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some other means than sewers, then it might become a matter for consideration whether the necessity for the removal of excreta alone would warrant their introduction, but as sewers must exist for ordinary waste water purposes, the only point to determine is whether the addition of excreta is expedient or not. Now, so far as the composition of the sewage of water-closet towns is concerned, as compared with that of towns in which the dry method is in operation, the difference, as already pointed out, is very little, but the volume in the one case as compared with the other is considerably greater. Six gallons per head per day increase of volume in the case of water-closet towns (Parkes) makes a considerable difference in the sum total of sewage that has to be disposed of; and in the case of inland towns, particularly where the absence of sufficient fall necessitates the pumping of every gallon, for the purpose of land or other treatment, before it is discharged into a stream, such an addition
may become a matter for serious consideration. Then, again, it may be that the water-supply is limited, and cannot bé supplemented without considerable expenditure, in which case the
saving of 6 gallons per head per day must not be overlooked.*
To obviate these objections, various plans for utilising the ordinary house waste-water as a flush for water-closets havo recently been devised, and some town authorities are endeavouring to overcome the difficulty in this way by methods which will be described in the next chapter.
There can be but little question that the water-carriage system is the cleanest, most rapid, most convenient, and cheapest method of sewage removal.
The dry system, or the conservancy system as it is termed, has been adopted in many towns, but, even where carried out on the most approved principles, it must necessarily give rise to nuisances in densely populated areas. On the ground of expense, also, it is found to be a mistake, and were it not on account of the outlay that has been incurred, it is probable that most authorities who have adopted the system would abandon it. It is only in scattered rural districts where there is land enough attached to each house, on which the excrement can be disposed of, that the system is at all admissible; the difficulty in dealing with the excreta in populous districts necessitates an annual expenditure which is not by any means recouped by the sale of the manure. The mistaken idea that the introduction of ordinary water-closets into districts greatly increases the difficulty of treatment, is probably answer
The estimate of 6 gallons is, probably, in excess of the actual figure.
able in most cases for the adoption of the conservancy method of sewage removal, and the sooner the true state of the case is understood by authorities the better.
Privy-middens ought undoubtedly to be abolished, particularly in populous districts, and if excrement is permitted to remain on the premises, it must be under conditions least harmful to health. The earth-closet, if the necessary labour can be provided, is perhaps the best dry system of removal, but the trouble entailed in attending to essential details is too great to admit of its adoption, except in better-class houses and schools. The pail system, with frequent and regular removal, may perhaps be permitted, but it would be well if authorities of populous districts would come to the determination to encourage the substitution of water-closets for all insanitary privies, and insist upon their introduction in the case of new houses.
The term separate system is applied to a water-carriage system in which separate channels are provided for the rainfall. The addition of surface water to the sewage of inland towns greatly taxes the efficiency of all methods of sewage treatment, and although it may be useful as a flush for sewers, it is too irregular and uncertain to be admissible in cases in which flushing is specially necessary.
Towns without a proper system of sewers are to be congratu. lated as regards this point, for they are in a position of being able to make use of what sewers exist as storm-water carriers, and to start de novo to construct sewers on the separate system.
SEWERS AS A DANGER TO HEALTH. One often hears it stated that certain towns were perfectly healthy, and experienced no nuisance from the disposal of their sewage, until the introduction of a general system of sewers. Such a statement must be received with a considerable amount of qualification, although it contains an element of truth. Many examples of the old order of things are to be found even now in small towns, where the fluid refuse is simply discharged from the houses on to open channels communicating with street gutters along which it travels to the nearest ditch or stream; although sometimes it is conveyed there in brick sewers with which the street gutters are connected, the whole being periodically flushed with storm water. Now, no doubt, such a system is extremely unsightly, and the risk of well-pollution and other dangers, from the saturation of the soil with sewage which percolates freely from numerous stagnant pools along the course of the rude channels, is great; but that there is perfect "disconnection” and free “ventilation " there is no question, and, when compared with an arrangement which connects each house direct with an unventilated and possibly badly-constructed sewer, it is certainly to be preferred, especially if the people are not dependent upon local wells for their water-supply. This, however, is no longer a true comparison ; we now appreciate the importance of flushing, trapping, disconnecting, and ventilating our drains and sewers. The only instances (three out of twenty-four), in Dr. Buchanan's enquiry (p. 4), in which the deaths from enteric (typhoid) fever had increased since the introduction of sewers, &c., occurred in towns where, undoubtebly, the sewage arrangements were imperfectly carried out. In the case of the other twenty-one towns, an average reduction of 45.4 per cento took place.
OONSTRUCTION OF DRAINS AND SEWERS.
