Chap. XXI. STEAM CONSIDERED AS A MOVING POWER.
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The velocities of these engines have frequently exceeded 41 miles per hour, and theSafety-valve is so constructed as to liberate the steam in an admirable manner, the principlebeing to diminish the resistance in proportion to the opening of the valve, contrary to thatpractice where springs and levers are used, the improved valve being made capable ofregulation for any intensity of resistance.
A locomotive engine and tender made by Messrs. Hawthorne for the Versailles line hasthe
Diameter of cylinders - 12 inches.
Steam way to cylinder - length 6^, width 1^ inches.
Length of stroke of piston - - - - - 18 inches.
Boiler 8 feet long, 39 inches in diameter, contains 121 tubes 1| inches in diameter, exteriorlength of tubes 8 feet, and presenting a surface exposed to contact with heated air of428*40 square feet
Fire-box ------- length 30, width 41J inches.
Height above the bars ----- 40^ inches.
Area of fire-grate ------ 8*59 square feet.
presenting a surface exposed to radiant caloric of • 46 T 6 square feet.
Quantity of fuel contained in fire-box to the height of the
lowest row of tubes ----- 1360 cube feet.
Diameter of chimney ----- 14 inches.
The wrought-iron driving wheels - - - - 5| feet diameter.
supporting wheels - 3£ feet diameter.
Weight of engine, without water, in boiler - - - 8 tons 12 cwt.
with water, - - - - 10 tons.
Consumption of Fuel .—When coals are used the same quantity is required as of goodcoke, which varies with different engines from half a pound to a pound per mile for everyton of load: the latter is perhaps nearest the truth upon level lines.
In locomotive engines the power does not depend altogether upon the diameter of thecylinders, a certain quantity of steam being produced each moment; if the diameter of thecylinder be increased, the number of strokes will be diminished, or the steam will have lesselasticity ; and if the diameter be less, then a greater elasticity or pressure per square inch isobtained, or an increased number of strokes : the quantity of steam being limited, the powerof the engine depends entirely upon the number of times the cylinders can be filled duringa minute, or the quantity of steam that can be generated or water evaporated in a giventime. The elastic force of the steam is also partly diminished before it reaches the cylin-ders, by being obliged to pass through the small apertures of the pipes: and the pressureupon the piston is less than against the steam-valve in the boiler, which is still further dimi-nished when the engine increases in velocity.
The Killingworth engine had a boiler 9 feet 2 inches in length, and 4 feet in diameter iwithin it was an elliptical tube which contained the fire, 2 feet 4 inches broad, 2 feet high,and 4 feet 8 inches long. The area of the fire-grate was nearly 13 square feet; the numberof tubes 43, the radiant surface 22^ square feet, and that of the communicative surface 101feet 6 inches. The volume of heated air which passed through the tubes was equal to 135square inches ; the load 60 tons, exclusive of the tender, and the velocity upon a level road9 miles per hour. The quantity of water evaporated per hour in this instance was 279gallons, and of coal consumed 14^ pounds for every cube foot of water converted into steam.
By another experiment it was found that the same engine with a load of 40 tons,travelling at the rate of 9 miles per hour, evaporated 40 cube feet of water, or 247 gallonsper hour, with about 13 pounds of fuel for each cube foot evaporated : in one of the earlyexperiments made at Liverpool, the Rocket engine, whose fire-grate contained an area of6 superficial feet, a radiant surface of 20, a communicative surface of 118 square feet, witha load of 40 tons, going a velocity of 13 miles an hour, evaporated during that time only30 cube feet of water, which shows the improvements that have been made since thattime. By Mr. Watt’s experiments, it required 8 feet of surface to be exposed to thedirect action of the fire to evaporate a cube foot of water in an hour, and 10 cubic feet wereconverted into steam with 84 pounds of coal; in many locomotive engines, it requiresupon an average 19 pounds of coal to convert a cube foot of water into steam, which ismore than 2\ times Mr. Watt’s estimate; there is therefore at present in some instances avery great loss in the application of fuel to locomotives: upon the Killingworth railwaythe average of several years’ consumption for the engines employed was 2*12 pounds perton per mile; on the Darlington railway, 2*16 pounds; upon the Bolton and Leighrailway 2*03 pounds per ton per mile.
Railway Hydraulic Traversing Frames , used at the Bristol terminus of the Great Western , formoving the railway carriages from, one line of railway to the other , without the use of theturntable. — This machine is a wrought-iron frame, strongly braced and tied togetherlaterally and diagonally; at each of the four corners is placed a cast-iron hydraulic press,
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