TANKS AND GAS-HOLDERS.

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employed; and any one or more of the gas-holders can be filling or emptying, or may beshut off as required, with the same facility as when two pipes are employed, in the usual way,with four times the number of valves. The connecting pipes of four gas-holders only areshown, but it is evident that any greater number could be connected in the same way.

ERICK TANKS.

Plate XXV. represents sections of brick tanks of various dimensions, from ten feet tothirty-eight feet deep.

Fig. 1 represents a section of the wall of a brick tank 10 feet deep, built in ordinarymortar, and puddled over the bottom and round the sides. Walls of the thickness shownin the diagram may be used for tanks of 20 feet diameter. The top course of bricks shouldbe set on edge and laid in cement. Those parts whereon the suspension or guide-columnsrest should be of additional thickness, so as to form piers, into which the foundation-boltsof the guide-columns can be built.

The following is the specification of a tank 31 feet 0 inches diameter, and 12 feet deep :—

Excavation .—The ground to be dug out to the depth of 14 feet 6 inches, of such diameter as maybe requisite, with such slope to the sides as will prevent them from slipping in. Should any partshow a tendency to slip, it must be immediately shored, and the shores must be maintained so asnot to interfere with the building of the walls. The excavation must be kept clear of water till thegas-holder is fixed and’ the scaffolding removed. Well-tempered clay puddle of approved quality tobe used for the covering of the bottom of the tank and for coating the outside of the side walls, inthe following thicknesses :—Over the bottom of the tank, 2 feet 6 inches; on the side walls, 2 feet6 inches, reduced to 1 foot 6 inches at the top. The whole to be well trodden in and backed upwith earth as finished.

Brickwork .—The bricks to be hard, well-burnt stocks. The whole of the mortar must be of thebest hydraulic lime and sharp river-sand well mixed and thoroughly worked together, and in theproportions of a third lime to two-thirds sand. Two double courses of footings with set-offs of halfa brick for each double course; the remaining portion of the wall to be divided into two parts, one8 feet 6 inches high and two bricks thick, and the other 3 feet 6 inches; the walls to be one and ahalf thick, the last or top six courses to be laid iu the best Roman cement. The whole work to begrouted with its respective mortar or cement every four courses. The tank to form a perfectly truecircle, neither more nor less than 31 feet 6 inches in diameter in any direction ; seven piers to bebuilt inside equidistant round the circumference, to receive seven stones hereafter described. Onepier to be built outside on the main point of suspension with dry well of nine-inch work, 2 feetG inches in diameter and 3 feet G inches deep, for counterbalance weights. Two of the piers to bebuilt at the secondary points of suspension. In these piers holding-down bolts and plates to bebuilt in and run in with Roman cement; three other piers are also to be formed by carrying up the2-brick work in the wall solid to the top for 2 feet 6 inches in width.

Masonry .—Seven squared and tooled stones to be set in cement, 2 feet by 1 foot 6 inches byG inches thick, for inside piers, in which there must be formed holes for six lock-nuts. Also threestones, 24 inches by 27 inches by 4 inches thick, for the holdfasts of the girder-rods. One squared