A manhole chamber (Fig. 36), is built of brick-work set in cement, and the drain or sewer is continued along the floor of the chamber by means of open half-channel pipes set in a bed of concrete. The surface of the concrete should be raised some inches above the edges of the half-channel pipes to prevent the

Fig. 36.

sewage from overflowing on to the floor of the chamber, and it should be floated with cement all over so as to present a smooth and impervious surface. At points along the main channel tributary drains are connected by means of curved half-channels similarly laid in concrete, the junctions being formed by special half-channel junctions being introduced in the course of the

main channel at these points. All street manholes should be fitted with a perforated iron lid to allow of the free circulation of air in the sewers (see p. 88), a bucket or tray being suspended under the perforations to catch any dirt that may enter from the road. In the case of private drains, the manhole lids should be air-tight, with the exception of the terminal one, which ought to be perforated for the admission of air to pass along the drains and up the ventilators at the top ends of the main drain and its tributaries, a syphon trap being introduced at the outlet from the manhole into the sewer or cesspool as the case may be.*

So much for the points that have to be attended to in connection with the laying of drains and sewers. A description of the various forms of traps has purposely been omitted at this stage, as they may more fitly be described when sanitary appliances come to be considered.

As regards the supervision of the work of drain laying, it is impossible to exaggerate the importance of keeping a watchful eye upon the workmen to insure that every detail is attended to. Unless faults are discovered during the progress of the work, they are exceedingly likely to be overlooked altogether, until, sooner or later, serious consequences result. The fact is, men are frequently employed as drain layers who are entirely ignorant of the principles to be observed and the risks to be guarded against, and until it becomes the custom to require such men to be registered, a requirement which is happily becoming general in the case of plumbers, we cannot look for much progress in this department of sanitary work.

CHAPTER V.

SANITARY AND INSANITARY WORK AND APPLIANCES.

THE various appliances connected with the drainage of houses and premises have now to be considered.

In forming an opinion regarding the efficiency of any appliance, experience is the only safe guide, but one thing is certain, that no mechanism is satisfactory which does not comply with the principals of cleanliness and simplicity. Many inventions, however ingenious at first sight they may appear, and however well they may answer experimentally, have to be discarded on

* See footnote, p. 76, and also p. 87.

account of unforseen circumstances which interfere with their efficient working in practice.

In conducting an examination into the sanitary condition of premises, a familiarity with the errors that are likely to be met with is hardly less important than a knowledge of what is right and proper, and it is essential that the enquiry should be conducted systematically, step by step; nothing being taken for granted, otherwise, sooner or later, a mistake will be made.

As traps are met with in connection with most appliances, it is convenient that they should first be discussed. The purposes served by traps, and the conditions with which all must comply, are subsequently detailed (see p. 94). The following are the common varieties met with in practice:-Syphon-trap, Gully-trap, D-trap, Bell-trap, Antill's trap, and Dipstone-trap. The two first-mentioned traps (or a modification of them) are the only ones admissible; all the others are more or less objectionable.

The simplest form of syphon-trap for use in the course of a drain is an ordinary pipe with a bend in it (Fig. 37); both

Fig. 37.

those represented in the drawing, however, are faulty for various reasons. The first because (1) the dip is not sufficient to provide a proper water-seal; (2) the bottom of the trap is rounded, consequently there is a risk of its being fixed out of the level; (3) there is no provision for the ventilation of the drain, in the shape of an inlet opening on the houseside of the water-seal; and (4) no means of access to admit of the trap or the drain beyond being cleared out, should either become obstructed, are provided.

The second is open to the same objections as far as the first and second points are concerned, and as regards the third, although means of access are provided, it is not at a point that will allow of ventilation, or the unstopping of the drain beyond. There is another objection to this, which is a form of trap sometimes met with, and that is that floating matters are likely to accumulate in the central shaft.

The trap which is best fitted for the purpose (Fig. 38), and

A

which is not open to any of the foregoing objections, has two openings, in addition to the inlet and outlet, one at A in the sketch, which is carried up by means of pipes to the surface of the ground, where it is covered by an open grating and thus acts as an air inlet, and the other beyond the seal, which may be used for cleaning the drain between the trap and the sewer or cesspool. It will be noticed that this trap has a deeper seal than the others; that the drain inlet is well above

Fig. 39.

the outlet, thus affording a better flush; and that it stands on a flat bottom, which facilitates its being laid level.

In the event of the drain terminating in a manhole, such as has been described on p. 84, previous to joining the sewer or cesspool, a special form of disconnecting trap, represented in the sketch (Fig. 36), with a raking-arm or by-pass to allow of the drain being cleared beyond the trap, should be used. In this case the inlet for ventilation is pro

vided by means of openings in the
manhole cover, or if, by reason of its
position, there is an objection to this,
by a special opening at the side, shown
by dotted lines, which is carried up

some distance above the ground level. SECTION AT A.
Fig. 39 represents an improved
trap introduced by the late Professor
Corfield; the syphon is egg-shaped

in section and curtailed in calibre ; SECTION AT B.
also, the raking-arm has a second
inlet which is sealed by a movable
plug with chain attached. This trap

more likely to be self-cleansing, but should it become obstructed,

as

Fig. 39.

may sometimes happen, the sewage which in consequence would collect in the manhole would be liberated by pulling the chain; without this contrivance it would be necessary to empty the manhole by means of a pump or with buckets before any one could enter it to unstop the trap.

The question of the necessity for trapping a drain before it

B.

joins the sewer is at present the subject of discussion among sanitary engineers. While some maintain that it is desirable to adhere to the practice hitherto observed, others advocate the free connection.

Undoubtedly the introduction of a trap in the course of a drain has the effect of interfering to a certain extent, with the free flow of the sewage, and tends occasionally to cause obstruction; therefore, if it can be shown that the practice is unnecessary it ought unquestionably to be discontinued.

By establishing a free communication between the drains and sewers, the various soil-pipe ventilators, and the ventilators placed at the top ends of drains, would act as outlets for sewer air, the inlets being the open manhole covers in the streets. By this means the circulation of air in the sewers would be encouraged, and one would hear less frequently of nuisances arising from street ventilators. On the other hand, the opponents of the new system say that the abolition of the trap establishes a connection, through the medium of the sewer, between the various houses of the town, and so exposes unnecessarily the occupants of one property to the consequences of the misdeeds or misfortunes of other people. For example, granting that enteric fever may be conveyed by sewer air, by omitting the trap at the junction with the sewer, the germs, in place of having a barrier imposed against their exit by other outlets than the sewer ventilators, are conducted along the drains to the houses where the gully-traps and the water-closet traps alone stand in the way of their entry into houses through the windows or water-closets, although, with free ventilation and efficient trapping, it is hardly likely that this would occur.

Probably the following is the safe conclusion to arrive at. Given a perfectly-sewered town, with thoroughly self-cleansing and ventilated sewers, and efficiently-trapped and ventilated drains, without any blind ends, it may be safe to abolish the intercepting trap. On the other hand, in the absence of these conditions, and they are seldom, if ever, met with, the wisdom of abolishing the trap may well be questioned.

In the case even of recently drained housed one not infrequently finds that a trap similar to that just described (Fig. 38) is placed at the point where the soil-pipe joins the drain, notwithstanding the fact that another and similar trap is quite properly placed at the terminal end of the drain. Under these circumstances, the soil-pipe cannot answer the purpose of a ventilator for the drain; consequently it is necessary to connect another ventilator with the drain beyond the needless soil-pipe trap,