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the length of the boiler, added to the width, and multiplied by 175 to obtain that of effective surface; hence,

147-5×1-75

24-26×2+606

=47 feet, depth of side fue.

3. To determine the dimensions for a cylindrical boiler.

Rule.-Extract the square root of 1·34 times the effective heating surface in square feet, and twice the root equal the boiler's circumference in feet; also, the circumference equal the length.

Ex. Let a cylindrical boiler be required with an effective heating surface of 86 square feet; what must be its length and diameter in feet?

86×1·34=10-74×2=21·48 feet circumference, or 6 feet 10 inches diameter, and 21:48 feet in length.

Note.-When an internal flue is to be inserted in a boiler, the external surface of the boiler may be diminished in length equal to half the exposed surface of the flue. Observe, also, that the height of the contained water in boilers generally ought to be about 3rds the whole height of the boiler.

Marine Engine Boilers have become so varied in their designs, that any attempt at enumerating-by ever so slight a description—those that may be considered worthy of record, would much exceed the limits of my present purpose; but having been favoured by Messrs. Bury, Curtis, and Kennedy, with particulars of the boilers constructed by them for the 'Braganza' steam vessel, and which have given the highest degree of satisfaction in every respect, I annex designs and data, in preference to those of any other description. (See Plate K.)

These boilers are constructed so as to work at 10 lbs. per square inch if required; they are four in number; the diameter of each cylinder is 621 inches, length of stroke 54 feet, or calculated velocity bout 231 feet per minute: the nominal power of each

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Plate K

Plans of the Boilers on board the Peninsular Cos Steam Ship Braganza By Mess's Bury, Curtis and Kennedy, Liverpool

Ground Plan

W. T., del.

6. Gladwin, se.

London J. Weale, 1853

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Plans of a Locomotive Engine Boiler
of the most approved Construction

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Plate i

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engine is 140 horses, and the heating surface per horse-power is 14.1 square feet.

Now 14.1X140-1974 square feet to each engine.

Then as per rule (page 268), 375 multiplied by the area of cylinder or 21 feet, and by the velocity per minute or 231 feet, and divided by 1044 (see Table, page 258) or volume of steam to 1 of water, at 10fbs. per square inch, equal 1742-4 square feet; to which add about th of the quotient, or 217.8, for side or vertical surface, equal 1960.2 square feet to each engine, thus nearly corresponding with their given quantity of heating surface.

Note. In the four boilers there are 608 brass tubes, 6 feet in length and 3 inches in diameter. The length of each fireplace is 5 feet 10 inches, and breadth 2 feet 10; there are, 56 of a square foot of fire-bar to each cubic foot of cylinder capacity, and 16 of a square foot of tube aperture to each square foot of fire-bar, the openings of the tubes being reduced by the thickness of the tube hoops. The diameter of each chimney, of which there are two, is 3 feet 5 inches.

Locomotive Boilers, in the manner of their construction, are a class which, of necessity, demand the utmost degree of qualified attention, because of the great pressures they are required to sustain, and the unavoidably narrow limits in which such vast volumes of steam are required to be generated.

In boilers of this description, it is of the most essential consequence that the water spaces in the fire-box be of a sufficient width, say, on the back and sides, not less than 2 to 3 inches, and in the front, where the tendency of the fire is urged by the action. of the blast-pipe, at least 3 inches.

The boiler which I have selected for illustration (see Plate L) is of the most modern description; and from an intimate knowledge of its performances, I am enabled to assert, with full confidence, that it possesses efficient and economical properties to the production of steam.

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About 112 lbs. of coke consumed in this boiler evaporate 84 gallons of water; and from 20 to 25 lbs. of coke are consumed per mile.

Heating Powers of Combustible Substances.

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In regard to the giving of an order for a steam engine of any required number of horses' power, it has been argued and ultimately decided, that in a commercial point of view the order is not sufficiently completed by the dimensions of cylinder, boiler, &c. being of ample magnitude to produce the specified dynamical effect in horses' power; and not unless corresponding with the established custom by Boulton and Watt, or that of other manufacturers of equally well known respectability: hence, generally, the fol

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