58 U. S. BUBEAU OF TISHERIES. 



In salt water the Dutch method proved itself to be a very good pre- 

 servative, but not the best. Lines preserved by it are strong, light, 

 flexible, but wear easily from mechanical abrasion and shrmk con- 

 siderably, and the method is somewhat troublesome of application. 

 Smce the quercitron and potassium bichromate method and the 

 Dutch method are similar, except for the absence of copper from 

 the one and the presence of it m the other, it is clear that the pre- 

 serving effect of the Dutch method lies in the copper and not in the 

 tanning. 



COPPER PAINT. 



This material, long used for the bottoms of boats and ships to 

 prevent the entrance of marine borers and to prevent also the attach- 

 ment of fouling by barnacles and other growtlis, has been introduced 

 only recently as a preservative of lish nets. The two commercial 

 samples tested in these experiments are regularly sold for the purpose. 

 One (Q) is a product prepared for fish nets by a considerable thinning. 

 It contains much less copper oxide than the ship's paint. Accordmgly, 

 its properties that depend on body — that is, stiffness and weight — are 

 somewhat less extreme than those of the straight ship's paint (11), 

 the other sample tested. This latter contains very much more 

 copper. It stiffens lines and increases their weight more than the 

 other copper paint. The copper oxide present gives to lines treated 

 by either of these paints a harshness that greatly reduces the wearmg 

 quality of lines treated by it. It is in this particular that they are at 

 a great disadvantage when compared with other preservatives. They 

 cause very little shrmkage but increase the weight from 60 per cent 

 (Q) to 125 per cent (R). They both impart to nets the familiar 

 reddish or coppery color that is seen on ships' bottoms pamted with 

 them. They are expensive but are not very troublesome to apply, 

 as the nets are to be put into service in water without waitmg to dry. 



Both copper paints proved themselves to be most excellent pre- 

 servatives oi tensile strength under all conditions tested, both m salt 

 and fresh water, being usually the strongest lines of all after exposure. 

 They add something to the tensile strength of unexposed lines, but 

 this increase is not sufficient to compensate for the added weight, as 

 shown by the breakmg length data. R, contammg as it does a larger 

 proportion of copper, is more effective under very severe conditions 

 than Q, which contains less copper. When compared with the lines 

 treated with copper oleate, which contained very much less copper, 

 it appears that the large deposits of copper in the pamts are unneces- 

 sary. Copper paints entu-ely prevented f oulmg iu all the experiments. 



In summary, copper paint is an excellent preservative of tensile 

 strength and in preventmg fouling, but is seriously lacking in wearing 

 quality. It stiffens the lines and increases their weight and is de- 

 cidedly expensive. It is unsuitable for gill nets and light seines. 



PETROLEUM PRODUCTS. 



These two materials, J and X, submitted for test, are prepared from 

 petroleum from the Western States. They are black tarry liquids, J 

 being heavier than X. X was prepared thin so as to be suitable for 

 gill nets. They impart to the line a brown color, penetrate well, and 

 as far as appearances go might readily be taken as good substitutes for 



