34 BULLETIN 1077, U. S. DEPARTMENT OF AGRICULTURE. 
doors provided with a locking mechanism so that they can be re- 
leased separately. (See Fig. 1, PI. IV.) The number of compart- 
ments will depend upon the size of the batch and the capacity of 
the truck. For truck haul the proper proportions are obtained by 
the use of measuring hoppers attached to the bins in such a way 
that the materials will flow into them by gravity and discharge into 
the trucks by the same process. A measuring hopper should be pro- 
vided for each kind of aggregate. Where the aggregates are handled 
from a single divided bin it is possible to arrange the measuring 
hoppers so that they can both be discharged into the truck at one 
operation. This arrangement is much preferable to the use of two 
separate and distinct bins for the aggregates, as the time of load- 
ing is practically' cut in half. After the truck has received its load 
of proportioned aggregate it is driven past the cement house, where 
the proper amount of sacked cement is thrown into each compart- 
ment. As the truck is turning around on the road preparatory to 
backing to the mixer the sacked cement is emptied into the compart- 
ments. Where light trucks are used, the sacked cement is sometimes 
carried on the truck frame, just back of the driver's seat, and un- 
loaded and emptied into the mixer skip by hand as the truck is dis- 
charging. The purpose of hauling the cement to the mixer in sacks 
is to avoid any loss occasioned by high winds. In dumping trucks 
containing more than one compartment, the dump body is raised 
and the end gate released, allowing the first batch to run into the 
loading skip. The truck is then run forward sufficiently to give 
clearance for the raising of the skip. After the skip is discharged 
and lowered the truck backs into position for unloading again and 
the first swinging compartment is released for the discharge of the 
next batch. With efficient truck operation and a good road to haul 
over this method of operation may be successfully employed. 
The industrial railway is particularly well adapted for hauling pro- 
portioned batches. By this method the materials are hauled in re- 
movable car bodies or in batch boxes set directly upon the frame or 
platform of the industrial cars, from which they can be lifted by a 
suitable hoisting device. (See Fig. 2, PL IV.) Greater train 
capacity is obtained with batch boxes, and they are the more widely 
used than cars with removable bodies. Three general types of batch 
boxes are used, distinguished by their method of discharge, as fol- 
lows: (1) Tip-over boxes; (2) side-discharge boxes; (3) bottom- 
dump boxes. These boxes are generally rectangular in shape and 
are constructed either of steel or wood. The wood box has one 
important advantage over the steel box ; it can be easily repaired in 
case of a train wreck, while steel boxes, once they have become bent, 
are difficult to straighten. The tip-over box is provided with trun- 
