TRANSPORTATION OF FISHERY PRODUCTS 325 



coarse ice to ice down their fish. The fact was overlooked that in attempts to 

 conserve ice the primary purpose to preserve the catch was being jeopardized. 

 Obviously, the finer the ice the better the preservation of fishery products. 



Velocity of the Surrounding Air. Intuitively it will be gathered that the rate of 

 ice melting will depend a great deal on the velocity of the air passing over the 

 exposed surfaces of the ice. The higher the velocity the greater the rate of melting. 

 According to a report of work done by Paul W. Scates at the University of Ten- 

 nessee in 1931, every square foot of exposed ice area may produce an added 

 pound of water for every increase in velocity of the air of 400 feet per minute. 

 That is to say, if other factors remain constant, then an increase in the velocity 

 of the air from 100 to 500 f.p.m. would increase the ice melting by approximately 

 1 pound for every square foot of ice exposed to the moving air. A practical ap- 

 plication of this knowledge dictates that ice and iced fish be protected from 

 moving air. 



Humidity. Although it might not be readily appreciated, the relative humidity of 

 the space surrounding ice has a significant effect upon its rate of melting. This is 

 clearly indicated in the report of the Tennessee experiments just referred to, and, 

 as might be expected, the efifect is an increase in the melting rate with increase in 

 relative humidity. The explanation is based on the greater amount of water 

 condensed out of the smrounding space, giving up its latent heat of vaporiza- 

 tion to the ice and thus increasing the rate of meltage. 



"Aged" and "Green" Ice. Although the "age" of ice or its storage life has no 

 efifect on its rate of melting, as late as 1938 it was held as an important factor by 

 many fishermen. These fishermen were so serious in their beliefs that they would 

 refuse to use what they termed "green" ice, that is ice that had been freshly made, 

 even though its temperatmre might be 10 or more degrees blow its melting point. 

 It was necessary to demonstrate, in a practical way, that the length of time ice 

 was kept in storage had no effect on its heat absorbing capacity once temperature 

 equilibrium had been reached. Experiments were performed at the Pacific 

 Fisheries Experimental Station of the Fisheries Research Board of Canada and 

 involved not only determinations of the latent heat of fusion of ordinary ice 

 stored for different periods, but included actual melting rates and temperatures 

 attained under similar conditions for the different ices (Young, 1938). 



Although it is not known how the idea was conceived that storage period had 

 any effect on the thermal properties of ice, it could have arisen from the observa- 

 tion by fishermen that ice that came out of storage appeared to have greater 

 heat-absorbing capacities than that of ice just out of the freezing tank; this was 

 attributed to the storage rather than the lower mean temperatiire. Simple 

 calculations show that the heat-absorbing capacity of ice is increased 1 per cent 

 for about every 3 degrees lowering in temperature below its freezing point; 

 therefore, the storing of ice has the effect of permitting the ice to reach equilibrium 

 with its surroundings. For practical purposes this requires hours rather than days 

 or weeks. The practice of storing ice at 20° F (— 6.7° C) or lower seems to be 

 gaining favor, and this lowering of temperature about 12° F (6.7° C) below the 

 freezing point increases its heat-absorbing capacity about 4 per cent. 



