required than the odd men or casual labourers, who are often set to do sewering. One of the risks to which sewers are liable is the breaking of pipes or cement joints by slight movements or sinkings of the ground, and it is well argued in favour of clay jointing that it will yield to such a movement and be as good as ever after it. I would rather say it will be as bad as ever after it; as liable to give way to any pressure from water within the pipes, and as liable to emit sewer gases from the pipes. 66 A most excellent plan for jointing pipes perfectly watertight, and yet so as to yield to slight settlements of the ground, is by Stanford's patent joints," of which I have samples here. These pipes have their ends and sockets fitted with collars of a bituminous substance, arranged to fit one within the other, and to form a sort of ball and socket joint, allowing of slight curving of the lines of pipes, or of slight settlements of the ground. By wiping these collars with an oily cloth before putting them together, they are slightly softened, and so make a watertight joint. They are especialy useful for rapid work, or in wet ground, where it would be difficult to make good cement joints; but even for ordinary work they would probably prove cheaper than cement jointing by their greater economy of time and by not requiring so much skilled labour. Where sewers have to pass over quicksand, or very soft ground, they should be encased in concrete, so as to keep them in true position. This can best be done by arranging the timbers used to support the sides of the sewer trench so that a continuous bed of concrete of about a foot thick may be laid below the sewer pipes. This concrete may be made of one part of blue lias lime, or other lime or cement that will set under water, to from four to eight parts of ballast and sand, this ballast consisting of broken bricks or stone, gravel, shingle, cinders, or other clean hard material broken to the size of hen's eggs or less, enough sharp sand being added to fill the chinks among the ballast, and the whole thoroughly mixed with only enough water to completely moisten it throughout. The concrete should be well pressed into the trench; the sewer may then be laid on the flat surface of the fresh concrete; more concrete should then be carefully packed under and around the pipes, so as to form with the under-bed one solid mass. In sewering through sinking ground over colliery workings, &c., it is sometimes needful to use strong cast iron pipes, with ball and socket joints, but usually Stanford's joints are strong and pliable enough. All syphon-traps, inlet grids and traps, access shafts, &c., in connection with tile pipe sewers should be supported on wide foundations of concrete, flags, or brickwork, and encased in concrete or brickwork to protect them from breakage or settlement. All sewer junctions should be curved like railway junctions, so as to lead the currents in the right directions without abrupt turns, which cause eddies and loss of speed. Where there is ample fall available, it is well to arrange slight drops or waterfalls in sewer manholes, or other convenient positions, as they tend to break up floating accumulations, and they also facilitate arrangements for flushing the sewers by moveable sluices or stops in the manholes. In order that sewers for ordinary house refuse may be selfcleansing, that is, not liable to silting up by gradual deposits of heavy or adhesive substances, the speed of flow through them must be not less than about 150 feet per minute, that is 13 miles per hour, and therefore it is positively requisite either to give the sewers sufficient fall to attain this speed of flow, or else to provide for cleansing them by frequent flushing, or other special means. Small sewers require more fall than large sewers in inverse proportion to their diameter, in order to give equal speed of flow. A thoroughly sound and simple rule for arranging the minimum falls for sewers may therefore be given thus-Let every 4-inch sewer have 4th inch fall per yard, every 6-inch sewer th inch, every 9-inch sewer th inch, and so on, but wherever the levels permit it, let every 4-inch sewer have 1th inch fall per foot, and so on. When sewers of any diameter thus arranged are running halffull or full, their speed of flow will be 144 feet per minute when the above falls are given per yard, and 250 feet per minute when the same falls are given per foot. But when running only onefourth full, the relative speeds would be reduced about one-fourth, and therefore it is best to make sewers as small as practicable for their work, so that the flow in them may be deep and rapid, instead of shallow and slow. In estimating the sewage flow from large numbers of houses, it is sufficient to provide for about five cubic feet per head of population per day, or rather, say, one cubic foot per head per hour to meet the busy times, and the rainfall discharge from urban districts may be estimated at 30 cubic feet per acre per minute