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fitting around the bottom of the boiler, with two fire- and two ash-pit doors. The fire-doors are arched, and are provided with cast-iron liners bolted to the doors. The furnace part of the front should be arranged for lining with firebrick, and have cast-iron arches over the fire-doors to prevent brick from falling down if loosened, and be also provided with flanges for securely binding into the arch, and a cast-iron angle-plate bolted on to support the grates. The smoke-boxes for boilers less than 44 inches in diameter have usually one door, and the furnace fronts have one fire- and one ash-pit door.

The boiler fixtures usually comprise the smoke-box and furnace front, as described above, grates, grate bearers, rear arch bars, door and frames for rear ash-pit, safety valve, steam gauge, water gauge fitted to stand pipe, gauge cocks (3) with pipes, whistle and pipe, blow-off valve, check valve, stop valve, smoke-stack and guy rods, and all archbinder bolts, with nuts and outside plates necessary for properly securing furnace front and smoke-box in position in the arch and binding arch together.

Grates for boilers having 7-feet and 8-feet tubes, are 36 inches long; with 10-feet tubes, 44 inches; with 12-feet tubes, 48 inches; and with 14, 15, and 16-feet tubes, 54 inches long, and the width of the grates in all cases equals the diameter of the boiler.

Smoke-stacks for these boilers are generally made of iron, up to 28 inches diameter, of No. 16, and larger sizes of No. 14 iron.

CHAPTER XXVIII.

THE TUBULOUS BOILER.

THIS form of steam-raiser has come rapidly to the front of recent years, its construction being now much superior to what it was when it first attracted attention. The use of cast-iron connections between the tubes has been discarded for wrought iron, or steel forged into shape under hydraulic pressure.

Its convenience for transportation is great; it may be made in pieces small enough for carrying on mule-back.

Repairs are easily effected by comparatively unskilled labour, if spare parts are provided, while immunity from accident is the strong feature of the system. Tubes are employed to carry the water under heat, which are capable of resisting many times the working pressure, and thus for all high pressure the tubulous boiler is the safest to be employed.

Some of them are now made in a rather clumsy yet useful portable form, a list of which are appended, and the introduction of their use into marine practice has already begun. A disadvantage under certain conditions is the cumbrous proportion of the brickwork and great height of the apparatus, but the following table of a well-known type of these boilers gives information enabling a comparison to be drawn with other boilers as to space, weight, and other features. The cost of such boilers varies considerably with locality, but they may be averaged at about £30 or $150 per ton weight.

TUBULOUS STEAM-BOILERS.-D. K. Clark.

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The length of fire-grate in English practice is somewhat less than above.

At a close comparative test in 1876 between one of these boilers and a Lancashire, the following were comparative results :

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Indicated horse-power at 30 lbs. of water per horsepower, 70 lbs. pressure

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Coal burned per hour per square foot of grate area.

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Water evaporated per lb. of coal

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By which it will be seen how closely these excellent forms of steam-raisers approach each other in economy, the advantage gained by the tubulous form being due to its superior quantity and disposition of heating and grate surface.

In a portable form the tubulous boiler may be obtained as follows:

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The following proportions of tubulous boilers are those of the "Belleville," a type which finds much favour on the European continent. They are based on the use of a pressure of 170 lbs. per square inch, or, say, 150 to 160 lbs. working pressure at the engine, and are thus very suitable for use with triple-compound engines.

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