factors are quite dissimilar. For example, 

 in gill nets the necessity of flexibility absolutely dominates the 

 choice of material and preservation, while in pound nets flexibility 

 is of no great importance, but preservation of tensile strength, ability 

 to withstand chafing or abrasion, and resistance to fouling by marine 

 growths are decisive factors. 



In selecting a suitable preservative, therefore, one can not avoid a 

 consideration of the relative importance of the several factors for the 

 particular purpose the net is intended to serve. Nevertheless, our 

 new preservative, copper oleate, is proposed for all classes of nets. 

 If it can make a good score in all or most of the several require- 

 ments that make it suitable for many different purposes, it is more 

 desirable than a preservative that excels for some limited purpose 

 and is useless for others. 



The following method of grading the preservatives for all-round 

 uee on cotton lines involves the minimum number of arbitrary assump- 

 tions : (1) The breaking length of the treated line was first calculated; 

 that is, the length of line that ^vill just hold itself up. (2) This 

 figure was then reduced to the same extent as the shrinkage was 

 found to reduce the length of cotton lines on application of the 

 preservative. (3) This figure was then multiplied by a factor that, 

 in the case of white untreated line, brings the breaking length to 100. 

 Thus, the samples were compared with white line as a standard of 

 excellence. (4) The munber of strokes on the wearing tester was 

 multiplied by a factor that, in the case of white untreated line, 

 brings the number of strokes to 100. Here, again, the samples 

 were referred to white line as a standard. (5) The number of 

 pendulum oscillations of the several samples (flexibility) was multi- 

 plied by a factor that, in the case of white untreated line, gives 100 

 oscillations. This factor is also referred to white line as a standard. 

 We thus take into the reckoning tensile strength, increase in weight, 



36199°— 23 5 



