or ten times as great as that of the fæces, consequently the total urine is worth about six times as much as the total fæces. The total Nitrogen voided annually by an individual of a mixed population is taken as being equivalent to 10 lb of ammonia, worth 6s. 8d. Higher values have been given by various authorities, but it is better to take the lower estimated value, especially as it was stated by the late Dr. Voelcker that nitrogenous organic matters (in which form the nitrogen of sewage principally exists) is worth considerably less than ready made ammoniacal salts. The value of potash is 2d. per ib, and of phosphate of lime 1d. per fb, but the amounts of these constituents in the excreta are very small.

The estimated or theoretical money value, then, of the excretal refuse of an individual of a mixed population for one year, may be taken as being from 6s. 8d. to 7s. It is very evident that it must be impossible to realize practically any such value, because it is impossible to collect the whole of the urine and fæces pure, i.e., unmixed with other substances, which greatly detract from the value because they are agriculturally worthless.

Fæces and urine, especially when mixed, as in cesspools, privies, and sewers, rapidly undergo putrefactive changes, giving rise to the formation of fœtid gases (organic vapours, ammonium sulphide, etc.). The urea (CO (NH)) of the urine decomposes, giving rise to carbonate of ammonia; and so rapid is this change, that it is probable that even in the best sewered town, all the urea of the urine in the sewage has been converted into ammonia before the arrival of the sewage at the outfall.

House waste waters. In these are included the waste waters from kitchens, which are highly charged with decomposable organic matters and grease, and slop

waters containing urine, soap, the dirt from the surface of the body and from clothes. These waste waters, when mixed with the liquid refuse or drainage of stables, cowsheds, and slaughter-houses, with the washings from the street surfaces, with the urine from public urinals, and with the waste liquors from manufactories, form the sewage of the non-water-closeted or midden towns. The drainage from stables is very rich in urine (one horse excretes about 15 times as much urine as an adult man); and the waste liquors from manufactories are often excessively foul."

It is not surprising then to find that such sewage is but little less foul than that of water-closeted towns, which contains the solid human excreta as well. The putrescible organic matter in suspension is greater in midden than in water-closet sewage, whilst the organic matter in solution is but slightly less in the former than in the latter. The Rivers Pollution Commissioners stated in their First Report, that "for agricultural purposes, 10 tons of average water-closet sewage, may, in round numbers, be taken to be equal to 12 tons of average privy sewage," ie., sewage of privy towns, where human fæcal matters are kept out of the sewers. Such being the case, it is necessary to bear in mind, that in towns where there are middens or some form of dry closet for the collection of fæcal matters, there is also a liquid sewage to be conveyed away from the houses by drains and from the town by sewers, which is too impure to be admitted into a stream, and which must therefore be purified before being so discharged.

• The waste liquor from flannel washing is said to contain twenty times more valuable manurial constituents than London sewage, Rivers Pollution Commission, 3rd Report.

CONSERVANCY SYSTEMS.

Middens.-The system which formerly prevailed in many towns in this country-where there was any system at all-was that of privies, midden-pits, and cesspools, often open to the air and unprotected from rain, and situated in the yards and areas about houses. These receptacles were generally mere holes dug in the ground; and their contents overflowed, saturating the air with noxious effluvia, or percolated into the soil around the houses, and poisoned the water in the neighbouring wells.

At the present time, in those towns which still retain conservancy systems, the middens are required to be constructed according to certain definite rules. The model bye-laws of the Local Government Board with regard to the construction and management of privies and middens require that:-the privy must be at least 6 feet away from any dwelling, and 40 or 50 feet away from any well, spring, or stream; means of access must be provided for the scavenger, so that the filth need not be carried through a dwelling; the privy must be roofed to keep out rain, and provided with ventilating openings as near the top as practicable; that part of the floor of the privy which is not under the seat, must be not less than 6 inches above the level of the adjoining ground, must be flagged or paved with hard tiles, and must have an inclination towards the door of the privy of half an inch to the foot; the capacity of the receptacle under the seat of the privy must not exceed 8 cubic feet-a weekly removal is then necessary; the floor of this receptacle must be in every part at least 3

• See Corfield's Treatment and Utilisation of Sewage, 3rd edition.

inches above the level of the adjoining ground; the sides and floor of this receptacle must be constructed of impermeable materials-they may be flagged or asphalted, or constructed of 9-inch brickwork rendered in cement; the seat must be hinged, or other means of access to the contents of the privy must be provided; and the receptacle must not communicate with any drain

or sewer.

With middens constructed and managed according to these rules, there would be no danger of percolation of liquid filth into the soil around houses and in the neighbourhood of wells; and there would not be much pollution of the air from the excreta-except during removal-if their dryness was ensured by the proper application to them of ashes and cinders. The success of the system depends to a large extent on efficient inspection by the nuisance inspector, and on proper scavenging arrangements.

Cesspools. These receptacles for filth are so evidently undesirable in the neighbourhood of houses, that it is the practice now in nearly all towns to fill them in and provide more suitable means for the collection of excreta. Until the repeal, in 1815, of the law which prohibited the passage of sewage from houses into the sewers, nearly every large house in a town had a cesspool on the premises, often of enormous size and situated in the basement. When, in the year 1847, it became compulsory to drain houses into sewers, many of these cesspools were filled up or otherwise abolished; but many of them escaped observation, and to the present day it is no unusual thing to find one or more cesspools in the basements of town houses, of whose existence the owners or occupiers are profoundly ignorant.

In country districts where there are no sewers, cesspools are still largely used for the reception of all the house refuse. If dug in a porous soil, such as gravel or chalk, they are too frequently constructed to allow all the liquid filth to percolate through their walls into the soil, with the almost certain danger of polluting wells, springs, and other sources of underground water supply. When the liquids escape thus easily, the cesspool but very rarely requires emptying, and this fact constitutes the raison d'être of the porous cesspool.

The model bye-laws of the Local Government Board require that the cesspool must be at least 50 feet away from a dwelling, and 60 to 80 feet distant from a well, spring, or stream. It must have no communication with a drain or sewer (in sewered districts), its walls and floor must be constructed of good brickwork in cement, rendered inside with cement, and with a backing of at least 9 inches of well puddled clay around and beneath the brickwork. The top of the cesspool must be arched over and means of ventilation provided.

Constructed in accordance with these rules, the possible dangers of cesspools are reduced to a minimum. The principle, however, which is bad, remains the same: for it is not desirable to retain in any receptacle, however well constructed, a large collection of solid and liquid excretal refuse, there to undergo putrefaction with the formation of offensive gases.

In this country cesspools are generally emptied by hand labour—a disgusting and dangerous task, or by pumping into a night-soil cart. On the continent, and especially in Paris-where nearly every house has its "fosse permanente" in the courtyard-the cesspools are emptied by pneumatic pressure. A flexible tube, connected with a tub or "tonneau" exhausted of air by an