30 



U. S. BUREAU OF FISHERIES. 



No. Rows per yard. 



10. Green oil alone 25^ 



11. Cutch and Stockholm tar 27 



12. Cutch, Stockholm tar, and 



green oil 254 



13. Cutch and linseed oil 27 



14. Soap and copper sulphate 27 



15. Soap, copper sulphate, and lin- 



seed oil 27 



No. Rows pp r yard. 



1. Cutch only 26-i 



2. Glue and cutch 25i 



8. Cutch, glue, and bichromate- 25^ 



4. Cutch and copper sulphate 254 



5. Coal tar and cutch 28| 



'6. Cutch and coal tar mixed 27 



7. Cutch. tar, and green oil 25^ 



8. Coal tar and gi-een oil 25^ 



9. Cutch and green oil 26j 



All the methods caused shrinkage, the greatest being caused by 

 coal tar and cutch, but the other combinations of cutch and tar 

 caused marked shrinkage. All the tanning methods cause shrinkage, 

 and the shrinkage increases with each application of the preserva- 

 tive. 



To conclude the discussion of tar as a preservative, it can be said 

 that tar effects excellent preservation, is comparatively inexpensive, 

 and requires much less labor and time than, for example, the com- 

 bination of catechu and linseed oil. For the heavier and coarser 

 kinds of nets that are anchored or moored in the water, such as tram- 

 mel or pound nets or nets that are handled by machinery, the method 

 is well suited. But for gill nets, the method is not at all suited, and 

 for even the heavier seines that are hauled by hand, consideration 

 should be given to the extra weight added by tar and the conse- 

 quently increased number of men necessary to handle nets so pre- 

 served. In such cases, especially for nets that can be dried occa- 

 sionally, the more improved barking methods, such as quercitron and 

 potassium bichromate, are likely to prove to be better and to be little 

 more expensive or laborious than methods employing tar. 



Tar should never be mixed with catechu solution or anything else 

 containing water before application to the net and should never be 

 applied to a wet net. It may be thinned with creosote, " green oil," 

 turpentine, etc., without injury. If a net be cutched or barked before 

 being tarred, it should be thoroughly dried before the tar is applied. 

 While tar may be applied profitably to new, white nets, it seems 

 likely that it will always yield a good return on the investment to 

 tan the nets with quercitron and bichromate and to follow with a 

 thorough drying before application of the tar. 



CREOSOTE, SMOKE, ETC. 



As stated above, tar consists of a solid and a liquid part. The 

 liquid part really consists of a number of different liquids and vola- 

 tile solids, such as carbolic acid, benzol (or benzene), napthalene, etc., 

 mixed, which, when separated, have different important commercial 

 uses. They are distilled off from coal tar. One portion (the third 

 main portion distilling over at from 230 or 240 to 270° C.) is known 

 as " green oil " or creosote oil, a greenish-yellow, oily liquid, heavier 

 than water, and containing various antiseptic substances. It is used 

 for the preservation of crossties, fence posts, telegraph and tele- 

 phone poles, and has been used for the treatment of nets. Reference 

 to Cunningham's table above shows that creosote oil alone is a good 

 preservative for nets and causes little shrinkage; it also possesses 

 this advantage, that it does not make nets stiff. Tlie principal objec- 

 tion to its general use is that it washes out or evaporates rather rap- 



