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Dr. Angus Smith's composition. The protection of the interior of the pipe is particularly necessary if iron is used in the filtering medium, as otherwise the water becomes distinctly chalybeate if the consumption is slow.

The mode of connecting the pipes together is by slipping the spigot end of one pipe into the socket of the next, and then making the joint. Diagram No. 3 shows the ordinary method of joining pipes. No. I is the ordinary" yarn and lead” joint, and No. 2 the "turned and bored "joint. In No. I the best white yarn is caulked in to a depth of about 24 inches, and the rest of the space run in with soft lead,

Diagram 103

which is afterwards well set up or caulked one-eighth of an inch within the rim of the socket. The chief point to be observed is that no part of the yarn should find its way into the interior of the pipe. In No. 2, the turned spigot is simply brushed with cement or paint, and pushed home into the bored socket. The extra space is sometimes run with lead and sometimes left. The most approved modern system is to run the joint solid with lead without the yarn, a strip of drawn lead being inserted in the bottom of the socket in lieu of yarn.

For connecting the service mains suitable cast-iron branches are introduced. The cocks used for regulating the flow of the water consist of a door, which is raised or lowered by means of a screw worked from the surface, as shown in Diagram No. 4. For the purpose of supplying water in case of fire or other emergency, openings are left in the mains, which are closed in some old waterworks by wooden plugs, but in all recently constructed ones by hydrants, which are undoubtedly to be preferred. The description of these, however, properly belongs to the section treating of the supply of water for extinguishing fires, and a full account of the various forms in use will be found in the special paper on “Water Supply for Fire Extinction,” by Mr. J. H. Greathead, C.E.

Diagram 14.

a

Each house is connected with the service pipe or main, by a pipe called the “house-service pipe,” the connection being made by means of a ferrule screwed into the main. The house-service pipe is generally of lead, but as some waters have a chemical action upon this metal, drawn-iron

, pipes, either glazed, galvanised, or otherwise protected, are substituted. Where the system of “constant supply" prevails, an apparatus is used in order to avoid inconveniencing the consumer, which enables the ferrules to be inserted while the main is still charged and under pressure.

The depth at which mains should be laid varies according to circumstances, but may be taken in temperate climates to be from two to three feet from the surface of the ground to the top of the pipe. In colder climates the mains should be laid at sufficient depth to escape the action of frost,

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which, generally speaking, does not extend below four to five feet. When mains are laid at this depth, the cost of laying as well as making house connections and effecting repairs is considerably increased. When the temperature of the water varies considerably at different seasons, the length of main is affected. Where "socket joints” are used, little damage is done, but with “ turned and bored joints” it will generally be found in autumn that some tightening up of the joints is necessary, unless special provision is made for the contraction that then takes place.

Where pipes are carried across openings they should be protected from the changes of temperature, which can conveniently be done as shown in Diagram No. 5, in which the pipe is shown enclosed in a wooden casing, the circular

Diagram 105

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space being filled in with felt, sawdust, or other nonconducting material. In laying mains across bridges, great care should be taken for their protection. It will often be found that there is not sufficient depth from the surface to the arch or girder of the bridge to allow of the pipes being laid ; when this is the case, it is convenient to carry the mains on cantilevers at the side of the bridge, the pipes being enclosed in a casing of wood or other material, as shown in Diagram No. 5. In new bridges it is generally arranged to leave sufficient space for a subway below the footpaths ; this, as a rule, is a very convenient way, as it allows of repairs being effected without interfering with the ordinary traffic.

The system of distribution hereinbefore described refers

mostly to the distributing pipes within the town. In some exceptional cases, owing to local circumstances, wooden pipes, similar to those which were used before the introduction of iron pipes, are still used, and in places where freight and carriage are difficult, pipes formed of sheet iron or steel can, owing to their lightness, be more economically used than those of cast iron. Pipes have been made of paper prepared with bitumen and several other substances, but have not been proved able to withstand the severe tests to which water pipes are subject. Where the pressure is very great, as for instance where water is distributed for hydraulic power, the pipes are cast of extra thickness, and a “faced ” flange joint with an india-rubber ring inside a recess, into which a projection on the next pipe fits, is sometimes substituted for the socket joint.

The construction of the aqueduct conveying the water from the source to the distributary mains varies with circumstances. If the water is conveyed under pressure, one of iron is necessary, and preferably of cast-iron, which, being laid under the surface of the ground, is better in all respects (apart from cost) than any other. The pipes are so placed as to follow pretty closely the undulations of the ground, an emptying valve being fixed at the bottom of every fall, and an air escape valve at every summit. When large quantities of water, however, have to be conveyed, aqueducts of masonry, brickwork, or concrete, have to be adopted. These, unlike pipes which can be made to follow the inequalities of the ground, have to be laid to a regular gradient. Provision is made for draining such aqueducts, and overflows are placed along their length to prevent damage in case of the flow of water being interrupted. All aqueducts of masonry, &c., should be covered, but this is not always possible when they are of large size. Size, indeed, renders the covering less necessary, provided precautions are taken to prevent the infiltration of land drainage, as the large quantity of water flowing down is less liable to be affected by the sun, while the conduit, being uncovered, can be easily and completely cleansed at all times.

The cross section varies with the materials employed ; those of brickwork and concrete being generally of an oval or circular form, whilst those of masonry are usually constructed with a rectangular section, and when covered, are sometimes arched over, and sometimes covered with slabs. For the aqueducts, tunnels often have to be made through hills, and conduits over valleys. These latter, when there is sufficient head of water available, are usually crossed by syphons of cast-iron pipes. When, however, the head of water cannot be spared, the aqueduct is carried across the valley at the regular gradient, and supported by piers of masonry, or other suitable material. In this case, the aqueduct is sometimes continued in masonry, brickwork, or concrete, or a trough or tube of wrought iron is substituted. This trough is sometimes made of pipes of sheet iron or steel, riveted together throughout the full length of the crossing, and suspended and braced by wire cables or rods, similarly to a suspension bridge.

One of the most important of modern aqueducts is that bringing the water of the River Vanne to Paris, the length of which is about 90 miles, with 23 syphons of wrought-iron pipes.

The chief points to be observed in the designing of a complete distribution should be-(a) that the water, which before entering the mains is in its purest state, should be delivered to the consumer in a similar state, and suffer no contamination on the way ; (6) that the mains should be of sufficient area to allow an ample quantity of water to pass to meet all contingencies; and (c) that a constant circulation should be maintained of about 3 ft. per second so as to prevent any deposit taking place.

DUAL SUPPLY.

In the case of many large towns, an abundant supply of water of inferior quality is found in close proximity, while further off, but still within reasonable distarce, a limited supply of better water exists. In considering such cases, it often becomes a question as to the advisability of adopt

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