during heavy rainfall. These two discharges -the sewage and the rainfall-should always be kept separate where practicable. As even the best and most rapidly flowing sewers become slightly coated with putrescible matter, and as their contents are more or less offensive and dangerous to health, the air or gases within all sewers should be rendered comparatively harmless by dilution with fresh air as much as practicable. When sewers are reasonably clean and are amply ventilated, the air from them is not very offensive or injurious; but grids in the roadways cannot, without serious nuisance and danger, be used to ventilate foul and dilapidated sewers, such as most of the old sewers in Manchester and Salford are, to the lasting disgrace of their Health Committees, who are content with pottering about the surface only. The Deansgate sewer is four or five feet in diameter, roughly cut in porous rock: a similar sewer branches into it from near the Old Town Hall. Market Street sewer is badly built of brickwork, and has several times broken in. Most of the minor sewers are of butt-jointed, pointed-oval pipes, thoroughly leaky. I believe that one chief reason why Manchester has remained for very many years in the lowest rank of health (as shown by the death-rate) among all the towns of England is because of the abominable sewers that permeate the whole place with their poisonous emanations. The public of Manchester should take every opportunity of backing-up their officials when they propose important sanitary improvements, instead of apparently preferring high deathrates to increased sewer-rates. The old sewers ought to be used only for surface water, and new watertight sewers should be constructed to collect all liquid refuse, and convey it rapidly and cheaply to the farm lands, where it could be usefully disposed of. Scores of towns in England have now successfully carried out this system, and many Royal Commissions, after examining the various chemical and other alternative processes, have declared the watercarriage system and the land irrigation system to be the only thoroughly efficient and reasonably economical plans for disposing of town sewage. I cannot in the present lecture spare time for more detailed reference to main sewering, but must now turn to the details of branch sewering, serving single dwellings or groups of dwellings. Every separate dwelling, or group of dwellings, should be only connected with the public main sewers through a syphon trap, which would check the passage of injurious gases or infective germs of disease from the public sewers into the private ones. Thus, each private group of branch sewers would be rendered only a possible means of spreading infection from within its own area, instead of from any place in the whole town. The most thoroughly effectual form of intercepting syphons and access manhole is shown in the accompanying section No. 1. The two syphon traps with ventilated open channel between them would effectually guard the house drains from emanations of the public sewers, even if the sewer gases were penned back by a flood or a rising tide. Nol. H C V A-Private sewer from the house or group of houses. (Sometimes several sewers may be thus brought into one manhole.) B-Inlet syphon-trap, cutting off the house sewer emanations from the manhole, and vice versa. C-Open space in manhole for separation of syphon-traps, and for access to them. D-Outlet syphon-trap, cutting off the public sewer emanations from the manhole. (For flushing the sewers a lid is put on to this syphon pipe, with a chain to the surface; water is run into the manhole to one foot depth or more, then suddenly let out by raising the pipe lid by the chain.) E-Outfall to public sewer. F-Ventilator to public sewer, carried up by an iron pipe. G-Ventilator to house sewer, carried up by an iron pipe. H-Iron lid to manhole, for ventilation and access; also forming a reserve vent between the public and private sewers. A very simple and cheap plan that is good enough for favourable circumstances is also shown in section No. 2. This one trap, with its narrow access shaft and ventilator, could only be completely trusted where the public sewers were reasonably good and well ventilated, but it is of great sanitary value in any case. N° 2. E A A-Private sewer from the house or group of houses. (Sometimes several sewers may be thus brought into one shaft.) B-Syphon-trap, cutting off the public sewer emanations from the private sewer. C-Outfall to public sewer. D-Ventilator to private sewer, carried up by an iron pipe. Every syphon trap should have an access shaft or manhole, for the purpose of removing the before-mentioned brushes, towels, cinders, and other insolubles which are occasionally found in sewers. With proper construction and due care a syphon will keep clear enough, I have seen several that had been buried for a score of years without getting out of order; but after digging down to place the syphon it is always worth while to retain an |