Of course, it will be objected at first thought that the pneumatic test does not reproduce in actual form the precise phenomena encountered in ordinary plumbing work, but a little reflection will show that the results are identical so far as they affect our inquiries. The agency which produces siphonage is the partial vacuum in the soil pipe, and this rarification is effected by the rapid movement of a piston. Whether the piston be in the barrel of a pump or whether it be in the soil pipe itself is altogether immaterial so far as concerns the effect of the partial vacuum on trap seals. The pneumatic apparatus possesses the great advantage over the hydraulic of enabling us to vary the force of the strain applied to the traps to any extent desired, while only one degree of rarification can be obtained by the falling water plug in any one plant. The siphoning action in both cases is extremely rapid, almost instantaneous.

In the case of the falling water piston, the action takes place in the flash of time required for the piston to pass by the small mouth of the branch waste pipe serving the trap. A fraction of a second suffices for this.

In the case of the air pump apparatus the speed of the action is measured by the time it takes to move the valve lever connecting this branch waste pipe with the soil pipe. This requires but a fraction of a second, and the speed may be regulated to correspond accurately with the hydraulic action. Moreover, a vacuum gauge may be applied to the soil pipe in both kinds of apparatus and thus the action may be proved to be in both cases identical in speed, power and effect. The duration of the siphoning strain may be increased by increasing the size of the main pipe representing the soil pipe from which the air is to be exhausted.

In order, however, to be satisfied as to the similarity of the effect produced on the gauge and trap seals, one has only to have erected side by side apparatus of both kinds, as the writer has done before several audiences, and it will be found that when the vacuum gauge registers the same degree of rarification in both soil pipes, the effect on the traps in each is the same.

It is possible on our pneumatic apparatus to produce a strain equal to a vacuum of twenty-six inches, and yet we find the large sizes of drum traps and other anti-siphon traps capable of resisting, unvented, this strain even many times repeated without refilling. The first application of the strain lowers the seal considerably, the second and third less, and thereafter subsequent applications without refilling have little effect upon it, and finally a point is reached when no appreciable further reduction can be attained, however often the strain is repeated

The vented S trap, on the other hand, is incapable of resisting a vacuum of a single inch when the vent pipe is long and crooked, or when it is partially roughened or closed by deposits. A few inches of vacuum will destroy its seal even when the vent pipe is new and clean and as short and straight as it is possible to make it in practice.

The apparatus shown in Figs. 271 to 273 inclusive are easily and cheaply constructed of brass tubing, polished and nickel plated, with a vacuum pump constructed with special accuracy so as to enable it to produce and maintain a vacuum as perfect as is possible. There is, therefore, no excuse for any board of health or plumbing inspector's office to be without such a plant, because its use would demonstrate the folly of the trap vent law and save to the citizens, by its repeal, more than the entire cost of the apparatus in a single good-sized building.

Fig. 273 is a very small, compact form of portable apparatus devised by the writer for lecture service. It measures less than two feet in height and if constructed of aluminum may be very conveniently transported by hand in a canvas or light leather case.

A simple hydraulic apparatus may be constructed and used side by side with the pneumatic outfit where it is desired to demonstrate the identity of the results produced by the two systems. But, as before said, the usefulness of the hydraulic plant is limited to a very narrow range of tests and it is less accurate and comparatively unscientific. It involves, moreover, the consumption of a very large amount of water where the pneumatic plant can be operated without any expense whatever.

Fig. 273a.

Fig. 273a.

Fig. 273a represents another form of apparatus for lecture service. Its action is entirely automatic. A small electric driven pump shown at the lower tank raises the water continuously from this to the upper tank by the electric current taken from an ordinary electric light fixture, through the small pipe shown at the left side of the tanks.

When the upper tank if full it discharges automatically, and its discharge operates alternately the valves connecting the traps with the central waste pipe so as to produce upon them the siphoning action, and thus makes simultaneously a comparative as well as an absolute test of any traps desired. The central ratchet wheel governs the siphoning and refilling of the traps. The action continues as long as the current is kept on, and the tests are thus made at a minimum of expense with a maximum of convenience.

With either of these simple forms of testing apparatus one stands entirely independent of outside testimony as to the relative efficiency of the trap venting and of the anti-siphon systems, and can see for himself in a few minutes the truth in such controversies as have been published, relative to the Worcester tests, for instance.

There is no excuse whatever for any doubt in the matter, and no one thereafter would dare to publish any inaccurate or misleading statements in this very important domain, knowing that any board of health or building inspector's office can authoritatively refute such misstatements at once. In order to make the tests of the efficiency of different traps on our pneumatic apparatus, it is necessary to first close all the stop cocks shown in the drawings by wheel or lever handles between the traps and the main pipe, and exhaust the air in this pipe by means of the vacuum pump, until the vacuum gauge shows the degree of rarification desired to correspond with what would be encountered in any case of plumbing to be represented.