REFRIGERATION OF FISH 



571 



time — perhaps not more than a few thousandths or ten-thousandths 

 of a pound — and this of only one-fourth of the heat capacity of 

 water. The temperature of air rises markedly when the fish has 

 given ur only a very small quantity of heat. When its temperature 

 rises, the rate of flow of heat is reduced, the rate of flow being propor- 

 tional to difference in temperature. The heat given off by a 1-pound 

 fish in freezing will raise the temperature of 310 cubic feet of air 

 10° F. 



If the air in a freezing room should remain still, the fish might 

 require weeks to freeze; it is only the circulation of air that makes 

 ordinary sharp freezers practicable. Air in immediate contact with 

 solid objects, however, moves very sluggishly, a sort of static film 

 being formed. Blowing the air by a fan greatly increases the speed 

 of freezing, as has been shown elsewhere ; but this principle seems im- 

 practicable of application in freezing large quantities of fish because 

 of the immense volume of air that would have to be moved. 



It becomes evident, therefore, that if very much more rapid freez- 

 ing is to be accomplished recourse must be had to a medium of higher 

 conductivity and specific heat than air or any other gas. Any liquid 

 is vastly better than any gas, hence the use of brine. The greater 

 rapidity of freezing of fish in brine than in air is shown by the 

 experimental results given by Stiles 33 in Table 18. 



Table 18. 



-Time required to freeze fish of various thicknesses in air at 1-Y 

 and in solutions at l.' t ° and 6° F. below zero 



These figures are illustrative only. In this country air tempera- 

 tures much lower than 14° F. below zero are used regularly, and the 

 brine temperature of 4° F. below zero is much more advisable and 

 more likely to be used than 14° F. above, as in the table. 



At this point it will be well to remember that the object of 

 achieving more rapid freezing is solely to improve the quality of 

 the frozen fish and not to increase the output of a freezer. In every 

 case the amount of fish that can be frozen per day is limited by the 

 capacity of the ammonia machine. Brine freezing will greatly in- 

 crease the speed of freezing of any one fish, while other fish, 

 unfrozen, await their turn. In sharp freezers all the fish are put 



3a See footnote 47, p. 583. 

 22279—27 6 



