precipitated by some of them, while they increase the hardness of the river water, a matter of great importance if the stream be a small one.

"The manures that they produce are in every case very inferior, as may be expected from the known value of the sewage constituents which can be precipitated. They have all failed in producing valuable manure, because the valuable constituent of sewage par excellence is the ammonia, which of course invariably escapes in the effluent water and is lost to the manure; this shows the futility of all attempts to utilise sewage by precipitation alone."

Finally, there can be little doubt that the ultimate solution of the sewage problem is the utilisation of the sewage on land, either carrying it direct to the land, or in certain cases a combination of precipitation and irrigation by intermittent filtration.

SPECIAL SYSTEMS OF SEWERAGE.

(167) The Shone System.

In this system sewage is raised to the required height by means of compressed air. Its chief use is in towns which are unfavourably situated for disposal of the sewage by gravitation; it is in operation at Eastbourne, Wrexham, Southampton, Warrington, Henley and the Houses of Parliament, Westminster.

(168) The Liernur System.

This is in operation at Amsterdam and seems there to have given good results. Two separate sets of drains are required; the one is devoted exclusively to the evacuation of household waste water, rain water, and waste liquids from factories, these drains open into the canals. The second system of pipes receives the urine and sewage; the pipes are of small diameter (5 inch) and are connected with cylindrical iron reservoirs, in which a vacuum is maintained by means of powerful air vacuum pumps worked from a central station. The sewage is forcibly sucked into the reservoirs, hence the air from these small sewers never escapes into the house, any current set in motion being from the house to the reservoirs. The concentrated sewage thus obtained is dried and made into a poudrette, a valuable manure.

The Berlier system is in principle an exhaust pneumatic system very similar to the Liernur, it has been applied to a portion of Paris with great success.

(169) The Treatment of Sewage by Electrolysis.

This is the most recent method of treating sewage and is being carried on experimentally at Crossness. It is the invention of Mr. Webster, F.C.S. The sewage is electrolysed by flowing through long troughs, fitted at short intervals with large iron plates, the electricity being supplied by an Edison-Hopkinsondynamo of 25 horse power giving an output of 1,600 amperes and 20 volts; the quantity that such a dynamo can deal with is a million gallons a day.

The chlorides in the water are split up at the positive pole, the nascent chlorine and oxygen unite forming hypochlorous acid, which partly attacks the organic matter, and partly attacks the iron plate forming hypochlorite of iron; at the negative plate, potash, soda, magnesia, ammonia, &c., are set free. The ferrous hypochlorite formed at the positive pole is acted upon by the free bases, that is by ammonia, sodium, potassium and magnesium hydrate and thus decomposed; a precipitate of ferrous hydrated oxide is produced. The bubbles of gas, buoy the hydrated oxide of iron up for some little time, so that the first effect is the reverse of precipitation, the under liquid becoming clear while the surface is thick with scum. As the fluid flows on to a precipitating tank, the gases diffuse into the atmosphere and then the oxide of iron falls to the bottom carrying with it most of the organic matters. The effluent is a fair one, the sludge can be pressed through a filter press or otherwise used.

(170) Dry Systems of Sewage Disposal.

Dry conservancy requires examination by modern bacteriological methods, it is by no means certain that a great number of pathogenic bacteria are by this system not preserved, instead of destroyed, whereas we know from actual experiment that in water carriage systems numerous harmful bacteria are absolutely destroyed by soaking in water; for example the bacillus anthracis, when not in the spore state is rapidly disintegrated if placed in

water. Putting these unsolved questions on one side and presuming that no harm results from the preservation of deodorised excreta in the vicinity of dwellings for a longer or shorter period according to facilities for scavenging, it has been found to be fairly successful for small communities, as for instance at Wimbledon camp and in various schools and institutions.

The type of the dry earth system is Moule's earth closet, which is merely a wooden box with a pail beneath, a reservoir of dry earth above and a simple apparatus for measuring and applying the requisite quantity of dry earth. In the cheaper kinds of closet, the earth is thrown on the excreta by hand; in the dearer kinds, there is an automatic arrangement. The quantity of dry earth necessary to use each time is about 1 lb.

