REFRIGERATION OF FISH 623 



general use on these boats. Because of a prejudice against its use, 

 iced packages were not shipped inland until 1858, when iced packages 

 were shipped to New York as an experiment, whereupon adoption 

 of the method rapidly followed. 



The first use of ice on English North Sea fishing vessels was in 

 about 1868; and with the establishment of a steam-trawling fleet 

 in the eighties the taking of large quantities of ice aboard became 

 the general practice, enabling the vessels to stay at sea as long as 

 two weeks. Ice is now used in the holds of trawlers and in smaller 

 boats for keeping the catch until it can be landed, in boxes and 

 barrels of fish for shipment, in the bunkers of refrigerator cars, in 

 piles to cover fish on the floors of fish houses, and in windows and 

 show cases of retail fish stores. 89 



PROPERTIES OF ICE 



The properties of ice that make it peculiarly suitable for preserv- 

 ing fish are numerous. As a vehicle for refrigeration it costs nothing 

 or very little. The price of ice is largely the price of the refrigera- 

 tion it contains. If any other substance is used to carry refrigera- 

 tion, the vehicle itself may be expensive aside from the refrigeration 

 it contains. Water, the melted product of ice, usually is harmless. 

 Water ice contains more refrigeration per pound than can be put 

 in most other common substances (even liquid air contains less, or 

 only 122.4 B. t. u. per pound, as compared with 144 B. t. u. in water 

 ice), though solid carbon-dioxide u ice " absorbs 249 B. t. u. in 

 warming to 10° F. below zero. The temperature of ice is constant 

 at the convenient temperature of 32° F., and this temperature can 

 not be raised until all the ice is melted. Ice is convenient to handle, 

 split, crush, and apply. 



While the temperature of ice can not be raised above 32° F. without 

 melting it, the temperature can be lowered below 32°, contrary to a 

 prevalent impression, just as can the temperature of any other solid. 

 A cubic foot of ice weighs 56.7 pounds, and the specific heat of ice is 

 about 0.5 ; that is, 0.5 B. t. u. of heat is required to raise the tempera- 

 ture of ice 1° F. without melting it. 



Natural ice is essentially the same as artificial ice. It may or 

 may not be as pure, depending on its source. 90 It is generally cheaper 

 where it is available, the cost being around $2.50 per ton" as com- 

 pared with $4.50 to $6.50 per ton for manufactured ice. Manu- 

 factured ice may be made from ordinary water; but it is more 

 generally made from either distilled water or is blown with a small 

 stream of air during freezing to keep it in motion. When it is 

 frozen in this way the impurities are driven to the center and re- 

 moved, leaving a clean ice of satisfactory purity. Glacier ice is 

 sometimes used in Alaska and other northern countries, but is not 

 considered satisfactory for fish, being very hard and tending to 

 impart a yellowish color to the fish. 



89 For a description of the methods of icing and transporting fish in England see " The 

 handling and transport of fish," by Edgar Griffiths and Crawford Heron. Department of 

 Scientific and Industrial Research, Food Investigation Board, Special Report No. 5, 25 

 pp. London, 1925. 



*"H. S. Cummins (Journal, American Medical Association. Vol. LXVII, p. 751. Chicago, 

 1916) states that the slow crystalization of natural ice tends to purify it — an advantage 

 over artificial ice. 



