36 BULLETIN 1077, U. S. DEPARTMENT OF AGRICULTUEE. 
loading is essential and a tunnel may be desirable, but for a single- 
mixer operation open bins are believed to be preferable. Indus- 
trial cars may be loaded from open bins either by chutes on the sides 
of the bins or by running the cars directly under the bins and 
loading from traps. (See Fig. 1, PI. VI.) After the aggregates are 
loaded into the batch boxes the train is run past the cement house, 
where the required number of sacks of cement are dumped into the 
boxes. The cement house should be provided with a loading plat- 
form at approximately the same elevation as the top of the batch 
boxes. 
A 24:-inch gauge is commonly used on industrial railways for 
pavement construction and the track is generally laid along one 
shoulder of the road. Passing switches are provided where neces- 
sary. Both steam and gasoline locomotives are used to furnish trac- 
tive power. The limiting factor in industrial railway hauling is 
the rate of grade. On sustained grades exceeding 24 per cent the 
speed and capacity of trains begins to be measurably reduced. On 
a 6 per cent grade the capacity is reduced to approximately one- 
fifth of the amount generally hauled on grades of less than 24 per 
cent. The capacity on grades may be increased by the use of geared 
locomotives, but a locomotive of this type is much slower than a 
direct-acting locomotive. The great advantage of industrial railway 
hauling lies in the fact that the subgrade is not cut up by hauling 
over it, and that hauling is affected comparatively little by weather 
conditions. The delay on account of bad weather, therefore, is 
reduced to a minimum. Another important advantage is that the 
aggregates are kept clean and material is not wasted on the subgrade. 
Attempts have been made to haul batch boxes on trucks and on 
wagon trains, but they have not generally been successful. A der- 
rick independent of the mixer is necessary to discharge the boxes 
and it has been found that there is not sufficient room on the sub- 
grade to maneuver these large machines or wagons without losing a 
considerable amount of time. 
A combination of batch-box truck haul and industrial railway 
haul, however, has proved very satisfactory under certain conditions. 
Where the beginning of the pavement is a mile or more from the un- 
loading plant and the road from the plant to the work contains 
grades as high as 5 or 6 per cent, an all-industrial-railway haul is not 
feasible. However, if the road from the plant to the work is in 
good hauling condition, trucks may be used to haul batch boxes to 
the beginning of the new pavement, where the boxes may be trans- 
ferred by means of a portable overhead crane to an industrial railway 
train for the rest of the trip to the mixer. The transfer of 4 batch 
boxes from a truck to the industrial cars may be effected in from 5 to 
7 minutes. (See Fig. 1, PL VII.) The pavement in this case is 
