ood construction, adapted for the narrow gauge. The
length of the wheel base of this engine is 12 feet 8-1/2 inches. There are
two cylinders, each 14-1/4 inches diameter and 21 inches stroke. The total
weight of the engine is 19 tons; and this weight is so distributed on the
wheels as to throw 8 tons on the leading wheels, 6 tons on the driving
wheels, and 5 tons on the hind wheels. The engine is made with outside
cylinders, and the cylinders are raised somewhat out of the horizontal line
to enable them better to clear the leading wheels.

656. _Q._--What are the dimensions of the boiler?

_A._--The interior of the fire box is 3 feet 7-1/4 inches wide by 3 feet
5-1/2 inches long, measuring in the direction of the rails. The area of the
fire grate is consequently 12.4 square feet. The bars are somewhat lower on
the side next the fire door than at the side next the tubes, and the mean
height of the crown of the fire box above the bars is 3 feet 10 inches. The
top edge of the fire door is about 7 inches lower than the crown of the
fire box. The fire box is divided transversely by a corrugated feather or
bridge of plate iron, containing water, about 3-1/2 inches wide, and of
about one-third of the height of the fire box in the centre of the feather,
and about two-thirds the height of the fire box at the sides where it joins
the sides of the fire box. The internal shell of the fire box tapers
somewhat upwards to facilitate the disengagement of the steam. It is about
2 inches narrower and shorter at the top than at the bottom; the water
space between the external and internal shell of the fire box being 2
inches at the bottom and 3 inches at the top.

657. _Q._--Of what material is the fire box composed?

_A._--The external shell of the fire box is formed of iron plates 3/8ths of
an inch thick, and the internal shell is formed of copper plates 1/4 inch
thick, but the tube plate is 3/4 inch thick. The fire grate is rectangular,
and the internal and external shells are tied together by iron stay bolts
3/4 inch diameter, and pitched about 4 inches apart. The roof of the fire
box is stiffened by six strong bars extending from side to side of the fire
box like beams, and the top of the fire box is secured to these bars, so
that it cannot be forced down without breaking or bending them.

658. _Q._--What are the dimensions of the barrel of the boiler?

_A._--The barrel of the boiler is 3 feet 7-1/2 inches in diameter, and 10
fee