A, into the top of the long leg of the siphon, the air in this leg being at the same time expelled through the puff-pipe, B. The second trap, C, is of lead, and can be ventilated, if necessary, by the pipe D. Part of the flush is diverted to the flushing rim, in order to cleanse the basin. It is obviously a disadvantage, when only a small quantity of water is allowed by the water companies, that a great part of it should not pass through the basin, and various closets have been designed in which this objection has been overcome.

Doulton's siphonic closet (fig. 108) is on the same general lines as Jennings & Morley's, but with "the full discharge from cistern passing through and cleansing basin." The area of the water is 12 in. by 9 in., and the greatest depth 6 1/2 in. The depth of the trap-seal in the basin is 3 1/4 in. The bore of the outlet leg of the closet is 2 1/2 in., which is found to be sufficient for the passage of soil and paper. The joint between this and the lower trap is above the floor. It is claimed that the basin cannot be siphoned out by pouring slops or water into it.

Fig. 108. Doulton's Siphonic Closet.

The "Twycliffe" siphonic closet (fig. 109) does not require a second trap. The siphonic action is started in an ingenious but simple manner by taking part of the flushing water down the arm A and discharging it at B in the direction of the outlet-arm of the trap. The soil is therefore cleared out by the first part of the flush. The peculiar bends in the branch-pipe C are supplied with the closet, and are introduced to check the water until siphonic action is properly set up. These bends are in one piece of lead wiped to a brass socket at the top, so that the joint at the closet-outlet can be made with neat cement; or a brass screw-cone joint is made as shown at D; or a short lead tail piece is united to the outlet by a porcelain-metal wiped joint, to which tail-piece the lead bend can be united by an ordinary wiped joint. The area of the water in the basin is about 13 in. by 10 in., the greatest depth 7 1/2 in., and the depth of trap-seal 3 1/2 in. A flush of two gallons is sufficient to clear and recharge the basin, but in this, as in o»her siphonic closets, a 3-gallon flush is safer. The flushing-rim has a series of holes, instead of the usual continuous opening. The closet is also made with a central outlet at the floor-level, as shown by the dotted lines, but this cannot be recommended. A close imitation of the "Twycliffe" siphonic closet is also on the market. The basin is reversed, the bend of the trap being in front instead of the rear; by this arrangement the pottery tube leading to the nozzle at B can be made shorter and straighter, but the bend at the top of the trap is necessarily constricted; according to the published section, it measures at one point less than 1 1/2 in.

The "Injecta " siphonic closet (fig. 110) has a basin of almost normal wash-down form, but containing more water and having a deeper seal. As in the "Twycliffe" closet, siphonic action is started by a jet of water, but in this case the nozzle is at the back of the flushing rim and is directed into the standing water in the basin. A common disadvantage is that, if any soil adheres to the basin, it is removed by the flush, as the bulk of the water is discharged otherwise than on to the surface of the basin. The tailpiece B is a patented part of the apparatus, and is united to the pottery outlet of the closet by a special soldered joint. On one side of the tail-pipe a socket is formed for the puff or ventilation-pipe, which must be connected to the main ventilation-pipe. The depth of seal is 3 1/2 in.

Fig. 109. Twyfords' "Twyc'iffe" Siphonic Closet.

The "Barrhead" siphonic closet (fig. 111) has a water area measuring 13 1/2 in. by 11 in., and an 8-in. seal. The trap, which has a 3-in. bore, is of lead united to the basin by a special soldered joint. As in the last example, the siphonic action is started by a jet of water descending from the back of the flushing rim, and the long leg of the siphon has the bulbous portion with ventilation socket. In the section, the long leg of the siphon is shown behind the short leg, but in practice it is placed at the side in order to reduce the projection from the wall; this is correctly shown in the elevation. An objection to this basin is the shallowness of the water into which the soil drops; the curved part near the outlet joint is often fouled. The depth of seal is unnecessarily great, and precludes the use of a smaller flush than three gallons. The long leg of the siphon may be made sloping, like the tail of an open S-trap, so as to pass directly through the wall. The outlet is then connected into the side of the soil-pipe. All the joints, including those of the puff-pipe, are therefore outside the building, with the exception of the joint between the closet and trap, and this joint is under water.

Fig. 110. Shanks's "Injecta" Siphonic Closet.

In the case of closets in which siphonic action may be started by a pailful of slops or water, Dicksee's arrangement (fig. 112) is sometimes introduced. This is simply a small air-pipe connecting the long leg of the siphon and the flush-pipe, the flush-pipe being trapped below its connection with the air-pipe. When the siphonic action of the closet is started air is drawn from the flush-pipe, and this starts the siphonic action of the flushing cistern.

Shanks's "Barrhead " Siphonic Closet.

Siphonic closets have recently been made in bracket form to stand clear of the floor. The "Console Siphon" water-closet (fig. 113) is an example. It is on the lines of the "Twycliffe"; the bent outlet leg of the siphon is of brass. The basin has a 3-in. trap-seal, and requires a flush of three gallons. The total depth of the basin is only 12 in., so that there is a space of about 5 in. between it and the floor.

It is unnecessary to give further examples. All siphonic closets have a large water area and deep seal, and thus possess some of the chief advantages of valve-closets without their objectionable mechanism. It is essential that a siphonic closet should be fixed only in connection with the flushing apparatus which has been specially designed to suit it, as the satisfactory working of the closet depends to a very large extent on the nature of the flush. Many siphonic closets will not work satisfactorily with a flush of less than three gallons. It is also a great mistake to connect such closets to old soil-pipes, unless these can be proved to be of good design and workmanship; a long horizontal branch from the outlet leg of the closet to the soil-pipe may be sufficient to check seriously the siphonic action. Siphonic closets have been made to work with 1 1/2-in. regulating supply valves similar to those used for valve-closets, but valves of this kind can only be adopted in places where the water is supplied by meter or without restriction as to quantity, as, for example, as in the case of private supply. The long legs of the siphons are as a rule only 2 1/2 in. or 3 in. in diameter, and there is no reason why the soil-pipes for single closets should be any larger, unless the local Sanitary Authorities insist.