In each case the source of power for operating the mixer, conveyors, hoists, derricks, or cableways must be considered. If it is possible to run the machinery by electricity, it is generally economical to do so. But this will depend a great deal upon the local price of electricity. When all the machinery can be supplied with steam from one centrally located boiler, this arrangement will be found perhaps more efficient.

Fig. 131. Interior View of Trump Concrete Mixer

Fig. 131. Interior View of Trump Concrete Mixer.

In the construction of some reinforced-concrete buildings, a part of the machinery was operated by steam and part by electricity. In constructing the Ingalls Building, Cincinnati, the machinery was operated by a gas engine, electric motor, and a steam engine. The mixer was generally run by a motor; but by shifting the belt, it could be run by the gas engine. The hoisting was done by a 20-horsepower Lidgerwood engine. This engine was also connected up to a boom derrick, to hoist lumber and steel. The practice of operating the machinery of one plant by power from different sources, is to be questioned; but the practice of operating the mixer by steam and the hoist by electricity seems to be very common in the construction of buildings. A contractor, before purchasing machinery for concrete work, should carefully investigate the different sources of power for operating the machinery, not forgetting to consider the local conditions as well as general conditions.