AQUEDUCT
509
must be jointed before being lowered into the previously di edged ground, the detached portions of the built aqueduct must trench. This was the case at the Willamette river, Portland, be connected by rows of pipes laid beneath, and follow- Oregon, where a length of 2000 feet was required. 1 he pipes are ing the main undulations of, the surface. . In of cast iron 28 inches in diameter, inches thick, and 1/ feet long. Aqueduct guc|1 cases t]ie aqueduct terminates in a The spigots were turned to a spherical surface of 20 inches radius ,a l n the inside of the sockets being of a radius § inch greater. . f° chamber of sufficient size to enclose the mouths outside, pp s the insertion of the spigot into the socket, a ring, 3 inches several pipes, which, thus charged, carry After Gf deep, turned inside to correspond with the socket, was bolted to the water under the valley up to a corresponding the latter, the annular space then being run with lead. These chamber on the further hillside from which the built pipes were laid on an inclined cradle, one end of which rested on the bed of the river and the other on a barge where the jointing aqueduct again carries on the supply. These connecting was done : as the pipes were jointed the barge was carefully pipes are sometimes called siphons, although they have advanced, thus trailing the pipes into the trench {Trans. Am. nothing whatever to do with the principle of a siphon, Soc. G. E. vol. xxxiii. p. 257). As may be conjectured from the the water simply flooring into the pipe at one end and out pressure which they have to stand, very great care has to be taken the manufacture and handling of cast - iron pipes of large at the other under the influence of gravity, and the in diameter, a care which must be unfailing from the time of casting pressure of the atmosphere being no element in the case. until they are jointed in their final position in the ground. They The pipes are almost always made of cast-iron, except in are cast vertically, socket downwards, so that the densest metal such cases as the lower part of some siphons, where the may be at the weakest part, and it is advisable to allow an extra of metal of about 12 inches, which is subsequently cut off m pressure is very great, or where they are for use abroad, ahead lathe. An inspector representing the purchaser watches every when considerations of weight are of importance, and when detail of the manufacture, and if, after being measured in every they are made of rolled steel with riveted or welded seams. part and weighed, they are found satisfactory they are proved It is frequently necessary to lay them in deep cuttings, in with internal fluid pressure, oil being preferable to water for this which case cast-iron is much better adapted for sustaining purpose. While under pressure, they are rapped fiom end to end with a hand hammer of about 5 R> in weight, in order to discover a heavy weight of earth than the thinner steel, though defects. The wrought-iron rings are then, if required, shrunk on the latter is more adapted to resist internal pressure. Mr to the sockets, and the pipes, after being made hot in a stove, are D. Clarke in the Trans. Am. Soc. C. E. vol. xxxviii. p. dipped vertically in a composition of pitch and oil, in order to 93, gives some particulars of a riveted steel pipe 24 miles preserve them from corrosion. All these operations are performed cover. A record should be kept of the history of the pipe long, 33 to 42 inches’ diameter, varying in thickness from under from the time it is cast to the time it is laid and jointed in the 0-22 inch to 0375 inch. After a length of 9 miles had ground, giving the date, number, diameter, length, thickness, and been laid, and the trench refilled, it was found that the proof pressure, with the name of the pipe-jointer whose work crown of the pipe had been flattened by an amount vary- closes the record. Such a history sometimes enables the cause is often very obscure) of a burst in a pipe to be ascertained, ing from l inch to 4 inches. Steel pipes suffer more (which the position of every pipe being recorded. _ from corrosion than those made of cast-iron, and as the Cast-iron pipes, even when dipped in the composition referred metal attacked is much thinner the strength is more to, suffer considerably from corrosion caused by the water, seriously reduced. These considerations have prevented especially soft water, flowing through them. One pipe may be found in as good a condition as when made, while the next may any general change from cast-iron to steel. be covered with nodules of rust. The effect of the rust is twofold; reduces the area of the pipe, and also, in consequence of the Mr Clemens Herschell has made some interesting remarks {Proc. it offered by the rough surface, retards the velocity of the Inst. C. E. vol. cxv. p. 162) as to the circumstances in which resistance water. two results, especially the latter, may seriously steel pipes have been found preferable to cast-iron. He says that diminish These the capability of discharge, and they should always