material is done by means of washing and riddling, the broken pieces being thrown into water, and then lifted out again with a wide pronged fork.

This method is put forward by Mr. Stoddart as being greatly preferable to the ordinary riddling, in that it removes all the fine clinker adhering to the larger lumps.

At Knowle (Bristol) another of Stoddart's patent distributors is used. It deals with a septic tank liquor, with efficient results in many ways, though by no means perfectly. The trays there are well sheltered. In many respects, however, the conditions are not considered ideal for a fair test of the apparatus.

The resulting effluents are of a high class, bacteriologically and chemically, apart from the organic solids in suspension.

The Stoddart distributor (Fig. 16A) consists of a gutter provided along the bottom on the under-side with a series of drip-points. On filling with liquid, the latter overflows the margins of the gutter, and on reaching the nearest drippoint falls upon the surface of the filter in a succession of drops.

The gutter is made V-shaped in section, partly to secure the maximum of rigidity, partly to direct the liquid towards the drip-points. Several distributor gutters are conveniently united together to form a distributor sheet, provision being made for the passage of the liquid from the upper to the under surface by a number of openings between the gutter.

These openings may be of any size, as they do not determine the comminution of the liquid, this being effected by the drip-points.

The distributors are connected with the sewage tank by means of specially-designed cast-iron channels (supply channels), provided with recesses to form water-tight joints with the end of the distributor, and the whole apparatus is supported by adjustable chairs carried on iron tees, by which means levelling is readily effected.

When the system of channels and distributors is in action, the liquid should stand at one uniform depth throughout, whatever quantity of liquid is being applied, and the exit. it is claimed, is so free and unimpeded that it is immediately disposed of.

Hence, as it is considered, the distribution is completely independent of variations in the rate of flow, the only, difference observable being in the rapidity of the dropping. Moreover, as the comminution of the liquid is effected in the

B

interval between the margins of the distributor gutters and the drip-points below (scarcely more than one inch), practically the whole of the fall is utilised in the filter body.

The members of the Fifth Royal Commission report that "In ordinary cold weather and frost the working of the Stoddart filter is not affected, except in so far as there is a slight lowering in the temperature of the effluent. The distribution at Horfield has been uniformly efficient during our observation, though not perfect.'

Aerating Trays.

At Caterham Barracks, the depôt of the Foot Guards, there are four "Aerating Trays," as the filters are called, each 11 feet by 9 feet 6 inches, an area of 231 square yards, a total area of 93 square yards, and a 5-feet depth of material (coke). The sewage is an exceptionally strong domestic one from some 1,300 men, and is first treated by septic tank, and what is called by Mr. Scott-Moncrieff, its inventor, a "Cultivation Tank, 42 feet by 20 feet, by about 8 feet in depth, in which the filtering material is flint.

The effluent from a closed septic tank is received into the cultivation tank by means of a large perforated pipe from the primary tank, and enters the cultivation tank underneath the flints, and is discharged from it in a highly-septicised condition through three outlets near its surface.

The aerating trays are arranged in the form of four filters, each consisting of seven concrete trays, perforated at the bottom and filled with coke. The coke is graded from three-eighths of an inch in diameter in the uppermost tray to about three inches diameter in the lower ones.

The distribution of tank liquor is effected by the tipping of four troughs, which each discharge about fifteen gallons of liquid into perforated pipes extending over the surface of the material.

At the ordinary rate of flow the discharges take place about once in twenty minutes. If the distributing pipes are kept clean, the method is very effective; but they need constant attention, and require to be brushed and picked out at least twice a week when the flow is at the normal rate.

The total time which is spent in cleaning the primary tank and the pipes each week is about twelve or fourteen hours for one man. During this time the filters are out of work, and the whole of the tank liquor goes to the land.

The filters themselves need little attention, the uppermost trays requiring only occasional raking; the lower ones are not touched.

Some Rotating Distributors Described.

Fig. 17 illustrates a Scott-Moncrieff Rotating Distributor on a quarter-acre bed, similar to those in use at the works of the Birmingham, Tame, and Rea District Drainage Board. The apparatus shown is driven by its own oil motor, which renders it quite independent of the "head" or volume of the sewage effluent. The bed has a vertical stand-pipe in the centre, into which the effluent from the tank flows; a horizontal arm attached thereto is capable of being revolved about the centre. Fig. 17a will help to explain this. The revolving arm consists of a large main trough or carrier, into which the sewage is delivered from the vertical stand-pipe just alluded to. This arm is quite close to the surface of the filter-bed, thus preventing any sewage spray from being blown about by the wind.

The distributor is so constructed that the same amount of sewage can be discharged in a given time over each square yard of the filter-bed, and by this means no portion of the bed is under- or over-worked; thus the rate of discharge (that is to say, the daily amount of effluent poured on to the bed) can be regulated. Intermittent aeration is also provided for. By whatever system sewage is treated, if it requires subsequent filtration through "beds," this distributor can be employed, and it can be constructed to suit any shaped filter.

At Accrington, fourteen filters are in use to deal with the septicised sewage of some 46,300 persons in open tanks. The majority of the population is served by water-closets constructed on what is called the "Waste water system," in which the closets are flushed with slop water, and in wet weather also by water from the back roofs of the houses.

A considerable portion of the population is still served by the pail system, there being something like 2,000 pails, and as the contents of these are tipped into a tank at the depôt, which is flushed into the sewers twice a day, they may be looked upon as having much the same effect on the sewage as water-closets.

These are all circular "trickling" filter-beds, having a diameter of 49 feet 9 inches, a depth of 8 feet, and a cubic content of 588 cubic yards. The filtering material is either coke, ranging from 2 inches to 4 inches in diameter, or clinker of the same diameter.

The construction of the filters is simple, the material being built up on a false bottom, consisting of large semi-circular

Fig. 17. Scott-Moncrieff's Effluent Distributor.