of water required for steam per minute, from whence the proportions of the boiler may be determined.* At the common pressure of two pounds per circular inch on the valve, the divisor will be 1497. The quantity of injection water should be twenty-four times that required for steam, and the diameter of the injection pipe one-thirty-sixth of the diameter of the cylinder. The valves in the air pump bucket should be as large as they can be made, and the discharge and foot valves not less than the same area.

Summary of proportions of a double engine, working at full pressure.-The length of a cylinder should be twice its diameter; for a cylinder having this proportion exposes less surface to condensation than any other enclosing the same quantity of steam. The area of the steam passages should be about one-fifth of the diameter of the cylinder; or their area should be equal to the area of the cylinder, multiplied by the velocity of the piston in feet per minute, and divided by 4800. The diameter of the air pump should be about two-thirds of the diameter of the cylinder, and half the length of stroke; and the larger the passages through the air bucket and the discharging flap are, the better. The quantity of water for injection should be about 23 times that required for steam, or about 26 cubic inches to each cubic foot of the contents of the stroke of the piston. Watt considered a wine pint, or 283 cubic inches, quite sufficient. There should be 62 times as much water in the boiler as is introduced at one feed.

These proportions are taken from Tredgold's valuable treatise on the steam engine.

RAILWAYS, STEAMBOATS, &c.

IT has been deduced from very extensive experiments on the Liverpool and Manchester railways, that the effective power of a locomotive engine is about 3 of the pressure of the steam on the piston, on the calculated power of the engine being 1. In one case, for instance, a cylinder 21 inches diameter was used, the elasticity of steam in the boiler was 30 lbs. to the square inch, above the pressure.

* To 459 add the temperature in degrees, and multiply the sum by 76.5. Divide the product by the force of the steam in inches of mercury, and the result will be the space in feet the steam of a cubic foot of water will occupy.

of the atmosphere. The length of the rail, which was inclined, was 3165 feet, and the height 24 feet. The time of drawing 6 loaded wagons, each weighing 9010 lbs. up the rail, was 570 seconds, during which time the engine made 444 single strokes, each 5 feet long. Now,

21 × 7854 = 346.36 the area of the piston in square

=

inches, wherefore, 346·36 × 30 10390 lbs. the pressure of steam upon the piston, whose stroke was 5 feet, and number of strokes in the given time 444; hence 444 × 52220 feet the space through which the power 10390 has traversed; therefore, 10390 × 2220 23065800 lbs. = the impelling power of the engine. Now, it was found that the actual weight including resistance moved, was 7124415 lbs.; then,

7124415

23065800

which will give the effect about 30.9 per

cent., but the foregoing number may be taken as a safe medium, that is, 30 per cent or 3.

The amount of retardation, arising from steam carriages moving on railways, has been estimated thus;

Loaded carriages weighing altogether 8522 lbs. the friction amounted to 50 lbs., or the part of the weight. In empty carriages weighing 2586 lbs., the friction amounted to 10 lbs., or the part of the weight; and the friction may be regarded as a constant retarding force. Wrought iron rails seem from a multitude of experiments to be much better than those of cast-iron, as they are more durable and cause less friction.

The Rocket was tried, weighing 4 tons and 5 cwt., to it there was attached a tender with water and coals, weighing 3 tons, 2 cwt. 8 quar. 2 lbs.; and two carriages loaded with stones, weighing 9 tons, 10 cwt. 3 qr. 26 lbs., making in all 17 tons. At full speed she moved at the rate of 30 miles in 2 hours, 6 minutes, 9 seconds, or 14 per hour at the end of stage, about 6 miles; and the greatest velocity was 29 miles per hour. The quantity of water used 92.6 cubic feet, and it required 11,7 lbs. of coke for each cubic foot of steam.

