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 No4.

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,

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 No 5

C

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; (b) 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 distance, a limited supply of better water exists. In considering such cases, it often becomes a question as to the advisability of adopt

In

ing both sources of supply, the latter for drinking purposes, and the former for domestic and manufacturing uses. the opinion of the writer, a system of dual supply is not practicable for domestic purposes, but only for municipal or manufacturing requirements. In cases where water is used for power, a dual supply may also be considered indispensable, as the great pressure necessary for its economical use for this purpose is undesirable for a domestic supply. Again, a separate supply for municipal purposes can be used for road watering, sewer flushing, fires, &c., without affecting the domestic supply. In most manufacturing towns the factories are grouped together, and require large quantities of water at a very cheap rate, which, supposing the water is not used in any way for alimentary purposes, can often be supplied from sources sufficiently pure for purposes of manufacture, although the water may be unfitted for household consumption. Such a supply exists at Roubaix, in France, where the cheapness of the water contributes to the prosperity of the town.

Paris also is supplied in the same manner, there being a double set of mains in the streets, one for domestic purposes, and the other for street watering, &c. The supply of potable water, however, is limited, and in time of drought has to be supplemented by water drawn from the Seine.

A dual supply for domestic purposes would entail a considerable extra outlay on the construction of works, as a double line of mains would be necessary in every street, and the cost of most of the house fittings would be doubled, as they would have to be in duplicate. Another objection is the probability that the excellent quality of the water supplied for potable purposes would cause the quality of the other to be little considered, and the latter might deteriorate, or become subject to great contamination. Consumers, bearing this in mind, would probably use the purer water almost entirely. In ordinary times, this might not be of much consequence, but in times of drought it might be serious. This difficulty, it is reported, has just