Iron Piping. If the cost of brass piping proves to be excessive, a good quality of iron pipe may be substituted where there is danger of corrosion of lead or of its bursting by great pressure. Iron pipe may be obtained with a lining of block tin, which forms a pure and very satisfactory channel, or a galvanized or zinc coating may be used which will be less expensive. The same methods of piping will be necessary in running iron pipe that we have mentioned in piping with brass, and besides, we must take precaution against condensa tion which will take place upon iron pipes in warm weather, from the fact that iron conducts heat so rapidly. This condensation will be so great that it may on occasion trickle clown and cause damage to paper or decorations. Where there is this danger, the pipes should be run in tubes of zinc which will conduct the water to a safe outlet. This precaution should be taken, even in the case of lead or brass piping, when costly decorations or papers are liable to injury from bursting or leaking pipes.
The fastening and joining of all pipes should be carefully watched to see that they are run in straight lines, with free angles, and that hot water pipes are separated by a little space from cold water pipes so that there will be no transmission of heat from one to the other. All pipes must be run so that they will pitch toward some faucet or waste cock, which must be provided in convenient places and in sufficient numbers to shut off and drain both hot and cold water pipes in any given part of the house, as well as the whole system. In New England it is customary to supply the bath boiler from a separate tank in the attic, this tank being supplied from the regular service with a ball cock to regulate the supply. The supply from the boiler to the various fixtures is made to return again to the boiler for circulation, which allows hot water to be drawn at once at each fixture. From the highest point of the circulation a small "expansion pipe" is run to the tank and turned over the edge to dicsharge just above the water line, in order to allow the steam and froth from the boiling of the water to escape into the tank. This tank should be supplied with an overflow to some convenient fixture. Outside of New England the tank is generally omitted and the boiler supplied from the house system, but this requires a strong boiler, usually of galvanized iron and is not so satisfactory as the expansion system.
Waste Pipes and Traps. The waste pipe or outlet of every plumbing fixture must have, as near as possible to the fixture, a trap, to prevent foul odors and sewer gas from issuing. The simplest form of trap, and in its improved forms one of the best, is the Strap. (Fig. 44.) This consists of a piece of pipe bent into the form of the letter S, with a screw in or near the bottom to allow of cleaning out. The theory of this trap is that some of the water which passes through will remain in the trap, as shown in the cut. Iu actual use, however, if enough in volume runs through to completely fill the outlet, the falling water will create a vacuum at A, which will cause the outside air to force out the water in the trap until it falls below the bend I3, thus destroying the seal. If, however, an inlet is provided at the
highest point of the trap A, the vacuum in the outlet pipe will be filled from this source without disturbing the water in the trap. This inlet pipe must, of course, be carried to some amain air pipe; and so it is customary to run beside the main soil pipe a line of "vent" pipes to which the different trap vents are attached, the main vent usually starting from the base of the soil pipe and entering the same again above the highest fixture. A greater danger exists where two or more fixtures are connected with the same soil pipe. In this case the seal of the lower fixture will be broken by reason of the col umn of water discharged from the upper fixture, creating a partial vacuum in the soil pipe and the outer air rushing in to fill the void by the easiest way, will force the water out of the trap below. (Fig. 45.) This is a real danger, and should be guarded against by venting the trap as described.
Another way of guarding against svphonage is to make the trap so large that enough water will drain back from the outlet and sides of the trap to restore the seal. This is called a pot or cesspool trap. City plumbing laws in general require the venting of all traps, which should be done in all cases.
Testing. When the waste and air pipes are all in place and the connections for the various fixtures are put in, the whole system should be exposed to an effective test. The simplest and most efficient to employ at this stage is the water test called for by our fications. This consists in closing all ings in the pipes and filling the whole system with water to the top. This may be clone by attaching a hose at the bottom or filling from the top. The superintendent should be on hand to see that the water does not lower in the pipe after standing ten or fifteen minutes, when the system may be pronounced tight. If however, the water level drops it is evidence of a leak where which must be sought out at once. In a tall line of piping the water pressure will be such that defective joints or sand holes in the piping will be discovered by a stream of water, or at least by the trickling of water down the pipe. Imperfect joints, in the cast iron pipes may be remedied by a more careful caulking, but the presence of sand holes can only be remedied by replacing the defective pipes which should be subjected again to the test until the system proves absolutely tight. After all fixtures are set and all connections made another test is usually made. This may be the "peppermint test" or the "smoke test''. In the former test a vial of oil of peppermint, which is sold sealed for the purpose, is taken to the roof and the con tents poured into the top of the soil pipe. A quantity of hot water is immediately poured in and the top of the pipe closed by stuffing in paper or rags. The vapor, charged with the odor of peppermint, is thus unable to escape and will penetrate the whole system.