Inasmuch as the Gas Company lays down full and complete rules governing the sizes of pipes and methods of running them, which must be followed, this portion of the work is not set forth here further than to require that such rules shall be followed. But in carrying out the work no joist is to be cut more than 1 inch deep, and never more than 8 inches from its bearing.

No vertical stud is to be cut more than 1 1/4 inches deep, and no vertical supporting timber or pier under any circumstances.

When complete, the system is to be tested, in addition to the Gas Company's test, with 15 pounds' air-pressure, which must be held for half an hour.