2. Taylor's dry Closet.—In this closet the fæces and urine are separated by means of a revolving disc, which is worked by a lever in connection with the closet-seat. When the lid of the seat is lifted the disc moves slightly round, and when it is closed a small quantity of ashes, or of ashes mixed with disinfecting powder, is thrown from a hopper upon the soil. The solids are retained on the disc until a complete revolution is made; by which time they are usually almost dry, and are then scraped off by a knife into a receptacle beneath. The whole apparatus is thus made self-acting in connection with the opening and closing of the lid, and each time the closet is used a certain portion of the soil which has been longest exposed on the disc is removed. The urine runs off into a neighbouring drain, ditch, or tank.

The apparatus is more costly than the common earth-closet, and the disc gets very much soiled, and requires to be frequently cleaned;-in other respects the plan has been well spoken of.

3. Various other modifications of the dry method have been tried or proposed, among which may be mentioned the Carbon Disinfecting and Deodorising Closet of Messrs. Weare and Co., in use in several parts of Liverpool; the employment of charcoal from seaweed, and of carbonised excreta instead of earth as proposed by Mr. Stanford; and carbonising the excreta in retorts and using the charcoal thus obtained as a deodoriser for fresh excreta, as proposed by Mr. Hickey. All of them, however, are more or less open to the objections which have been urged against the earth-closet system, and do not meet the requirements of large communities.

SECTION IV.-REMOVAL BY WATER.

This is the only system suited for large towns. The same channels which are required for the removal of the waste water, may also, if properly constructed, be used for the removal of sewage, and not only so, but the waste water can be utilised as a very efficient vehicle for the conveyance of the excreta. In most cases the subsoil water, surface water, and the water used for domestic purposes, are all eventually discharged by the same channels, so that the drainage and sewerage of a town usually form part of the same system.

1. Drains and Sewers.In any system of drainage, whether for towns or country districts, it is necessary that the drainage channels should have sufficient area and declivity to maintain the discharge of the water which they receive at all times, and at its fullest flow. This quantity will of course depend chiefly on the rainfall of the locality to be drained, and upon the amount entering the drains from other sources. Thus, in country districts, the water to be carried off may be partly derived from porous strata, which have their gathering ground beyond the boundary ridges of the drainage-area; and in towns, the water-supply artificially brought in is added to the amount derived from the drainage of the inhabited district. Moreover, as the soil acts as a kind of reservoir, the water does not enter the drains in the open country as rapidly as it falls, indeed a considerable portion of it is evaporated or absorbed by vegetation; but in towns it runs off the roofs and paved or macadamised surfaces almost as fast as it is delivered.

Guided by these considerations, engineers have estimated that the capacity and declivity of the water

channels for country districts should be sufficient to carry off the greatest available rainfall occurring during twenty-four hours in that space of time, whereas in towns they should be capable of discharging the greatest hourly rainfall on the area, and the greatest hourly supply from other sources. The depth of the greatest hourly rainfall is estimated by different authorities at from half-an-inch to an inch.

In small towns, where the storm-water, or greatest hourly rainfall, may be passed over the surface without causing injury, the main sewers need not be constructed of a capacity to discharge it, a plan which has been carried out at Penzance and Carlisle. In other towns again, as at Dover, Ely, Rugby, etc., the storm-water is carried off by the old drain-sewers, and the sewage by separate pipe-sewers; or pipe-sewers are used exclusively for the sewage, and separate brick drains are constructed for the subsoil and storm-waters.

The advantages of the pipe-sewer system are, that the pipes are strong, and, if well jointed, prevent percolation; that they can be quickly laid, and require much less excavation than brick sewers; that they can be made of various curves to suit different positions ; and that, with a proper declivity, they are not liable to get fouled. Another great advantage depends on the fact that the sewage can be treated without dilution, and when a pumping-station is required at the outfall, the original cost and working expenses are much lessened. On the other hand, the pipe system does not ensure the important hygienic condition of drying the subsoil if separate drains are not laid down. Drain-sewers, however, as they are usually constructed, do act efficiently as subsoil drains, and, unless the town is flat and low

lying, or where there is any chance of the backing up of sewage from the outfall, as at Cambridge, there is little risk of percolation.

(1.) Construction of Drain-Sewers.—The main drains or sewers of a town are underground arched conduits, built of brick in cement, so as to be perfectly watertight. They are generally laid on a bed of concrete, to prevent sinking of any part of the track, and consequent fracture. The cross-section preferred for them is an egg-shaped oval with the small end downwards, and with a width of at least 2 feet, to allow men to enter them for the purposes of cleansing and repair. They should be laid out in straight lines and true gradients from point to point, so that the current shall have a velocity of not less than 1 foot, and not more than 41 feet, per second. At each principal change of line or gradient, arrangements should be made for inspection, flushing, and ventilation; and at all junctions or curves the declivity should be increased, to compensate for friction. No sewers or drains should join at right angles, or directly opposite the entrance of others. Tributary sewers should deliver in the direction of the main flow, and should also have a fall into the main at least equal to the difference between their diameters.

Surface-drains or gutters communicate with the underground drains by gulley-holes, which are covered with gratings, and generally fitted with syphon-traps to prevent the escape of foul air. Branch drains, leading from the houses and from the adjoining ground, are usually made of earthenware pipes, bedded on concrete and well jointed in hydraulic mortar or cement. They should never be less than 4 inches in diameter, and should have a declivity sufficient to ensure a velocity

of flow of at least 4 feet per second, to prevent the formation of deposits. All junctions with other drains or sewers should be curved or acute-angled, and, whenever practicable, they should be made in a vertical or transversely inclined, instead of a nearly horizontal, plane. Pipes of small size should always be joined on to pipes of larger size, as 4-inch pipes into 6, 6 into 9, and 9 into 12.

No drain should ever commence in the basement of a house, otherwise the updraught produced by the increased inside temperature will occasionally draw the air through any trap. Sink-pipes, and pipes from cisterns, lavatories, or baths, should all communicate with the drains outside the building, and at each point of connection (although it is preferable that there should be no direct connection) there should be a trap with an opening on the other side for ventilation. Soil-pipes should be carried up to the roof of the house, and no other pipes should open into them. (See Chapter on Dwellings.)

(2.) Ventilation of Sewers.-In order to prevent concentration or stagnation of the gases which are largely given off by sewage, it becomes a matter of the utmost importance to provide numerous openings communicating with the sewers to ensure free ventilation. Main sewers, with steep gradients, should have a manhole, a tumbling bay, and double ventilating arrangement, at intervals of not less than 300 yards. The tumbling bay or fall is provided to allow of a flapvalve being applied to the discharging end of the sewer, and thus compel the gases to ascend through the ventilating shaft. One or more charcoal baskets are placed in the manhole to deodorise the sewer-air as

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