siphon is inside, the ventilating pipe of the siphon may be carried through the wall. Note the arrangements to prevent siphonage in the diagrams of W.C.'s in the preceding figures. 2. Gully-traps. The Anti-D trap" (fig. 70), Fig. 70.-HILLYER'S ANTI-"D" TRAP. These are useful for washings of the yard, waste water, and rain water, but should never be placed inside the house. The diagram shows a yard gully with a grating above and a moveable pan at the bottom to be lifted out with the Fig. 71.-GULLY TRAP WITH MOVABLE BUCKET FOR SEDIMENT. rubbish which has fallen into it. The house pipe should not open immediately over the gully, but into an open channel 18 inches from it. (Model bye-laws of L. G. Board.) Good traps. 1. They should have a water-seal of at least 1 inches in depth to form a certain barrier to gases. 2. They should have no projections or angles for the deposit of filth. 3. They should be situated so that they can be easily flushed with sufficient force to clear them without causing siphonage. 4. They should be self-cleansing. "D" trap fail here.) 5. They should be ventilated. Faults in traps. (Mason's trap, and 1. Liability to unsealing through evaporation of the water, if seldom used. 2. Liability to unsealing through siphonage unless guarded against. 3. Pressure of gas may force water out. (Ventilation of drain prevents this.) 4. The water may absorb sewer-gases at one opening until it is saturated and these gases will be given off at the other surface unless frequently used. 5. They always obstruct the flush of water to some extent. 6. Some are filthy and should be discarded altogether if not self cleansing. The student should make a careful study of the model arrangement of house-pipes for bath, W.C., and sink, sketched in fig. 72. Note particularly the following details: : 1. The W.C. cistern is entirely separate from the supply cistern. 2. The soil-pipe is ventilated. 3. The siphon-traps have an air-pipe to prevent siphonage. 4. The waste-pipes from bath and sink over a gully-trap. PRACTICAL WORK ON CHAPTER VIII. 1. Examine the different forms of W.C. which are available, to verify the text-book descriptions. 2. By means of glass tubing, make a model of a siphon trap. If water coloured with magenta be poured in, it will be seen that the bend retains water (which acts as a barrier to sewer-gas in a real trap). 3. Make a simple siphon by bending a glass tube of about a foot in length, so that one leg is 4 inches and the other 8 inches. When this is filled with water, and the short end placed in a vessel of this liquid with the longer end hanging over the side, the pressure of the air will force water over the bend and the water will flow until air enters the siphon. This will illustrate siphonage. CHAPTER IX. REMOVAL AND TREATMENT OF REFUSE. Sewage may be defined as water containing certain refuse substances in solution and in suspension. It is composed of: 1. The urine and faeces of human beings and animals. 2. Slop-water, including water used in cooking, washing, cleaning, etc. 3. Rainfall. 4. The waste water of factories. For a mixed population the daily average of excreta per head may be taken to be 2 oz. of faeces and 40 ozs. of urine. The manurial value of the urine is about ten times greater than that of the faeces. When diluted with the water from water-closets the addition of these matters to the sewage of a town has very little effect upon the composition or the manurial value of the sewage. According to the first report of the Rivers Pollution Commission the value for agricultural purposes of 12 tons of sewage from towns without water closets is equal to 10 tons of sewage from towns with water closets. The average compositions are thus compared :— Midden towns 82.4 4.2 1.9 5.4 6.4 11.5 17.8 21 8 31.9 Water closet towns 72.2 4.7 2.2 6.7 7.7 10.6 24.2 20.5 44.7 Ammonia. Total Nitrogen. Chlorine. Mineral. Organic. Total. The above numbers represent parts per 100,000. As a matter of fact it is quite impossible to prevent access of urine to sewage. This being the case it makes but little difference whether the solid matter is included or not. Both faeces and urine decompose but slowly if not mixed with water, but when it has been added to them decomposition sets in within 24 hours, resulting in the evolution of foetid organic gases. If these are evolved near the dwelling house they may injuriously affect health. It is important therefore to prevent the mixing of the excreta with water as long as they are retained near the dwelling, and, on the other hand, if they are allowed to mix with water, means must be provided for their immediate and thorough removal. The treatment of sewage is usually considered under two heads the conservancy systems and the water carriage systems. CONSERVANCY SYSTEMS. The old-fashioned 1. The Privy or Midden System. plan, still often met with in country places, was to dig a hole in the ground at the back of the closet. This received the excreta for an indefinitely long period. If the soil happened to be porous the liquid part quickly percolated downwards and polluted the ground water, while the decomposition and liquefaction of the more solid constituents kept pace with their production, so that such middens never required emptying at all. Where the soil was more impervious the pit gradually filled up and was emptied at long intervals. The more modern midden consists of a comparatively water-tight shallow pit which receives the excreta and into which are thrown the ashes from the house. It should be at least 6 feet away from any dwelling and 50 feet away from any spring, well, or stream. Rain must be excluded by a suitable roof, and proper ventilation must be provided. To enable ashes to be readily mixed with the excreta the seat should be hinged. The capacity should be small so that a removal of the contents is fre quently necessary. The floor of the privy must be 6 inches |