24 STUDIES OF POULTRY. 



The refrigerator cars used by the various railroads, or even by the 

 same road, differ chiefly in the degree of insulation furnished. Thus 

 the cars may vary in efficiency because of lighter construction and in- 

 sulation or because of a variation in the insulating material itself. 

 The tendency on the part of the railroads at the present time is to 

 increase insulation. Cars are built more heavily, and much greater 

 care is given to the selection and amount of the insulating material. 

 There is considerable variation, also, in the construction of the com- 

 partments at the ends of the car for holding the ice, or the ice and 

 salt, upon which refrigeration depends. These " ice bunkers " are 

 built with the hope that their construction will produce some circula- 

 tion of the cold air in the loaded car. At the present time this is one 

 of the problems at which the railroads are diligently working, and 

 there are numbers of types of experimental cars now being tried, all 

 having this object in view. 



The efficiency of a car is affected also by its ability to withstand the 

 usual wear and tear of traffic. Frequently doors are jarred, rendering 

 the insulation about them imperfect ; joints crack, or the shipper, to 

 prevent his load from shifting, may drive heavy spikes into the walls 

 of the car, thereby doing great damage to the insulation. 



THERMOGRAPH RECORDS. 



Curves are reproduced (see fig. 7) to show the variation in tem- 

 perature in a single car which had suffered hard usage and which 

 was very badly insulated about the doors. It was iced for twenty-four 

 hours before loading with finely chopped ice mixed with 10 per cent 

 df salt, and loaded in the center with eggs which had been chilled 

 before shipping, while at the bunker ends were boxes of chilled 

 poultiy. 



Figure 1A show^s the temperature record of the air of the car around 

 the upper layer of poultry boxes next to the eggs, which occupied 

 about the width of the door space in the middle of the car. It will 

 be observed that the temperatures here varied betwen 45 and 50 F. 

 (7 and 10 C.), and that nearly nine hours were required before the 

 minimum temperature was reached. Figure IB shows the car tem- 

 perature in the upper layer of boxes at the bunker ends. Here the 

 temperature varied from 25 to 35 F. (4 to 2 C.), with generally 

 the maintenance of a temperature less than 30 F. ( 1 C.). Figure 

 1C shows the temperature maintained on the floor of the car next 

 to the ice bunker, and here the general average would lie between 10 

 and 20 F. (12 and 7 C.), while the maximum is not over 25 F. 

 (-4 C.). 



The type of car now prevailing, if it is in good condition, will main- 

 tain a temperature of less than 40 F. (4 C.) opposite the doors 



[Cir. 64] 



