56 U. S. BUREAU OF "FISHERIES. 



COAL TAR. 



The coal tar used was the 270° F. fraction, a thick, black, sirupy 

 liquid. It contains many things, including creosote or the cresols, 

 that are highly antimicrobic. Under conditions of exposure to 

 weather it protects the lines well. At Key West, in sea water, it 

 showed a good preserving effect on tensile strength. At Beaufort 

 it held the lines in good condition for about two months, after which 

 time a rapid deterioration took place. This, it is assumed, is ac- 

 counted for by the fact that the creosote present at first preserves the 

 lines, but when it has dissolved, the lines are no longer protected. 

 In ability to resist mechanical wear coal tar is at first very good, but 

 as the lines stiffen and weaken on exposiu-e this quality rapidly 

 disappears. Tar greatly stiffens the lines. Where an untreated 

 cotton line swings 40 to 50 times, a tarred line swings only about 

 15 to 20 times. Tar also increases the weight of lines, under con- 

 ditions of application herein described, to the extent of about 50 to 70 

 per cent. 



There is a noticeable increase in strength in tarred lines over the 

 white lines, to which it is applied. This increase in strength, caused 

 by a cementmg of the fibers, is not sufficient to compensate for the 

 increase in weight. The breaking length of an unexposed tarred 

 fine is less than that of the white line. 



In resistance to the accumulation of foulmg by marine growth 

 tar is poor, and the tiine required to dry the applied tar is 12 hours 

 or more. Tar is cheap in material but is laborious and messy to apply. 

 It colors the nets dark brown or black. 



Coal tar is suitable as a preservative for heavy nets, and when 

 applied in concentration is much better than nothing on two months' 

 continuous exposure, after which it is comparatively worthless. 

 Fortified with copper oleate, coal tar was an extraordinarily good 

 preservative. This will be referred to later. 



PINE TAR. 



Pine tar behaves very much like coal tar, running a close second 

 to it in most respects. It does not preserve tensile strength quite 

 so well, but, on the other hand, is not quite so stiffening. Little can 

 be said in favor of pine tar as against coal tar. 



MIXED TAR. 



The tars mixed were also similar to the straight tars, the properties 

 of the mixture being usually intermediate between those of the 

 separate components. 



TANNING OR BARKING. 



Next to tarring barking is the commonest preservative treatment 

 applied in this comitry. The use of bark is principally confined to 

 gear that can not be tarred, such as giU nets and light seines. The 

 barking process usually consists of dipping the net in a hot decoction 

 of oak bark, cutch, or other tanning extract, in water. Since, in a 

 previous paper (Taylor, 1921) it was shown that barkmg alone is of 

 no noticeable value as a preservative (though the gear may be well 



