tubes, running from the inside of every trap-seal to the larger air-pipes extending through the roof of the building. With this double ventilation, the deleterious effect of air-currents on trap-seals is, of course, greatly increased.
Some idea of the complication and enormous expense of this system may be formed from an illustration of its application to a group of four plumbing fixtures in adjoining rooms on one floor of an elegant residence recently built in New York city (Fig. 1). It will be seen that the air-pipes require an almost complete duplication of the waste and soil pipes. This, of course, adds greatly to the cost of the plumbing, and increases the danger from imperfections in the largely augmented number and length of pipes with their multifarious joints.
Fig. 2 shows the same number of fixtures in the same relative position, but the plumbing is arranged in accordance with the requirements of modern methods as developed by the application of scientific principles.
Not long after the adoption of the fallacious device of back-venting, it became evident that more efficient means of guarding against the dangers of sewer-air were necessary, and persistent
Fig. 5.—Second Step in the Development or an Anti-siphonic Trap.
effort was directed toward devising better methods of house-drainage. The result has been the attainment of a new order of things by the recognition of scientific principles previously ignored.
For the development of this science, credit must be given mainly to an accomplished sanitarist of Massachusetts, Mr. J. Pickering Putnam, whose experiments and investigations on subjects relating to household sanitation are unquestionably the most thorough and complete that have ever been put on record. The first of this series of experiments was made for the Board of Health of Boston, in 1883. Subsequently, special demonstrations
