b. Refrigerator and heater cars. Two special types of enclosed cars used to transport perishables are
refrigerator and heater cars. Refrigerator cars are usually equipped with one of three basic cooling systems:
chunk ice, brine made of crushed ice and salt, or mechanical cooling systems. Heater cars have either temporary
or permanent heating systems using charcoal, alcohol, coal, or propane gas for fuel.
c. Stock car. The principal difference between the construction of stock cars and boxcars is that the sides
of stock cars are slatted with air space between to permit a free circulation of air for livestock. These cars are of
either the single- or the double-deck variety depending upon the size of the animals to be hauled. Stock cars are
often used to ship produce, such as lettuce and cabbage; they are also used to ship lumber, brick, and tile that
need no protection from the weather.
Because of the wide variety of freight hauled in gondolas, their designs vary greatly. Often referred to as
"the donkey of the rails," gondolas may have high and low sides, end and side doors, drop doors in the floors or
at the ends of the car, and swinging side doors. Depending on their construction, they are referred to as solid-
bottom, drop-bottom, hopper-bottom, side-dump, and well-hole.
Gondolas are used to transport such things as steel products, lumber,
brick, coal, ore, machinery, and large cargo containers.
One rail line in the United States has recently put into operation a fleet of gondolas with all-white interiors
as an aid to loaders working at night. It seems that crane operators, loading steel pipe for example, have always
had trouble estimating how far their loads were from the bottom of the gondolas. Black interiors against the
night darkness offered no contrast; operations were slowed down and loads were frequently damaged when they
were slammed down too hard. Now, with interiors painted white with a special light-reflecting paint, loadings
at night are faster and gentler on the lading.
Designed primarily to haul coal, the hopper is similar to the gondola except that instead of level floors it
has floors that slope from the ends and sides to hopper doors through which the load can