UNDER this requirement the soil-pipes and main stacks of waste-pipes should be thoroughly ventilated from end to end by giving them direct communication with the outer air, both above and below, in such a manner as to produce within them a constant circulation.

The object of this is to dilute the gases of decomposition to such an extent as to render them as harmless as possible, and then to remove them from the premises. But special pipe ventilating has of late been carried to an excess. There is, in fact, at present what might be called a "vent-pipe fever."

Ventilation hastens somewhat the decomposition of the foul matters in the pipes, but not enough to form an active agent in removing solid impurities.

There has of late been a great deal of misunderstanding and idle theorizing on this subject among writers and practitioners of sanitary plumbing. There are advocates of indiscriminate venting who profess a preference for air-pipes even to a thorough water scour, the most radical ones going so far as to affect for the latter a positive disdain, saying, "If compelled to choose between oxygen and suds, we should give the former preference every time."

Let us now, for a moment, abandon theories and authorities and seek for facts to guide us in forming an independent judgment on this very important question.

All unprejudiced and well-informed sanitarians now admit that the special vent-pipe is no longer to be recommended as a protection against siphonage, since a simpler and better means of protection is now to be found in the use of anti-siphonic traps. All admit that the main lines of piping should be thoroughly ventilated. The question in dispute is: Do traps and branch waste-pipes require the application of special vent-pipes to prevent an accumulation within them of deposit and corrosive gases ?

We have made a series of systematic experiments to arrive at the truth in this matter, and have by these been led to the decided conclusion that they are not. The steps leading to this conclusion are as follows:

We have to consider the removal first of solid and then of gaseous impurities. Under the first heading it was necessary to determine:

First. At what rate the removal by oxidation of the refuse matters in our waste-pipes goes on under a ventilating current under the varying conditions possible in practice.

Second. At what rate the accumulation of deposit goes on under the same circumstances.

Third. To what extent a water scour is able to prevent and remove solid deposits without the aid of the special vent-pipe; and

Fourth. To what extent traps and branch waste-pipes are self-ventilated without the aid of the special vent-pipe in good plumbing practice.

I. - Removal of solid deposits by the agency of the vent-pipe.

To obtain an answer to our first question a series of extremely delicate and careful experiments were made, as follows:

The tests were made on pipes evenly coated with deposits found in house drain-pipes and under the conditions met with in ordinary practice.

The maximum rate of removal was first ascertained by performing the tests under all those conditions which are found to be most favorable to it. Thus the rate of oxidation is greatest when the deposit is alternately wet and dry; when the ventilating current is most rapid; when the temperature is highest, and when the largest surface is exposed to the current.

The first experiments were, therefore, performed under these conditions. The waste-pipes used were of the diameter of ordinary branch wastes, 1 1/2 inches, and were 6 inches long. They were connected with a heated flue by means of an ordinary 1 1/2 - inch vent-pipe in the manner usual in practice, so that the ventilating current should traverse the pipes to be tested from end to end. The time of the year was in midwinter, in the months of January and February.

The pipes were uniformly smeared on the inside with substances found in house drains, using, in some, common soil from a soil-pipe, and in others soap solutions found in lavatory wastes.

The deposits were first thoroughly dried in the pipes, in order to enable them to be accurately weighed in the laboratory, and they were afterwards moistened three times a day throughout the tests, about as they would be in ordinary practice.

As types we shall describe the tests on two of the pipes, which were marked No. I and No. II. The first contained soil and the second some of the soapy mixture. The weight of the deposit in No. I, after it had been thoroughly dried in an air bath, was 3.6520 grams; that in No. 2 was 3.1685 grams. The deposits were then thoroughly moistened with clean water applied with a dropping tube, and the pipes connected with the ventilating flue.

The velocity of the air current passing through them was then accurately measured and found to be very strong, averaging eight feet a second, and this velocity was maintained throughout the whole series of tests by means of a stove connected with the main flue, into which the ventilating flue opened.

This movement is unquestionably as rapid as would ever be met with in plumbing practice. The thermometer at the pipe during the tests averaged about 80° Fahrenheit.

Great care was taken throughout to ensure that no foreign substance whatever should get into the pipes tested. No dusting or sweeping was allowed in the room, and only pure water was used to moisten the deposits. In short, every precaution was taken to obtain reliable results.

After an exposure of one week, under these conditions, to the air current, the pipes were again placed in the air bath for one hour and the deposits in them thoroughly dried at a temperature of 2300 Fahrenheit.

Upon weighing, it was found that both deposits had gained in weight. The soil had gained 0.4955 grams, and the soapy mixture 0.0130 grams.

The tests were then repeated under the same conditions for a second week. This time the gain of No. I was reduced to 0.4775, and the weight of No. II was increased to 0.0315 grams.