Testing. When the piping is all in place the outlets are to be capped and the whole system tested for leaks, and accepted by the local gas company. This test consists, briefly, in attaching to one of the outlets a mercury gauge, and then filling the pipes with air under pressure till the mercury in the gauge stands to the required height to insure tightness, which is usually six to twelve inches. The apparatus is then left to stand for ten or fifteen minutes, and if the mercury still holds the same level it is safe to say that the pipes are tight. Leaks may usually be detected by the sound of the escaping air, but often ether is put into a cup attached to the pump and forced in with the air, so that leaks, especially in concealed parts of the pip ing, may be detected by the odor of the ether. Suspicion of a leak in pipe or fittings may be verified by brushing strong soap-water over the place, when a bubble will be blown by the escaping air. Small pin holes in the pipe or couplings may be tamped, and if thus rendered tight will remain so, but pipes showing a split or large hole must be replaced.
Electric Wiring. All coun try houses, unless in very re mote situations where there are no chances of an electric current ever being obtained, should be wired for electric lights. The usual method is the knob and tube system, where the wires, of copper heavily insulated, are run between beams and studs on porcelain knobs, and in short porce lain tubes where passing through timbers. (Fig. 35.) Although the
insurance exchanges, employ inspectors and require that every job of wiring shall be reported to them and inspected by their men, it will be well for the superintendent to carefully watch this construc tion to see that all wires are thoroughly insulated and at least 3 inches apart to avoid any chance of contact, that they are not allowed to sag, and that the joints are properly protected by a free use of insu lating tape. Upon brick or stone walls, and in all places where there is danger of injury, wires should be run in conduits or pipes. In this case the angles and bends of the conduits must be made in easy curves so that the wires may be easily "drawn in". All wiring should be tested when installed and again at completion of the build ing, to insure against any mechanical injury. For electric bells, it is usual to run an insulated wire secured to the studs by staples, and care must be taken to see that bells as well as Iight outlets are placed in convenient places. If the bells are to be operated mechanically the wires should be run in zinc tubes, but as such wires stretch and break in time, the electric wires are generally preferred.