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an hour and three quarters on an average, and requires the consumption of about oneand a half or two cwt. of coke; in some places the boiler and tender are suppliedwith hot water by means of a stationary boiler, in order to expedite the getting up ofthe steam, and also as a means of economy.
The area of the fire-grate is 9-| square feet; it is 18 inches below the bottom ofthe lowest tubes, and the space for the fire when quite filled up to the tubes is 14cubic feet, and holds about 2-| cwt. of coke; but the fire-box is not always filled sofull as this, and usually contains about one and a half or two cwt.
The surface of water exposed to the heat directly radiated from the fire is thewhole surface of the internal fire-box, deducting the fire-door and the tubes, and isequal to 50 square feet; and that exposed to the current of hot air, or conducted heat,is the interior surface of the tubes, and is equal to 432 square feet. The surfaceexposed to radiated heat is considerably more efficacious in generating steam thanthat exposed to conducted heat only, as the supply of heat is more copious, and theproportion was found to be about three times in an experiment tried by Mr. Stephen-son, which is the only one that has been made upon the subject; the experiment wasmade with an old engine and the proportion may be somewhat different in the mo-dern engines.
The area of passage for the heated air from the fire-box to the chimney is thesectional area of all the tubes inside the ferrules ; the ferrules are three eighths of aninch less than the outside of the tubes, and are therefore an inch and a quarter in diame-ter inside; and the sectional area of them all, (124 in number,) is T06 square feet.The area of the passage through the chimney is rather more, or P23 feet.
In the Rocket engine the area of passage through the tubes was '90 square feet ornearly the same as in this engine, though the fire-grate was but half the size ; butthe heating surface of the tubes was only one third, from the large size and smallnumber of the tubes ; the heating surface of the fire-box was also only three quartersof that of the present engine.
In the old engines before the Rocket , the area of passage through the flue wastwo and a half times the size, but the heating surface was only one thirteenth ofthat in the present engine; the fire-box had also only one fifth of the heating surface;the fire-grate was three quarters of the size.
THE CYLINDERS AND THE MANNER OF USING THE STEAM.
Steam Pipe.—S S, (Plates XC. and XCII.,) is the steam pipe for conveying thesteam from the boiler to the cylinder where it is to be used; it is made of copperthree sixteenths of an inch thick, and the part within the boiler is 5 inches’ diameter in-side ; it passes through the tube plate of the smoke-box and is bolted to it by a flanch.The pipe then divides into two smaller ones, 3| inches in diameter, which pass down