6 



U. S, BUREAU OF FISHERIES. 



method found in the literature to be best. This latter method, 

 described by Bull (1902) and reviewed by Taylor (1921, p. 22), con- 

 sists of treating the lines first with a hot solution of quercitron in 

 water, then with a cold solution of potassium bichromate and copper 

 sulphate. 



The lines prepared for exposure were treated as follows: (1) Lines 

 treated by Bull's method (quercitron, potassium bichromate, and 

 copper sulphate); (2) a tenth normal solution of copper sulphate 

 followed by a tenth normal solution of potassium lerrocyanide; 

 (3) a tenth normal solution of potassium ferrocyanide followed by a 

 tenth normal solution of copper sulphate; (4) same as (2), but half 

 normal solutions instead of tenth normal solutions were used; (5) a 

 hot solution of soap followed by a hot solution of copper sulphate. 



Samples of No. 24 white cable-laid, hard-finish cotton lines were 

 prepared, two by each method, and sent to Beaufort, N. C, for 

 immersion in sea water in June. One sample of each was removed 

 and tested after 4 weeks, the other after 10 weeks. Table 2 shows 

 the tensile strength in kilograms. 



Table 2. — Tensile strength of cotton lines exposed in sea water at Beaufort, N. C, 1920. 



Number and method of treatment. 



1. Bull's method (quercitron, etc.) 



2. Tenth normal copper sulphate and tenth normal potassium ferrocyanide 



3. Tenth normal potassium ferrocyanide and tenth normal copper sulphate. 



4. Half normal copper sulphate and potassium ferrocyanide 



5. Soap and copper sulphate 



6. Untreated, control (tensile strength before exposure, 18 kg.) 



Tensile strength 

 after— 



4 weeks. 10 weeks. 



Kilograms. 

 13.40 

 10.86 

 10.02 

 13.06 

 11.96 

 10.48 



Kilograms. 

 7.78 

 3.66 

 3.22 

 4.98 

 7.32 

 1.18 



Bull's method was best. Copper ferrocyanide was a failure, for the 

 reason, obvious on examination, that all the copper ferrocyanide was 

 deposited near the surface of the line; the inner parts were not 

 reached. The copper soap preserved nearly as well as Bull's method, 

 though examination revealed the soap to be confined largely to the 

 exterior of the line, and the copper soap itself was a precipitate not 

 uniformly spread over the fibers. 



CONCLUSIONS FROM PRELIMINARY EXPERIMENTS. 



None of the methods included can be regarded as satisfactory, as 

 a marked decomposition occurs in all of them on 10 weeks' ex- 

 posure. 



Copper ferrocyanide is of little value. 



Copper soap promises well and calls for more study to effect good 

 penetration and uniform distribution. 



COPPER SOAP. 



The green precipitate deposited on the lines by successive applica- 

 tions of soap and bluestone is, of course, copper soap, a mixture of 

 several fatty acid salts of copper oleate, stearate, palmitate, etc. 

 The two principal defects in tliis mode of application are (1) the 



