CRANE.| Prospecting, Mining and Milling Machinery. 257 
parts of the cars are cut to pattern, so that they will fit per- 
fectly, and thus save time in setting up. A slightly different 
form of pit car is shown at 3, figure 45. Surface tramway 
cars designed for rather long distance hauling, and con- 
sequently for heavy loads, are constructed as follows: Two 
sets of timbers consisting of two 4x4 or 4x6 inch oak planks 
are used for bed pieces. The axles are fastened to these, an 
axle to a set, and are cross pinned or bolted to the bed pieces 
to hold them in place. The bed pieces are now placed end to 
end and fastened together by two heavy wrought iron hinges. 
This arrangement holds the wheels, when the bed pieces 
are horizontal and therefore lie in the same plane, about 
eighteen inches apart. A bed of plank is then put together 
and fimly bound by means of straps of iron two inches wide 
by one-half inch thick. The sides consist of 2x 10 inch oak 
plank, the lower ones standing vertically, while the top ones 
flare out, increasing the width of the bed from two feet five 
inches at the bottom of this plank to three and one-half feet 
at the top. One end of the car is left open and is provided 
with a door which is hinged at the top. This door is held 
in place by a catch operated by a lever. The body of the car 
is placed upon the bed timber, but is bolted to only one set, 
the set next the end gate. An examination of / and 2, figure 
45, shows both the method of construction and of dumping. 
A slight pull on the back end of the car, the lever being pushed 
to one side, causes it to dump, the door or grate being freed 
by the lever; thus the car is emptied of its contents. 
Another form of dumping hand car often used in the jig 
room to handle concentrates is shown in 4, figure 45. The 
construction and working of the same are shown in the figure 
referred to above. 
3 SIZING APPARATUS. 
CHUTES AND SCREENS.—There are three forms of screens 
employed in the sizing of ores, namely: Parallel or bar screens, 
commonly called grizzlies; shaking screens, or riddles; and 
revolving screens (drums or trommels). Of these, the first 
and last given are the forms in most common use. 
Parallel bar screens were formerly rarely used in connection 
