PRESEKVATION OF FISH NETS 429 



flexibility tests throughout the entire period of exposure, they were 

 omitted in 1923 on all series except the one exposed at Fairport, 

 Iowa. The results of these measurements are shown graphically in 

 Figure 12. 



It will be noted that the twine used during the 1922 season was 

 somewhat less flexible than that used in the present work. The cop- 

 per oleates caused a slight decrease of flexibility immediately after 

 treatment, which may have been due to the use of a slightly harder 

 material caused by differences in manufacture. At the end of the 

 first month, however, the flexibility showed a marked increase, and it 

 wiU be remembered that the tensile strength decreased rapidly during 

 this same period. Coal tar (KK) caused an immediate decrease in 

 flexibility, which decrease became gradually greater until the end 

 of the second month, when it began to increase. During the same 

 period the tensile strength remained about constant. However, at 

 the end of the second month a sharp decrease occurred, with a corre- 

 sponding increase in flexibility. The proprietary wood preservative 

 (LL) and azulmic acid (MM) caused an immediate increase in the 

 flexibility while all others caused a decrease. 



Resistance to mechanical wear or abrasion (wearing quality). — Tests 

 of the wearing quality of cotton lines were also made on the test 

 lines at Fairport, Iowa. This work was done by the method de- 

 scribed in our previous report. These results are shown graphically 

 in Figure 13. On the unexposed samples the copper oleates (GG 

 and HH) lead in eflectiveness. Coal tar (KK) and the copper 

 oleates (FF and EE) follow in the order named. At the end of one 

 month's exposure, however, coal tar was easily first in resisting 

 mechanical wear and continued so throughout the test. Samples 

 that had been exposed for three months still withstood some 8 or 10 

 strokes on the test apparatus. Of the remaining sample lines, 

 those treated with copper oleate were in the best condition after 

 one month's exposure, withstanding several strokes on the tester, 

 whereas lines treated with other preservatives were completely 

 rotten and showed no wearing resistance whatever at the end of one 

 month. 



TESTS WITH MANILA HEMP LINES 



Materials tested. — The preservatives and preservative methods 

 tested on hemp were copper oleate in four variations (NN, 00, PP, 

 and QQ), the quercitron-ammoniacal copper sulphate method (WW), 

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

 treated control line (I)D). 



Tensile stren^gtJi. — The results of tensile-strength measurements 

 on manila hemp samples are shown graphically in Figure 14. None of 

 the sample lines lasted for the full six-month period of exposure. Coal 

 tar (XX) and the copper oleate-coal tar mixture were about equal 

 in their effects, samples treated with these materials lasting for five 

 months. Lines treated with the copper oleates (SS, TT, UU, and 

 VV) come next, these samples lasting for three months. The samples 

 treated by the quercitron-ammoniacal sulphate method (WW) lasted 

 but two months, while the -untreated sample (DD) was completely 

 rotten in less than two months. 



