PRESERVATION OF FISH NETS. 27 



Hut for drift nets tliere are many objections to its use in the manner considered. 

 Tlie net is too ri;j;id and still", and, llu-relore, does not usually mesh the fish 

 well although to somc> extent the net is made more flexible by occasional dips 

 in hot cutdi. which softens tiie tar and removes a portion of it. The rigidity 

 of the net causes it lo wear out mechanically; after two or three years it is 

 apt to give way at the knots, owing to the breaking of the stiffened fibers under 

 the constant bending. 



Another method sometnnes used employs cutch and tar too^ether, 

 the tar beino; stirred into the hot cutch and the net bathed in the 

 mixture. Cunnin<rham found this to be very little better than the 

 cutch or catechu alone, for the reason that the tar does not mix 

 imiformly witli the cutch, but breaks up into little droplets which 

 attach themselves to the threads. The threads are therefore not 

 uniformly protected by the tar. 



Tar consists of two parts, a liquid part which is separately 

 knoAvn as creosote, and a black, solid part which is left behind when 

 the creosote evaporates. When the tar is first applied both are 

 present, but as time passes the liquid creosote gradually evaporates, 

 while the solid part remains. Both assist in protecting the nets, 

 the solid by gluing the fibers together, the liquid by killing bacte- 

 ria ; one i)rotects, the other preserves. 



If in the table given by Bull (p. 20) the samples prepared with 

 tar are compared with samples i)repared in other ways, it is seen 

 that tar holds its own against all rivals, if we consider preserva- 

 tion of breaking strength only. But it is noticed that weight is 

 increased from around l.G grams per 10 meters to around 3.5, 

 or about 2^ times; the breaking length is correspondingly reduced, 

 while the absorption of water is reduced from about 250 per cent 

 to about 50 per cent ; that is, the amount of water the threads will 

 absorb is reduced by the application of tar from about 2^ times its 

 own weight to one-half its own weight. 



The added weight of tar is a very material disadvantage in large 

 nets, for it increases the labor of handling nets and prolongs the 

 time of every moA'e of the net. On the other hand, Bull's table shows 

 that the tarred net soaks up much less water than the barked net 

 and that, since absorbed water adds to the W' eight of the net just 

 as tar does, the weight added by water must also be considered. 



In tlie case of drift nets, where the poise of the net in the water 

 is of greatest im]:)ortance. the balance of the net has a bearing on 

 the method of barking (Jessen, 1906). Jessen argues thus: A 

 quantity of sea water of the same air and salt content and at the 

 same temperature as that of the sea, will neither sink nor float, 

 but will stay at w^hatever depth it is put, and when water thus 

 soaks into a net it will tend neither to sink nor float the net, but 

 is a dead weight. This dead weight, however, must be counter- 

 balanced by a greater weight on the lead line than Avould be needed 

 without it ; that is, the weights on a water-logged net must be greater 

 by an amount equal to the weight of the water in the net in order 

 to keep the net vertical. Thus, if the untreated net in Bull's table 

 took up 227 per cent water (No. 1) and required 24 kilograms 

 stone sinkers, the barked net wdiich took up 179 per cent water 

 (No. 11) would require 21.6 kilograms sinkers, and with the barked 

 and tarred net (Xo. 23) that took up 54 per cent of water, only 

 10.5 kilograms sinkers Avouhl lie needed, and that with lead sinkers 



