564 



u. 



BUREAU OF FISHERIES 



(which may approach zero if necessary). Such a truck is shown in 

 Figure 21. 



Dry ice or carbon-dioxide ice, next to be described, also may be 

 used. A closed van should be loaded and from 100 to 200 pounds of 

 crushed dry ice thrown over the boxes. A very rapid fall in tem- 

 perature occurs, and the fish keep, frozen hard, for several hours 

 in hot summer weather. 



SOLID CARBON-DIOXIDE REFRIGERANT FOR TRANSPORTATION 



As a means of refrigeration of cars for the transportation of fish, 

 solid carbon dioxide has shown promise in trials. Although the ap- 

 plication of this substance to the preservation and transportation of 

 fish in commercial practice is still (August, 1926) too recent and ex- 

 perience is too limited to justify a prediction of its possibilities in 

 the fish industry, yet it is being used for other products, and its pos- 

 sibilities for fish warrant a description of its properties. 28 



Carbon dioxide is familiar as the gas used in soda water. It is of 

 widespread distribution, being present in small amount in air. It is 

 produced by combustion of coal, wood, gas, etc., and may be recovered 

 from flue gases. It is a noncombustible, nonpoisonous, invisible, 

 heavy gas. When compressed to about 1.000 pounds per square inch 

 it liquefies at about 80° F., and if the pressure is suddenly removed 

 from the insulated liquid carbon dioxide some of it evaporates, and 

 in doing so absorbs so much heat that the remainder freezes to a 

 white, snowy substance having a temperature of about 109° F. below 

 zero. This white " snow " is then compressed into bricks or other 

 desired shapes. This compressed carbon-dioxide " ice," as its manu- 

 facturers have named it, weighs 70 pounds per cubic foot, as com- 

 pared with 57 pounds per cubic foot of water ice. It contains about 

 1.7 times as much refrigeration per pound as water ice, or about 

 2.1 times as much per cubic foot. The amount of refrigeration avail- 

 able in this solid carbon dioxide, expressed in B. t. u. per pound of 

 gas evaporation, and the gas warming to various temperatures is 

 shown in Table 15. 



Table 15. — Refrigeration available in solid carbon dioxide 



Eight cubic feet of the gas weigh 1 pound. The gas, at 32° F., has 

 a specific heat of about 0.18. If this gas is at 109° below zero, F. as 

 it comes from the ice, it absorbs only about 25 B. t. u. in being warmed 

 to 32°. But this same gas, in passing from the solid to the gaseous 

 state, absorbed 255 B. t. u. The refrigerating effect of the gas is 

 therefore only about one-tenth of the ice from which it was produced. 



28 Elworthv. British patent 7436 (1S95), U. S. patent 579866, Mar. 30, 1897; Slate, 

 T. B., U. S. Patents 1511306, Oct. 14. 1924, 1546681, 1546682, July 21, 1925. 1563112, 

 Nov. 24, 1925, and 1595426, Aug. 10, 1926. 



