LOCOMOTIVE ENGINE.
409
merits that have been made in them, and the principal variations in construction
from other engines.
The general order of description will be, I. The Boiler, and the Manner of
Generating the Steam, with the means of supplying the boiler, of cleaning it out,
and of insuring its safety ; also of ascertaining the pressure of the steam, and the
quantity of water.
II. The Cylinders, and the Manner of using the Steam, with the mode of
supplying the cylinders with steam, and working the pistons and slide valves ; and
of moving the wheels and propelling the engine.
III. The Wheels, Framing, &c., of the Engine, with the springs, axle boxes,
and guides, &c., connected with the frame.
And IV. The Tender, for carrying coke and water to supply the boiler.
THE BOILER, AND THE MANNER OF GENERATING THE STEAM.
The boiler consists of several distinct parts ; the cylindrical portion A called
peculiarly the boiler, the external fire-box B communicating with it, the internal
fire-box C, containing the fire-grate D, and the tubes E communicating between
the internal fire-box and the smoke-box F, upon which is fixed the chimney G.
The Boiler AA (Plates LXXXIX. and CX.) is a cylinder 7 feet 6 inches long,
and 3 feet 6 inches in diameter outside; it is made of wrought iron plates five-six
teenths of an inch thick, lapping over each other, and joined together by iron
rivets seven-eighths of an inch in diameter and If inches apart, as shown at A
in fig. 5, which is a section of a joint, half Fig * 5 *
size. The rivets are inserted red hot and
contract in cooling, drawing the plates
forcibly together, and making a very close
joint.
The boiler is covered with wood a a (Plate XC.) one inch thick, put on in longi
tudinal staves, and bound round by the iron hoops bb, Plates LXXXIX. and CX.,
which are screwed together at the bottom ; this casing of wood is for the purpose
of retaining the heat, and preventing it from being carried off* by the air when
moving rapidly through it, wood being an imperfect conductor of heat.
The External Fire-Box B B is a box nearly square, 4 feet wide outside, and
3 feet 7\ inches long in the direction of the boiler, made of wrought iron plates
five-sixteenths of an inch thick, like those of the boiler; the bottom is 2 feet 1 inch
below the boiler, and the upper part is a semi-cylinder, concentric with the boiler,
as shown in the cross section, fig. 2, Plate XOII. The fire box is open at the
bottom, and has a circular opening cut in the front side, of the same size as
3 F