REFRIGERATION OF FISH 593 



from metal parts, and this nist may seriously discolor the fish. To 

 the labor necessary for freezing must he added labor for washing and 

 glazing, which, altogether, may be excessive. 



If ice and salt are used as a source of refrigeration, it is impos- 

 sible to maintain uniform temperature and concentration of brine, 

 and refrigeration is wasted by discarding the excess of accumulat- 

 ing cold brine. 



The present writer, while on the technical staff of the Bureau of 

 Fisheries, after study of the theories involved and all the methods 

 proposed for practice, approached the problem by first setting out 

 the requirements that must be met by any entirely satisfactory 

 brine-freezing method and then attempting to design a machine 

 that would meet these requirements. The requirements for an en- 

 tirely satisfactory brine freezer were conceived to be as follows : 



1. Mechanical refrigeration should be used. 



2. The brine should be maintained uniformly as near its cryo- 

 hydric point as possible — that is, as near 6.16° F. below zero, and 

 22.42 per cent, by weight, salt. 



3. To secure uniform operating conditions, operation must be 

 continuous and not by batches. 



4. The maximum rate of heat transfer should be secured by (a) 

 exposing all the surface of the fish to the brine without obstruction, 

 (b) flowing the brine with great rapidity, and (c) avoiding a slug- 

 gishly moving film in immediate contact with the fish. 



5. The fish must be held straight until they become rigid. 



6. Abrasion of fish by rubbing together must be avoided. 



7. The quantity of brine used must be at a minimum and must 

 not be wasted. 



8. The brine must not be contaminated rapidly. 



9. The fish must be washed thoroughly preliminary to freezing, 

 preferably in running water. 



10. The brine must be washed off and the fish glazed. 



11. The machine must be capable of nice adjustment to fishes of 

 different size, speed of freezing, etc. 



12. It should be flexible — that is, applicable to as large a variety 

 of fishes to be frozen as possible. 



13. Metal working parts should avoid contact with corrosive 

 brine, and rusting, in general, must be reduced to a minimum. 



14. Labor for all operations should be at a minimum. 



15. The machine must be suitable and practical for operation on 

 a large scale. 



The approach to the solution of these problems is as follows: 

 1, 2, and 3. If mechanical refrigeration is used, and if operation 

 is continuous — that is, if the fish are fed continuously into the appa- 

 ratus and are continuously withdrawn— maintenance of brine at or 

 near its cryohydric point becomes possible. To secure continuity 

 of operation the fish must be conveyed mechanically through the 

 process from beginning to end. 



4, 5, and 6. If the fish are suspended and sprayed with a violent 

 spray of the brine, we secure all the desired conditions of exposing 

 all the surface of the fish to the brine, flowing the brine with great 

 rapidity, avoiding sluggish film on the surface, holding the fish 

 straight as they freeze, and avoiding abrasion,. 7. By using a spray 