Drains and sewers must be so constructed as to comply, in every respect, with the principle of immediate and perfect sewage removal. There is considerable confusion with regard to what is a drain and what a sewer. Shortly, the definition, as laid down by the Public Health Act, is that a
66 drain” is a channel which receives the drainage of one building or set of premises within the same curtilage, and a "sewer,” that which receives the drainage of two or more buildings or premises (see Appendix).
Drains and sewers should be water-tight, smooth in the interior, and not larger than is necessary; they should, if possible, follow a straight course and have a sufficient fall, varying in accordance with the diameter, and, as far as possible, of the same uniform rate; where curves are unavoidable, they should not be abrupt, or better still, at such points, and where tributaries join, manholes should be provided. Ample provision should exist for ventilation, so that sewer gas may not stagnate but have free outlet into the open air. There ought to be no direct connection between drains and sewers, but a trap should be inserted near the junction of the one with the other, with an air inlet on the house side. *
* Some sanitary engineers now advocate the direct connection with gewers, without the intervention of a trap, of all house drains, in which case the soil-pipe and drain ventilators assist in the ventilation of the sewers, but it is only where these are constructed on the most approved principles that such a plan can even be thought of; it would be a danger. ous proceeding in the case of old and badly constructed sewers (see p. 87).
Drains are very often needlessly large, and thus the flush is very much reduced. For example, given two drains of equal fall, carrying the
volume of sewage, the one 4 inches in diameter and the other 6, the rate of travel, and, therefore, the flushing power, in
Fig 26. the former case will be greater than in the latter, because the depth of fluid in the smaller pipe is greater than in the larger. The accompanying sketch (Fig. 26) shows the comparative difference in depth of the same volume of fluid in a 4., 6-, and 9-inch pipe. As a rule, the diameter of house drains need not exceed 4 inches, except in the case of very large establishments. Far to often, even now, a 6-inch pipe is used when a 4-inch would answer all requirements, and, in the case of old houses, one frequently finds that even the tributary drains are constructed of 9-inch pipes.
Whether drains are intended to convey the ordinary waste
water only, or in addition the excreta and urine of a household, they must be constructed with equal care and attention to
Sucketed glazed stoneware or iron pipes are alone admissible. They should be laid as far as possible, in straight lines, with the socket end directed towards the sewage flow, as represented in Fig. 27 (A), not as shown in (B); the fall ought to be uniform, and not less than 1 foot in from 40 to 60. If such a fall cannot be obtained, then some artificial means of flushing, which in all cases is desirable, becomes essential, in order to ensure perfect cleansing of the channel.
Before proceeding to lay the pipes, each one should be caro fully examined, and any that are imperfect should be rejected. In outline they should be perfectly round, otherwise the spigot will not fit accurately into the socket; the internal surface must be smooth and thoroughly well covered with glaze ; and they must be entirely free from cracks or flaws of any description, otherwise the drain will not be water-tight.
The trench in which the pipes are laid should be dug, not piece by piece, but in lengths, and it is important not to interfere with the solidity of the floor by excavating, in the first instance, to a greater depth than is necessary, as this necessitates the replacement of soil and thus causes a risk of after subsidence. If it should happen, in the process of digging, that more soil has been removed than is necessary, in replacing it, so as to equalise the gradient, the replaced soil must be firmly beaten down, otherwise subsidence will afterwards occur which will interfere with the proper flow of sewage, and, possibly, impair the integrity of the joints and cause leakage.
Unless the ground is naturally solid, all stoneware drains should be laid on a bed of concrete 4 inches in depth, and, if it should be found necessary to carry such a drain under a house, it should be entirely imbedded in concrete of at least the same thickness. The latter precaution ought to be observed in all cases where it is necessary that a drain should be laid in close proximity to a well, although, if circumstances permit, it is better to select another route for the drain or use iron pipes.
In laying the pipes, a point of the utmost importance to remember is, that they should rest on their bodies on the bottom of the trench, and not on their sockets, a portion of soil being removed at points corresponding with each socket to allow of this. It is the usual practice of inexperienced drain layers to disregard this precaution, with the result that, when the trench is covered in, in place of the weight of the soil being uniformly distributed along the entire length of the pipe, the pressure is concentrated upon each joint, and, in all probability, causes the recently introduced cement to be expelled from the sockets.
Joints must be made with extreme care, the best Portland cement being alone admissible for stoneware drains. Even now it is not an uncommon practice to use clay for the purpose. An ignorant workman may, possibly, be excused for following past custom in this respect, but builders and architects are greatly to blame if they countenance such a proceeding.
Having carefully cemented the joint, not only at the top, but