REFRIGERATION OF FISH 565 



The heat absorbed by the ice in its changing state must therefore 

 reach the ice by direct conduction from objects in contact with it or 

 by convection of the gas current. These facts have a significant bear- 

 ing on the applications of this " ice " to refrigeration. 



The term " dry ice " is used advisedly, for it does not melt to a 

 liquid as water ice does, but, in absorbing heat, is converted directly 

 into the gaseous state, the gas formed being also very cold until it, 

 too, absorbs more heat. This gas is about one and one-half times as 

 dense as air and consequently will sink to the bottom of an inclosed 

 chamber, displacing the air. If sealed tight it will exert a powerful 

 pressure, but if a means of escape is provided it passes out into the 

 atmosphere. 



Solid carbon-dioxide " ice," though very cold, may be insulated 

 and transported for short distances, but with some loss, of course. It 

 may be used for chilling a chamber, the temperature being regulated 

 by insulating the solid to control the rate of evaporation. If blocks 

 of it are placed in the upper part of a chamber they rapidly absorb 

 heat and give off cold gas, which displaces the warm air, sinking to 

 the bottom and gradually filling the entire chamber and surrounding 

 contents. If much of the solid is used, with little or no insulation, 

 the chamber may be chilled to an extremely low temperature: but if 

 a small quantity is used, with heavy insulation, the chamber may be 

 kept cool without freezing. 



This gas has other useful properties. By displacing the air it 

 arrests oxidation completely. This fact is probably of advantage in 

 fat fish in preventing oxidation of fat (when air is present, oxida- 

 tion actually produces heat). Many kinds of bacteria require oxy- 

 gen, and when oxygen is displaced by carbon dioxide they either die 

 or become inactive. By dissolving in the juice of the fish carbon 

 dioxide produces a mild, harmless acid (carbonic acid), which also 

 combats some bacteria. Carbon-dioxide ice is thus not only a refrig- 

 erant of valuable properties but its gas is an aid to preservation as 

 well. It evaporates and disappears when the fish are taken out of 

 it, leaving no taste or other objectionable trace. 



USE OF CARBON DIOXIDE ICE IN THE SHIPMENT OF FISH 



The pioneers in the manufacture and application of solid carbon 

 dioxide to refrigeration and preservation of food 29 arranged, at the 

 request of the Canadian Department of Marine and Fisheries, to 

 send a trial car of fish from Halifax to Montreal, the distribution of 

 the fish to the trade being arranged by the Canadian Fisheries Asso- 

 ciation. 30 A refrigerator car was equipped at the four corners (out- 

 side the ice bunkers) with cylindrical metal containers 12 inches in 

 diameter and TO inches high, in which cylinders of solid carbon 

 dioxide were placed, the entire charge weighing 850 pounds. 



The car was packed at Halifax with an assortment of frozen fish 

 and fish on ice and sent to Montreal, being four days en route, and 

 allowed to stand on the tracks two days — six days from the time of 

 sealing. When the car was opened the air (or gas) temperature was 

 33° and all the fish were in excellent condition. 



=» The Drv-Ice Corporation of America. 50 East Forty-second Street, New York City. 



30 For full report on this shipment, see reports in Canadian Fisherman, Vol. XI, May, 

 1924, pp. 111-120. Gardenvale, Province of Quebec. There are numerous technical errors 

 in the report. 



