REPORT OF THE COMMISSIONER OF FISHERIES. 5 



treated for the time required to freeze. The conveyor is located 

 so that it is not exposed to the corrosive action of the brine. Mechan- 

 ical refrigeration is used to refrigerate coils or heat-absorbing 

 units located in the bottom of the apparatus. The salt brine is 

 circulated continuously, only a small volume being required. Trials 

 so far made with this apparatus indicate that it freezes quite satis- 

 factorily, though more extensive trials will yet be necessary. The 

 fish are individually frozen, trim and straight. 



PEESEEVATION OF NETS. 



The bureau's work on the preservation of fish nets has been car- 

 ried to the point of yielding results of value. The several series of 

 samples of twine that had been exposed at several localities in 1922 

 and tested monthly were completed, and the results were prepared 

 I for publication. In addition to numerous well-known preservative 

 materials, there was tried for the first time copper oleate, in which 

 the bureau hoped to discover a better preservative than any of those 

 hitherto used. In so far as experiments of this kind go, the results 

 fully justified expectations. Copper oleate, dissolved in gasoline or 

 other suitable solvent and applied to cotton or linen lines, effected a 

 superior preservation of tensile strength or resisted fouling to a 

 remarkable degree without materially adding weight to the lines or 

 diminishing their flexibility, as so many other preservatives do. The 

 results were very much more satisfactory in salt water than in fresh 

 water. In the latter the copper oleate seems to be somewhat more 

 soluble than in salt water. In a new and larger series of experi- 

 mental exposures of lines begun in the spring of 1923 several other 

 commercial or proprietary preservatives were tested, and an effort 

 also was made to reduce the solubility of copper oleate in water by 

 the addition of linseed oil and paraffin and by other combinations. 

 Success in this direction, if attained, will not only provide a suitable 

 preservative for fresh water but will overcome one of the principal 

 objections to the use of copper oleate in salt water; that is, its 

 tendency to wash out of the lines. 



CANNING SAEDINES. 



In the canning of sardines it is always necessary to remove some 

 of the water from the fish before the cans are finally sealed, else the 

 fish break down to a wet mass and present a poor appearance. In 

 California the usual method of removing the excess water is to pass 

 the fish through a bath of hot oil, wherein much of the water is 

 cooked out. At the bureau's experimental laboratory at San Pedro, 

 Calif., the conclusion has been reached, and heretofore reported, 

 that the oil in which the frying is done becomes oxidized, rancid, 

 and objectionable from a dietetic point of view, since part of it is 

 carried on the fish into the can. During the fiscal year 1923 work 

 has been confined chiefly to the solution of the problem of remov- 

 ing the water by methods other than frying in oil, and considerable 

 progress can be reported. Three methods were tried, all of which 

 showed some merit. They were (a) cooking in strong brine instead 



