322 MARINE PRODUCTS OF COMMERCE 



Table 85. Relation between Salt Content and Possible Temperature for 

 Salt and Ice Mixtures. 



„ ,^ ^ ^ Freezing Salinometer 



Salt content, „ ^. . . ^■ r 



Ratio point reading or 



true per cent i^ ^ . , i . ^ 



, . 1 ^ salt to ice degrees brine at 



by weight ^p^S ^^^ g(j,p (^gg,^^ 



5 5.3 27.5 -2.8 18.8 



10 11.1 20.4 -6.4 37.2 



15 17.6 12.5 -10.8 56.8 



20 25.0 2.6 -16.4 75.2 



23.3 30.4 -6.0 -21.1 87.6 



these are refrigerated by eutectic inserts or "Dry Ice." The containers are in- 

 sulated and are precooled before the perishables are loaded and the inserts 

 added (Anon., 1943). 



Trucks and Trailers 



Trucks and trailers are becoming more and more important in the transport of 

 fresh and frozen foods, particularly in the shipment of such perishables as fish. 

 This is due to the great advances that have been made in the refrigerating equip- 

 ment used in trucks and trailers, which result in temperatures being held closer 

 to those recommended than are held by railway equipment. The improvements in 

 design and refrigerating equipment have added tremendously to the range of the 

 truck so that, whereas 3 years ago a truck would make a 300-mile trip, it is now 

 making a 1,000-mile trip, and the damages to cargo are certainly no greater. 

 For long hauls the railway refrigerator car is still the most important vehicle; but, 

 if freight rates continue to increase, the truck and trailer will become serious 

 competitors, even for long hauls. It is probable that even though truck rates are 

 somewhat higher than rail freight rates, trucks will continue to gain favor because 

 of their greater flexibility, better service, and better holding conditions. Unless 

 railway companies improve their facilities, trucks and trailers may take over the 

 major portion of the carriage of perishable traflBc. 



Unlike railway cars, which are usually of standard dimensions and construc- 

 tion, the refrigerated trucks are made directly to suit the needs of the owner, 

 not only in size, but in insulation and refrigeration equipment also. That is, some 

 are designed for short hauls with moderate insulation, while others are built for 

 long hauls involving both cooling and heating equipment. 



The development of refrigeration equipment for trucks and trailers seems to 

 be well in advance of that for railway cars, for there are thousands of trucks in 

 the United States equipped with mechanical or other types of refrigeration facili- 

 ties in operation now. 



The types of refrigeration equipment most favored are the "Dry Ice," the 

 hold-over plates, and the mechanical types. Since each type has a special applica- 

 tion for which it is best suited, it is likely that all three will continue to expand. 

 The "Dry Ice" systems have been described under the previous sections in railway 

 refrigerator cars. 



Hold-Over Plate System. The hold-over plate system is one that is favored for 

 short hauls or for local deliveries, where trucks can be serviced nightly at the 



