Before the plastering is begun, the pipes for gas and the conduits for electric wires, must be run. These, being small, may be concealed, if desired, although the idea of exposing gas piping is becoming more in vogue, especially where thin partitions are used. When hollow blocks are used for the partitions it is customary to channel them for the rising pipes and conduits; while the horizontal pipes are usually bedded in the concrete filling over the floor construction. (Fig. 247.) Sometimes the horizontal pipes are run under the floor beams, the suspended ceiling being dropped low enough to allow free circulation for the pipes. Sometimes the pipes are run between the floor beams; but if the girders are framed flush, it will be necessary to punch holes in them, and lateral branches cannot be easily managed. Where no partitions are available in which to run vertical pipes, as often occurs in the lower stories, the casing of the steel columns may be enlarged, so as to allow of pipes being run up, but if this is done, a separate flue outside the column casing, as in Fig. 248, should be made, as the insertion of pipes or conduits directly into the column casing destroys its fireproof value to a large extent, beside subjecting the steel to the action of injurious gases.