In the Rocket the boiler is cylindrical, with flat ends 6 feet long, and 3 feet 4 inches in diameter. . To one end of the boiler there is attached a square box as a furnace, 3 feet long by 2 feet broad, and about 3 feet deep-at the bottom of this box five bars are placed, and the box is entirely surrounded with a casting, except at the bottom and the

side next the boiler. Betwixt the casting and the box there is left a space of about 3 inches, which is kept constantly filled with water. The upper half of the boiler is used as a reservoir for steam; the under half being kept filled with water, and through this part copper tubes reach from one end to the other of the boiler, being open to the fire box at one end, to the chimney at the other; these tubes are 25 in number, each being 3 inches in diameter. The cylinders were each 8 inches in diameter, and one was at each side of the boiler; the piston had a stroke of 163 inches. The diameter of the large wheels was 4 feet 81 inches. The area of the surface of water, exposed to the radiant heat of the fire, was 20 square feet, being that sur rounding the fire box or furnace; and the surface exposed to the heated air or flame from the furnace, or what may be called communicative heat, is 117.8 square feet.

The average velocity of the Rocket may be stated at 14 miles per hour, and during one hour she evaporates 18.24 cubic feet of steam, with a consumpt of about 17.7 lbs. of coke for each cubic foot of water.

An empirical rule has been given for the ascertaining of the quantity of fuel necessary for steam carriages, which may be useful.

The weight of the load × 51.55+ weight of carriages

898

the quantity of coals required to carry one mile,--but a near approximation to the truth may be to allow 2 lbs. for every ton for one mile.

The flat rail, or

Iron railroads are of two descriptions. tram road, consists of cast iron plates about 3 feet long, 4 inches broad, and an inch or 1 inch thick, with a flaunch, or turned up edge, on the inside, to guide the wheels of the carriage. The plates rest at each end on stone sleepers of 3 or 4 cwt. sunk into the earth, and they are joined to each other so as to form a continuous horizontal pathway. They are, of course, double; and the distance between the opposite rails is from 3 to 4. feet, according to the breadth of the carriage or wagon to be employed The edge rail, which is found to be superior to the tram rail, is made either of wrought or cast iron; if the latter be used, the rails are about 3 feet long, 3 or 4 inches broad, and from 1 to 2 inches thick, being joined at the ends by cast metal sockets attached to the sleepers. The upper edge of the rail is generally made with a convex surface

to which the wheel of the carriage is attached by a groove made somewhat wider. When wrought iron is used, which is in many respects preferable, the bars are made of a smaller size, of a wedge shape, and from 12 to 18 feet long; but they are supported by sleepers, at the distance of every 3 feet. In the Liverpool railroad the bars are 15 feet long, and weigh 35 lbs. per lineal yard. The wagons in common use run upon 4 wheels of from 2 to 3 feet in diameter. Railroads are either made double, 1 for going and 1 for returning; or they are made with sidings, where the carriages may pass each other.-See M'Culloch's Dict. Table showing the effects of a force of traction of 100 pounds, at different velocities, on canals, railroads, and turnpike roads.*

2

3

30

4

3.66 55,500 39,400 14,400 10,800 1,800 1,350 4.40 38,542 27,361 14,400 10,800 1,800 1,350 5 13 28,316 20,100 14,400 10,800 1,800 1,350 5.86 21,680 15,390 14,400 10,800 1,800 1,350 5 7.33 13,875 9,850 14,400 10,800 1,800 1,350 8.80 9,635 6,840 14,400 10,800 1,800 1,350 10.26 7,080 5,026 14,400 10,800 1,800 1,350

6

7

8

3,848 14,400 10,800 1,800 1,350

11.73 5,420 9 13.20 4,282 3,040 14,400 10,800 1,800 1,350 10 14.66 3,468 2,462 14,400 10,800 1,800 1,350 13.5 19.9 1,900 1,350 14,400 10,800 1,800 1,350

The subject of steam vessels has been investigated by different engineers, on mathematical principles, but the calculations which their rules direct are by far too intricate for a work of this nature. We will, however, insert a statement of the proportions, &c., of several steamboats already made, which will doubtless be acceptable to the practical man, and those who wish to investigate the theory will find ample material in the work of Tredgold.

*The force of traction on a canal varies as the square of the velocity but the mechanical power necessary to move the boat is usually reckoned to increase as the cube of the velocity. On a railroad or turnpike, the force of traction is constant; but the mechanical power necessary to move the carriage, increases as the velocity.

15 ft. 0 in.

13 ft. 0 in.

12 ft. 6 in.

11 ft. 6 in.

Date of construction.. 1827

1825

1826

1826

1824

1824.

1826