17 December, 1889." SIR JOHN COODE, K.C.M.G., President, in the Chair. The discussion upon the Paper by Professor Osborne Reynolds, "On the Triple-Expansion Engines and Engine-Trials at the Whitworth Engineering Laboratory, Owens College, Manchester," occupied the evening. SECT. II. OTHER SELECTED PAPERS. (Paper No. 2342.) "The Water-Supply of some Italian Towns." By ALEXANDER FAIRLIE BRUCE, Assoc. M. Inst. C.E. As the Author has enjoyed somewhat exceptional opportunities of obtaining trustworthy information on the subject of Italian watersupply, it has occurred to him that a sketch of the water-works of some of the principal towns of Italy may be of interest, especially in view of the anxiety now felt by the Government for the improvement of the sanitary condition of that country. VENICE. This city was for long entirely dependent for water-supply on the rain which fell within its own area, collected in cisterns (Figs. 1 and 2) in the piazzas and courts. This being very insufficient, the Government of the Republic in the sixteenth century made the Seriola Veneta Canal from the Brenta at Dola to Moranzani, the nearest point of terra firma to Venice, whither the water was conveyed in boats and pumped from them into cisterns. The inadequacy of this supply being more and more severely felt, a concession was, in 1875, granted to Messrs. Ritterbrandt and Dalgairns for the construction of an aqueduct and the sinking of an artesian well 1,148 feet deep. They transferred this concession to the Cie. Générale des Eaux in 1879, who, after making some alterations in the original designs, commenced work in 1881, and completed the undertaking in 1883. At a point near the village of S. Ambrogio and 60 feet above datum, a water-bearing stratum, 10 feet thick, consisting of sharp sand overlaid by blue clay, was found only 39 feet below the surface. Into this twenty artesian wells were sunk to a depth of 46 feet. The wells consist of 12-inch pipes, enclosing an inner pipe, with a copper rose at its lower end to exclude the sand. Over the top of each pipe a small vaulted chamber is built below the surface of the ground, into which the water rises freely. Each of these chambers is connected with the principal collector, which is 658 feet long. It is provided with overflow shafts at each end, and divided by a partition up the centre to allow onehalf to be used while the other is being cleaned. At one end of the collector there is a sluice-chamber with a sand-trap 20 inches deep, from which the supply pipe starts. The masonry is all brickwork in hydraulic mortar. The supply pipe is 25 inches in diameter and 16 miles long to Moranzani, laid entirely along the public road at about 6 feet 6 inches below the surface. It is made of Grenoble cement, sand, and fine gravel, 4 inches thick, surrounded with concrete composed of lime, pozzolana, and broken stones, and is capable of delivering 3,000,000 gallons a day, or 22 gallons a head, nearly three times. the quantity considered sufficient in Venice. It is provided with shafts 1 mile apart for overflow and scouring purposes; they also afford means of access to the aqueduct, and enable each section to be isolated for repairs if necessary. In order to admit of the water of the Seriola being used if required, four filtering-beds have been constructed at Moranzani, having an area of 1,360 square yards. The filtering materials consist of a layer of 2 feet 8 inches of sand, 2 feet of gravel, and 1 foot 4 inches of broken stones, 6 feet in all, the floor being of concrete; the rate of filtration is 18 cubic feet per square foot per twentyfour hours, with a head of 3 feet. To enable the pipes to deliver 2,500,000 gallons at tidal water-level 10 feet above datum, or 4,500,000 at 6 feet above datum, in the service reservoir at Venice, the water is raised from 12 feet, the level at which it stands at Moranzani, to 16 feet by a rotary pump driven by a Girard turbine, which is actuated partly by water of the Naviglio Mira-Moranzani, and partly by the overflow from the Seriola Canal. The water is pumped into a caisson, with a capacity of 7,700 gallons, from which the pipe to Venice starts. In case any accident should happen to the pump, provision is made for introducing the water directly into the pipes from the filters. The pipe to Venice is of cast-iron, and is laid below the lagoons; it is 31 inches in diameter, and has a total length of 4 miles. The depth, except where canals are crossed, seldom exceeds 4 feet. The pipes were laid within cofferdams (Figs. 3 and 4); they have a cover of 20 inches, and are supported on piles. At the crossings of the Donena and Scomenzera canals, where the depth of water and current are too great to admit of the pipes being laid in this way, divers were employed. The pipes were jointed throughout with rings of vulcanized india-rubber 3 inches deep, not a very durable description of joint. It appears to the Author that this work might have been quite as efficiently, and considerably more economically, done by using lead joints with a ball-and-socket arrangement between every two ordinary joints, which could have been made on a barge and launched out by degrees. They could have been sunk to the required depth in the mud by dredging; supporting piles appear to have been scarcely required. |