be it had been demonstrated by practice that cast-iron cannot compete allowed for in deciding the diameter. Automatic scrapers are with wrought-iron or steel pipes in the States west of the Uocky sometimes used good results, but it is better to be independent Mountains, on the Pacific slope. This is due to the absence of of them as longwith as possible. In one case the discharge of pipes, coal and iron ore in these States, and to the weight of the imported 40 inches in diameter, found to diminish at the rate of about cast-iron pipes compared with steel pipes of equal capacity and 1 per cent, per year; was in another case, where the water was soft strength. The works of the East Jersey Water Company for the and where the pipes were in diameter, the discharge was supply of Newark, N.J., include a riveted steel conduit 48 inches diminished by 7 per cent, 40in inches ten years. An account of the state in diameter and 21 miles long. This conduit is designed to resist of two cast-iron mains supplying Boston with water is given in the only the pressure due to the hydraulic gradient, in contradistinc- Trans. Aon. Soc. C. E. vol. xxxv. 241. These pipes, which tion to that which would be due to the hydrostatic head this were laid in 1877, are 48 inches in p.diameter and 1800 feet long. arrangement saving 40 per cent, in the weight and cost of the they were examined in 1894-95, it was estimated that the pipes.8 For the supply of Rochester, N.Y., there is a riveted When of rust covered nearly one-third of the interior surfaces, steel conduit 36 inches in diameter and 20 miles long; and for tubercles bottom of the pipe being more incrusted than the sides and Alleghany City, Pennsylvania, there is a steel conduit 5 feet m the They had central points of attachment to the iron, at which diameter and nearly 10 miles long. The works for bringing the top. doubt the coating was defective, and from them the tubercles water from La Vigne and Yerneuil to Pans, include a steel mam no spread over the surface of the surrounding coating. In this case 5 feet in diameter between St Cloud and Paris. were removed by hand, and the coating of the pipes was not Cast-iron pipes rarely exceed 48 inches m diameter and even th s they in the process. Cast-iron pipes must not be laid in contact diameter is only practicable where the pressure of the water is injured cinders from a blast furnace with which roads are sometimes low. In the Thirlmere aqueduct the greatest pressure is nearly with made, because these corrode the metal. Mr Russell Aitken {Proe. 180 lb on the square inch, the pipes where thislaroccurs1 6being 40 C. E. vol. cxv. p. 93) found in India that cast-iron pipes inches ij inches imvuco thick. These g? ii P?; -,3’'up „ Inst. inches m in diameter diameter anu and If DU lieu. in Ill the LIIO hUli buried soil rapidly corroded, owing to the jypresence of nitric v are usually made in lengths of 12 feet, are generally cast with a acid secreted «Arreted by bv bacteria which attacked the iron. The large castsocket at one end for receiving the spigot end of next pipe the iron pipes conveying the water from the Tansa reservoir to Bombay annular space being run with lead, which is prevented from flowing are laid above the surface of the ground. Cast-iron pipes of these into the interior of the pipe by a spring ring subsequent y removed large diameters have not been in existence sufficiently long to the surface of the lead is then caulked all round the ojfeide of the enable their life to be predicted. A main, 40 inches in diameter, pipe A wrought-iron ring is sometimes shrunk on the outer rim conveying soft water, has been in existence fifty years at Manchester, of Hie socket, previously turned to receive it, m order to strengthen and is apparently as good as ever. In 1867 Mr J. B. Francis it against the wedging action of the caulking too . no apparent deterioration had taken place in a cast-iron the pipes are cast as plain tubes and joined with double colfa , found that 8 inches’ diameter, which was laid in the year 1828, a period which are run with lead as in the last case The reason for main, thirty-nine years {Trans. Am. Soc. C. E. vol. i. p. 26). These adopting the latter type is that the stresses set up m the thicker of metal of the socket by unequal cooling are thereby avoided a v y two instances are probably not exceptional. usual place for pipes to crack under pressure being at the back Pipes in England are usually laid with not less than the socket. The method of turning and boring a portion slightly 2 feet 6 inches of cover, in order that the water may not tapered, of spigot and socket so as to ensure a watertight junction by close annular metallic contact, is not suitable or arS® P P ’ be frozen in a severe winter. Where they are laid in though very convenient for smaller diameters m even g • deep cutting they should be partly surrounded with conSpherical joints are sometimes used where a line of mam has to be crete, so that they may not be fractured by the weight of laid under a large river or estuary, and where, therefore, the p p
