FISHERY INDUSTRIES OF THE UNITED STATES, 1923 145 



quick to see the possibilities and sufRcient quantities of copper oleate 

 were produced to meet the demand. Its use as a fish-net preservative 

 has even passed beyond the borders of our own country. The results, 

 on the whole, give very favorable evidence of the usefulness of copper 

 oleate. but for certain fishing gear modifications of application have 

 been found to be necessary. 



Further experiments were conducted on the preservation of fish 

 nets, and a large series of tests were made. This series included tests 

 in salt water at Beaufort, N. C; Boothbay Harbor, Me.; San 

 Pedro, Calif; and Astoria, Oreg. ; and in fresh water at Charlevoix, 

 Mich.; Put in Bay, Ohio; Fairport, Iowa; and Washington, D. C. 

 Previous tests had indicated that copper oleate was possibly slightly 

 too soluble (especially in fresh water) to be entirely satisfactory as a 

 preservative. In an effort to overcome this objection copper oleate 

 was applied in combinations including both raw and boiled linseed 

 oil, paraffin, and coal tar. It was found, however, that although 

 linseed oil decreased the solubility to some extent, this combination 

 does not make as efficient a preservative and anti-fouling agent as 

 copper oleate alone. Evidently a certain degree of solubility is 

 desirable. Tests in the Potomac River demonstrated that it is well 

 to frequently treat with copper oleate twine that is continuously 

 exposed, and it was found that twine treated every 30 days lasted 

 almost twice as long as that given but one treatment. 



The experiments as a whole clearly indicated that the use of coal 

 tar with copper oleate preserved the tensile strength of the lines best. 

 Where considerable increase in weight and stiffness is objectionable, 

 such treatment, of course, should not be given. 



Other experiments showed that, in general, twine that is periodi- 

 cally submerged will last longer than that continuously submerged. 

 It was also found that there was a marked difference in effectiveness 

 of preservatives in one year as compared with their effectiveness 

 when similarly used in the same waters the following year. It is 

 therefore clearly indicated that the degree of success to be attained 

 with any net preservative in any particular case can not be predicted. 

 It can, however, be said, when all factors are taken into consideration, 

 that copper oleate has proved itself superior to any preservative 

 tested experimentally. 



IODINE CONTENT OF SEA FOODS 



In recent years a lack of iodine in food and drinking water has 

 been recognized as one of the most important causes of endemic 

 goiter, cretinism, and other disorders of the thyroid gland. Thyroxin, 

 the active principle of the thyroid gland, has been shown to be an 

 iodine compound. Various observers have shown that it is only 

 necessary to have small amounts of iodine in the food or drinking 

 water to enable the thyroid gland to function properly. 



Physiologists and physicians recently have called attention to the 

 probability that sea foods might constitute an agreeable and con- 

 venient source of iodine for the pubUc at large. In order to supply 

 information on this subject, an investigation of the iodine content 

 of sea foods was made in the fishery products laboratory, and the 

 iodine content of a large number oi fresh and salt water fish and 

 shellfish was determined. The work showed that oysters, clams, 



