42 MADRAS FISHERIES BULLETIN VOL- XIV, 



in operation, (h) retention of the natural appearance of fresh fish, 

 (r) less loss of weight, (d) better keeping qualities when thawed out, 

 (i') perfect naturalness of flavour and table appearance when cooked. 



Celerity. — By any of the perfected brine-freezing methods herring 

 can be frozen to the bone within half an hour, sprats in twenty 

 minutes. If air-freezing were employed, at least twenty-four hours 

 would be required. In the case of larger fish of about six pounds 

 weight the period to freeze completely takes from one and a half to 

 two hours compared with from, thirty to thirty-six hours in 

 air-freezing. Consequently in brine-freezing the time required to 

 freeze a fish is from fifteen to twenty times less than if ordinary 

 air-freezing be employed, obviously an advantage of the greatest 

 value in the application of the freezing process to commercial 

 purposes, and particularly in cases of sudden gluts. 



The reason for the greater rapidity of the freezing process in an 

 aqueous salt solution, " brine " as we term it, over the sharpest of 

 sharp-freezing in air, even at much higher temperature than in the 

 latter, is due to the fact that brine is much more efficient than air 

 in abstracting heat from objects immersed in it. This follows 

 principally from the great conducting power of water; air has a 

 contrary property and is indeed an insulator, a property made use 

 of daily by the employment of air spaces within walls to prevent 

 the passage of heat. In freezing, therefore, the heat of the object 

 treated is abstracted at a far greater rate when brine is employed 

 than air. 



To those who have no acquaintance with freezing principles, 

 it may be mentioned that the reason solutions of salt (brine) are 

 used is due to the fact that these mixtures have a much lower 

 freezing point than pure water. The more highly concentrated 

 the solution, the lower the freezing point. That of concentrated 

 solution of common salt (sodium chloride) is — 2r2*' C. { — 6'l6° F.), 

 whereas for calcium chloride it is — 55° C. ( — 58° F.). Because there 

 is some penetration of the salt used, though it be very slight indeed, 

 it is in practice found preferable to use a solution oi common salt; 

 this permits of the maintenance of a temperature quite low enough. 

 Saturation is not necessary in practice and a satisfactory working 

 solution is obtained by the addition of 3 lb. of common salt to 

 each gallon of water. 



The initial temperature of the brine before the immersion of the 

 fish should be in the neighbourhood of — 15" C. (5* F.) ; fish do not 



