at its lower part with a trap-preferably a siphon trap, or an anti-D trap formed of 4-inch lead pipe-and the outlet of this trap is connected with the soil pipe. The valve closet should be flushed from a small cistern holding 6 or 8 gallons of water, and not from a water-waste preventer, as it is necessary to provide a considerable after-flush"-that is to say, to allow a supply of water to enter the basin after the handle is released and the valve closed.

To secure an after-flush, some form of regulator" valve in the supply pipe from the cistern to the closet basin must be used. The "bellows regulator," which is commonly used, consists of a piston working in a cylinder, and connected with the handle of the closet and with the valve in the supply pipe. The cylinder is provided with an escape pipe for air, on which is a tap to regulate the speed with which the air escapes and the piston falls. When the handle is raised, the valve in the supply pipe is opened, and the piston also is raised; but on letting go the handle the clack valve to the closet basin being then closed -the valve on the supply pipe is kept open, admitting water to the basin, until the piston has completely fallen and thereby closed it. The amount of after-flush, which is directly proportional to the slowness with which the piston sinks in the cylinder, can be regulated to a nicety by the tap on the airescape pipe.

As the outlet to the closet basin is guarded by a water-tight valve, the basin may overflow from too much after-flush, or from the throwing in of slops. It is necessary, therefore, to provide an overflow pipe to the basin; this is usually carried from near the top of the basin into the valve box below, after forming an bend, which by holding water prevents the ascent of foul air from the valve box. But it is found in practice that foul matters may find their way into or accumulate in the overflow pipe, and that the water in the bend is liable to be evaporated or drawn out by siphonage when the contents of the basin are discharged through the valve box.

Two precautions are adopted to obviate this difficulty. The first is to carry the overflow pipe into that side of the valve box where its open end will be protected by the depressed valve; and the second, which is most necessary, is to recharge the water in the overflow at each use of the closet. The basin of the closet should be provided with a flushing rim. Occasionally a

ventilating or "puff" pipe is attached to the valve box, and carried up and out into the open air, being left with an open end away from any windows. When the contents of the basin. are being discharged, the foul air in the valve box then escapes into the open air, instead of into the closet compartment.

There is very little risk of the deposition of filth in any part of the apparatus, as the large volume of water which the basin. can contain effectually flushes the small valve box and trap beneath. Occasionally the valve box is enamelled inside to prevent corrosion. The chief disadvantage of the closet is that the clack valve may become in time leaky, allowing the water in the basin to escape, and possibly foul air to ascend into the general air of the closet.

Wherever a valve closet is used as a urinal or for the reception of chamber slops, a white ware slop-top should be fitted, and the seat should be hinged for lifting. Valve closets are also now made in pedestal form, so as to obviate the wooden casing and riser. An advantage possessed by valve closets over the wash-down closets is that the flushing is comparatively noiseless; and this fact accounts for their popularity in the best class of residential property.

In the anti-D trap the calibre of the pipe is diminished in the bent portion which holds the trapping water, and the bend of the pipe beyond the trap instead of being circular is squared. These properties cause some resistance to the passage of water through the trap, and tend to prevent both siphonage by suction -i.e., the drawing of the water in the trap by the passage of water down the soil pipe from a higher level-and siphonage by momentum, which may occur in plain siphon traps by the water discharged from the water-closet sweeping through the trap, insufficient remaining behind to form the water-seal. The depth of the water-seal in water-closet traps should not be less than I inch, and not greater than 1 inches. If the depth of the waterseal is too small, there is a liability for the trap to be unsealed; if the seal is too great, the trap and the closet above it are not self-cleansing with an ordinary flush of water. These remarks apply more especially to "wash-down" closets (short hoppers) with water-waste preventers.

The Water-seal of Traps.-The water-seal of a trap is the vertical distance between the level at which water stands when the trap is fixed in position, and the lowest point of the bend of the upper surface of the trap. Thus in

figs. 20 and 21, which are diagrammatic sections of a S trap and a P trap, in each case the water-seal is the same, namely the vertical distance AB in the case of the S trap, and the vertical distance A'B' in the case of the P trap. The water-seal is, in fact, the depth of water that opposes the passage of air or gases from one side of the trap to the other, from outlet to inlet or from inlet to outlet. In the figures, the upper dotted line represents the water

FIG. 20. S trap, with Water Seal. FIG. 21.-P trap, with Water Seal.

level in each trap, and the lower dotted line is parallel with the upper dotted line, and is tangential to the apices of the bends.

In the plug closet the basin and trap are usually cast in one piece of china or stoneware, the basin above being shut off from the trap (siphon) below by a solid plug or plunger, by which water is retained in the basin. The cistern and flushing arrangements may be the same as those for the valve closet, an afterflush being necessary for both alike. The plug, which is connected directly with the handle, is usually perforated by a channel bent on itself so as to form a trap, and thus provides an overflow to the basin, permitting water to pass through the plug to the trap beneath. Sometimes these closets are used without the trap beneath, but in both plug and valve closets a siphon trap is necessary to prevent the passage of foul air from the soil pipe when the closet is discharging its contents. The plug or plunger is liable to become much soiled, and, being out of sight, escapes cleaning. When this is so, it may happen that excremental filth is forced up on the handle when the plug is suddenly plunged. This constitutes a great disadvantage in use, and has led to the practical abandonment of plug closets. The valve and plug closets are under the disadvantage of having a space between the water in the basin and the water in the trap, from which air-possibly foul-escapes into the general air of the closet when the contents of the basin are being discharged. But they have this advantage over those of the first class, that the larger quantity of water in the basin renders. them more cleanly in use.

On the floor beneath the closet basin is usually placed a lead safe-tray, to catch any overflow. This tray should be provided

with a waste pipe, which must be carried through the wall into the outer air, its end being covered by a brass flapper to prevent cold currents of air passing into the house. It was formerly the custom to connect this waste pipe with the D trap (see fig. 18) under the closet basin, thereby permitting foul air to enter the house at all times.

Water-closets should be placed against the outside wall of a building, in which is a window with an area of at least 2 square feet, made to open, and reaching to the ceiling. Where possible they should be separated from the house by a well-ventilated lobby; for it is important that air from the closet should find an easy exit to the outer air, and not pass into the house, as so often happens when water-closets are placed in dark, unventilated corners. The water-closet must not open directly into any

FIG. 22.-Trough Water-closet.

living-room, factory, workshop or compartment in which food is stored. The division wall between the water-closet and a dwelling-room, or a factory, or workshop, or food store, should always be of brick, and not a porous lath and plaster structure.

The trough closet is used in large establishments, as hospitals, schools, workhouses, and asylums. One apparatus serves for the use of several people at the same time, and the flushing can be rendered automatic. The old form of closet (fig. 22) consists of an open trough, usually of stoneware, with rounded bottom, of varying length according to the number of compartments desired. The trough has a slight incline towards the drain; and by means of a weir at its lower end it is able to retain sufficient water to cover the bottom for its whole length. It terminates in a siphon trap protected by a grid, to keep back articles improperly thrown in, before joining the

drain. Each seat over the trough should be in a separate compartment. The closet may be flushed by means of a Field's annular siphon flush tank (see fig. 13) of capacity proportional to the length of the trough to be flushed.

The more modern and approved type of trough w.c. or latrine, is a great improvement upon the old form. In this (fig. 23) the

trough is retained, but each closet is cut off from its neighbours by a separate basin, the outlet from which dips into the water in the trough. The trough, moreover, is kept filled with water, which also rises up for a few inches into each w.c. basin; this is effected by doing away with the weir and substituting a high siphon trap at the outlet to the trough. Each separate basin