FISH-NET PRESERVATIVES. 



11 



Table 3. — Tensile strength of cotton lines exposed on roof of Fishery Products Labora- 

 tory, Washington, D. C, 1922. 



Symbol and treatment. 



A— Whit line, untreated control 



B — Copper oleate 7 per cent in gasoline 



C — Copper oleate 7 per cent in gasoline, 5 per cent oil, 1-1000 



cresol 



D— Copper oleate 1 1 per cent in gasoline 



E — Copper oleate 11 per cent in gasoUne, 2 per cent oil 



F — Coal tar 50 per cent, benzol 50 per cent 



G — Pine tar 50 per cent, benzol 50 per cent 



H — Coal tar 25 per cent, pine tar 25 per cent, benzol 50 per 



cent 



I — Quercitron and potassium bichromate 



J — Petroleum product'No. 1 



K — Proprietary waterproofing material 



If— Dutch method 



Unex- 

 posed 



Number of months exposed. 



Tensile strength in pounds. 



28.0 

 29.6 



28.2 

 31.1 

 28.4 

 44.0 

 44.0 



46.0 

 32.4 

 46.0 

 41.0 

 33.0 



1 Average of 60 breaks; every other figure in this table is the average of 15 breaks. 

 ' No sample run. 



Here, it will be observed, the lines preserved by any of the materials 

 suffer an immediate diminution of strength even before they are 

 exposed. (K, the conmiercial waterproofing was not tested im- 

 mediately after treatment.) The reason for this diminution of 

 strength appears to be the lubrication of the fibers. The cotton 

 line used consists of comparatively short fibers that are made to 

 serve the purpose of a long line by being twisted together. The 

 friction between the fibers holds them together. When a pull breaks 

 the line, some of the fibers are actually broken, others disengaged. 

 The introduction of a foreign substance between these fibers or 

 strands may greatly alter the behavior of the line. A lubricant, by 

 diminishing the friction between the fibers, causes more of them to 

 slip out or become disengaged and fewer to break; consequently, the 

 line is weakened. We see that most of our preservatives immedi- 

 ately after application cause such a weakening. These remarks may 

 not, and probably do not, apply to lines made of very long fiber cotton, 

 like sea-island cotton. The tensile strength of such lines is probably 

 the sum of the tensile strengths of the fibers, and binders would have 

 little effect on the tensile strength. 



On the other hand, anything between the fibers that increases the 

 friction or glues the fibers together will cause an increase in strength. 

 This effect becomes evident after the material begins to become 

 sticky or dry. In the present instance the lines treated with copper 

 oleate, B, C, D, and E, and by the tanning methods, I and L, on 

 exposure to the weather suffer a gradual though small diminution 

 of strength. At the end of six months' exposure to weather the 

 lines are still strong and useful. These preservatives have no body 

 or binder. The other preservatives that have a body or binder — 

 namely, coal tar, F; pine tar, G; a mixture of the two, H; and the • 

 petroleum product No. 1, J — show an increase in strength as the pre- 

 servative dries. This increase is sufficient to neutralize any deterio- 

 ration of the fibers. Those preservatives that behave in a similar 



