REFRIGERATION OF FISH 621 



the freezing process before they are frozen through. The freezing 

 point of salt-water fish is about 30.7° F. and of fresh-water fish about 

 31°. The respective classes of fish may be chilled to these tempera- 

 tures without freezing. At such temperatures putrefaction and 

 autolysis are not arrested but are greatly retarded. Fish so chilled 

 will keep in good condition for several days. Kyle's method was 

 designed to chill in concentrated sea water, and later, if desired, to 

 freeze the fish. Dahl's method chills or freezes according to the time 

 allowed for pumping the cold brine between the fish. The methods 

 of Ottesen, Goer de Herve, Mann. Pique, Taylor, and Newton also 

 may be used for chilling. 



LARSEN'S METHOD 



J. M. Larsen, of Copenhagen, designed a method sv particularly for 

 chilling fresh fish. He uses clear filtered sea water chilled to about 

 32° F., or a little colder. The fish are kept in this bath until they are 

 chilled to a temperature approaching their freezing point, but not 

 frozen. He also specified salt water in lieu of sea water and of about 

 the same concentration. In this mild brine he claims that penetration 

 does not occur, and that after 10 days the eyes are bright and gills 

 pink, while gutted fish keep from two to four weeks in a much better 

 condition than fish preserved by the usual methods. 



There is a widespread assumption that because sea water is the 

 natural element in which fish live it is inert and harmless as a bath- 

 ing medium for dead fish. The nearest to an ideally inert solution 

 for this purpose would be water containing the same mineral sub- 

 stances in solution in the same proportions in which they occur in fish. 

 This is not true of sea water for any common food fish. Sea water 

 contains about 3.5 per cent salts and a larger proportion of mag- 

 nesium chloride than occurs in fish. Haddock contains about 1.45 

 per cent mineral salts in quite different proportions from those of 

 sea water. The living fish is able to resist and regulate the osmotic 

 penetration of the excess salts in sea water, but when dead it is not 

 able to do so. Therefore there will be an interchange between the 

 piece of fish and sea water when fish are bathed or chilled in it. 



EATON AND CAMERON'S METHOD 



A method 88 similar to Larsen's was designed by Eaton and Cam- 

 eron, but differing from it principally in the use of ordinary salt 

 brine 80 per cent saturated and flowing at a temperature of 12° to 15° 

 F.. wherein the fish are reduced to a surface temperature of 27° to 29° 

 F. in 30 minutes without freezing. The principles underlying the 

 effect of temperature and concentration of brine on the rate of pene- 

 tration (see p. 578) indicate that under these conditions the fish would 

 absorb much salt. A temperature of 12° may be reached satisfac- 

 torily in brine only 54 per cent saturated, and such a brine certainly 

 would not penetrate as rapidly as the much stronger brine specified 

 by these inventors. However, the inventors' first claim covers any 

 temperature and concentration that will cool fish from 38° to 27 3 or 

 29° F. in 30 minutes. 



87 U. S. Patent 1322312. Nov. IS, 191!). For .1 reeenl account of plans and claims for 

 this method see '• Politiken " i Copenhagen), Aug. 12, 1925i 



88 A. C. Eaton and W. R. Cameron, U. S. Patent 1404352, Jan. 24. 1112^. 