The suitability of various soils is in the following order: (1) rich garden mould; (2) peaty soils; (3) black cotton soils; (4) clays; (5) stiff clayey loams; (6) red ferruginous loams; (7) sandy loams; (8) sands. It will almost be necessary to provide some other means of disposing of the slop water, which will also contain a considerable portion of the urine. One of the best methods of disposing of the slop water of a village provided with earth closets is by sub-irrigation. That is, to convey the slop water to a suitable area, into drains as follows: common agricultural drains are laid 12 in. deep upon a bed of larger pipes divided longitudinally in half; the slop water escapes at intervals between the joints of the agricultural pipes and is absorbed by the earth, and serves as a fertilizer for vegetation. In many cases an automatic flush tank connected with the sub-irrigation area is necessary. In isolated communities and villages favourably situated, the slop water runs into open channels, into fields, or is received in streams, and so long as the latter are not used for drinking purposes and no nuisance is created, it is not wise to meddle with these primitive arrangements.

(171) The Pail System.

This is after all but a variety of dry conservancy. It is in use in many of the large northern and midland towns, either wholly or partially, such as e.g. Rochdale, Nottingham, Birmingham, Leeds, Halifax, Edinburgh, Nottingham, Manchester and Salford.

In some places, notably in Glasgow, the excreta are placed in a movable receptable without any absorbent material and carted.

away daily. The pail system in its best form involves some kind of absorbent material in the pail, for example in what is known as the "Goux System," called also "The Patent Absorbent Closet System" mixtures of any kind of vegetable and animal fibrous substances useless for other purposes are used as absorbents and these are mixed with a small proportion of iron or lime sulphate. These matters are pressed closely to the bottom and sides of the tub by means of a cylindrical mould which is afterwards withdrawn, leaving a cavity in the centre for the reception of the excreta. When these pails are emptied every two days, the results are good, but longer keeping usually exhausts the absorptive power.

A method of receiving urine into a mixture of salt and soot was exhibited in the Health Exhibition at Bolton in 1887, and received an award. This mixture certainly preserves to a remarkable degree urine and excrementitious matters generally, and the resulting mixture has a high manurial value. The trough latrines of Glasgow and Edinburgh Dr. Corfield considers as in effect the pail system adapted to large collections of people. This differs from the trough water-closets in not being connected with the sewers and requiring special scavenging arrangements for removal, A long fixed trough, slightly inclined towards one end, runs along under the seats of a row of closets; it is charged with only a small quantity of water and receives the total fluid and solid excrement. of those using it. In the Glasgow factories there is one of these latrines to about every 180 to 200 hands; the contents are emptied daily down a vertical pipe into a large closed tank placed close to the ground, from this tank the contents are transferred to a closed cart and removed.

(172) Water Closets.

The position of a water closet should be where possible at the back of the house, and if in structural connection with the house a short passage or lobby interposed, possessing facilities for cross ventilation. All modern houses are built this way, but occasionally in old houses, the closet will be found in the centre of the building. In such a case the author has ventilated the closet fairly satisfactorily by carrying a Tobin's tube into the closet, and running up from the ceiling a 4 in. zinc pipe to the roof, a continuous up draught being created by a small jet of gas burning beneath the opening of the shaft.

There are three main types of water-closets, viz.: the pan watercloset, the valve closet, and the hopper closet. The pan closet is perhaps the most common form, and taking it all in all the most insanitary. The closet pan is closed, see Fig. 41 at the lower end by a sort of deep saucer which always contains a little water, and can be made to swing downwards by pulling the handle of a lever to which it is connected; the cavity in which it swings is called a container and is usually made of iron, from the container the closet contents pass into a trap. The result of this arrangement is that the container gets soiled with offensive matter and cannot be

Z G

FIG. 41.

FIG. 42.

cleaned and is in effect a reservoir of foul air, the trap is also one of the worst forms, and gets coated with excretal matters and often corroded by gases and liquids; it is likewise a smaller foul air reservoir. From these foul air reservoirs fœtid gas bubbles up and escapes whenever the closet is used. The original valve closet was the "Bramah." The lowest part of the basin is closed with a tightfitting valve moving in a valve box, the box only being just large enough to allow of this movement, below the valve box is a syphon. To such closets there is an overflow pipe from the closet pan to prevent the accidental overflow of the flushing water over the edge of the basin (see Fig. 42). The overflow pipe as a rule passes into the valve box, and has a syphon bend. There is however some difficulty in keeping this overflow pipe properly trapped, and there have been