PRESERVATION OF FISH NETS 



419 



TESTS WITH MANILA HEMP LINES 



Materials tested. — Besides the tests made with cotton and Hnen 

 Unes, there were also included at Astoria some samples of manila 

 hemp. The twine selected was two-ply manila hemp lobster marlin, 

 such as is used by many lobster fishermen for funnels in lobster pots. 

 The tensile strength of the untreated, unexposed line was 230.8 

 pounds. The preservatives tested on the manila samples were as 

 follows: Copper oleate in four variations (SS, TT, UU, and W), 

 the quercitron-ammoniacal copper sulphate treatment (WW), coal 

 tar (XX), the copper oleate-coal tar mixture (YY), and the un- 

 treated sample (DD). 



55 

 50 

 45 



to 

 Q 40 



Z TV 



35 

 30 



25 



I- 

 «/> 



^ 20 



m 

 z 

 ^ 15 



10 

 5 



X 



I- 

 z 



Ul 



I 2 



NUMdER or MONTHS EXPOSED 



Fig. 5. — Tensile strength of linen lines at 

 Astoria, Greg. 



Tensile strength. — The results of tensile-strength measurements of 

 the individual samples are shown graphically in Figure 6. The 

 effectiveness of the various preservatives used is of the same order 

 on manila as on cotton. The four copper oleates, coal tar, and the 

 copper oleate-coal tar mixture preserved manila over the entire six 

 months of exposure, although in all cases a considerable diminution 

 of strength occurred. The quercitron and ammoniacal copper 

 sulphate treatment (WW) was of no value here as a preservative 

 for manila. This treatment caused an immediate dimunition of 

 tensile strength of 82.7 pounds, or about 35 per cent, and thereafter 

 the tensile strength decreased at about the same rate as in the un- 

 treated material. 



