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pools, and they still go by this name in some parts of the country. They may be much improved by making the end nearest to the house vertical, giving the opposite one a gentle slope, and fixing the dipstone, not vertically, but slanting in the direction in which water goesrounding off the inside with concrete rendered in cement, so that there are no angles or corners. Thus the water falls vertically into the trap and flows out through a gentle incline. In such a trap very little accumulation occurs. Stoneware siphon traps are, however, now almost entirely used. They are frequently made with an upright piece from the lower part of the siphon, which may be continued by means of straight pipes up to near the surface of the ground, for the purposes of inspection, and of cleaning out the siphon should it get blocked up. This inspection opening is now sometimes made at the end of the siphon which is intended to be placed next to the house, so that if pipes are carried from it up to the surface of the ground, and an iron grating put on to it, a passage is formed which, under ordinary circumstances, acts (if precautions are taken which will be presently mentioned) as an entrance for air into the house sewer. The siphons also are now made with the limb into which the house sewer opens nearly vertical, while the opposite limb has a gentle slope
already mentioned. It is a considerable improvement, although not absolutely necessary, to increase the air inlet into the sewer at this point, that is to say, immediately on the side of the siphon trap, and instead of merely having a pipe taken up to the surface of the ground, to have a man-hole built in brickwork, and with channel pipes instead of whole pipes running along the bottom of it into the siphon. The channel pipes and one or two pipes beyond should be laid at a considerable fall, so that the water may rush down into the siphon and clear it out as much as possible. main in the man-hole by means of channel pipes, or even by whole pipes discharging into a gutter built above the channel pipe; or they may of course be taken into the house sewer at any point of its course. The man-hole may be covered by a galvanized iron-locked grating, if it is in such a position that gravel, &c., is not likely to get into it, but if in an area it is better to cover it with a locking iron door, and to have one or two 6-inch ventilating pipes from its upper part carried under the pavement area to the wall, up in the wall a short distance, and then opening out by gratings flush with the surface of the wall. A junction pipe should be fixed immediately beyond the siphon and pipes brought from it through the wall of the man-hole, the end being filled with a plug, which can be removed for the purpose of cleaning the sewers beyond the siphon if necessary, or various earthenware disconnecting traps may be used. Potts's Edinburgh chambered sewer trap has the advantage of having a large air inlet, and a considerable fall in the trap itself. In many instances, with sewers already laid, sufficient fall cannot be got to introduce these traps. Weaver's trap is really a siphon, as already mentioned, with an upright air inlet leading into the limb of the siphon nearest to the house. Beyond the siphon an aperture is provided by means of which the main sewer, or cesspool beyond, can be ventilated, or which, if merely plugged, may serve as an inspection pipe, through which rods can be pushed, if necessary, down into the main sewers or cesspool. In Buchan's and Latham's traps the fall is quite vertical.
Stiff's interceptor may be described as a siphon-shaped trap, with a double dip, so that it has three compartments, with an open grating for the middle one. If any sewer air should pass under the first dip, it cannot get under the second, which is deeper, but will escape into the open air through the grating. Two inspection openings are provided, which
may be also used as ventilating openings—the further one to ventilate the main sewer or cesspool, if necessary at this point, by means of a pipe running to the top of the house, and the one on the house side of the trap may be used as an air inlet. Professor Fleeming Jenkin has introduced the plan of using two siphon traps with an open grating between them. Dr. Woodhead has modified this by having a large earthenware receptacle, which all the house pipes enter underneath a large iron grating, with two siphons beyond the receptacle, one after another, and an upright pipe with an open grating between them. There is also a smaller upright pipe, with open grating at the top between the receptacle and the commencement of the first siphon. It is unfortunate that we cannot do without a water trap at all in disconnecting the house sewers from the mains, and I certainly do not think that any sufficient reason has been made out for having two traps one after another. At the highest point of the