PRESERVATION OP FISH NETS 



433 



MATERIALS TESTED 



For this series of tests only cotton twine similar to that used 

 throughout the other tests was used. The preservatives tested 

 were copper oleate (EE), the copper oleate-boiled linseed oil com- 

 bination (GG), rare-earths treatment (RE), and the rare earths 

 and copper oleate (RC). The untreated line (A) was used as a 

 control. Two sets of six lines each were treated with the preservatives 

 mentioned. One of these sets was to remain in water continuously 

 from May 25, 1923, to November 25, 1923, a sample being removed 

 at the end of each 30 days and tested for tensile strength. The other 

 set was removed at the end of each 30 days, washed, dried, treated 

 with copper oleate, and again placed in the water, a sample line 

 being kept out each month for measurement of tensile strength. 



45 



40 



35 



z 30 



o 25 



P 20 



^ 15 



10 



5 w 



2 3 4 5 



NUMBER OF MONTHS EXPOSED 

 TREATED ONCE EVERY 30 DAYS 



TREATED ONLYATBEGINNINfiOFTE5T 



Fig. 17.— Tensile strength of cotton lines exposed in the Potomac River at Washington, D C. 



TENSILE STRENGTH 



The results of the tensile strength measurements are shown 

 graphically in Figure 17. In this graph the broken lines show the 

 samples that were treated only at the beginning of the test, while 

 the heavy lines show the samples treated with copper oleate every 

 30 days. The samples receiving only one treatment of copper oleate 

 showed a sharp decline in tensile strength after the third month 

 and were completely rotten at the end of the fourth month. The 

 samples treated every 30 days (represented in the graph by heavy 

 lines) were as strong at the end of six months' exposure as at the 

 beginning of the test. 



