ent, it had the
basic defect of keeping the smoke low and close to the train. This was a
great nuisance to passengers, as the low trailing smoke blew into the
cars. If the exhaust had been allowed to blast straight out the stack
high into the air, most of the sparks would have burned out before
touching the ground.

[Illustration: Figure 21.--"PIONEER" ON EXHIBIT in old Arts and
Industries building of the Smithsonian Institution. In this view can be
seen the bonnet screen of the stack and arrangement of the boiler-frame
braces and other details not visible from the floor. (Smithsonian photo
48069A.)]

[Illustration: Figure 22.--"JENNY LIND," SISTER ENGINE of the _Pioneer_,
shown here as rebuilt in 1878 for use as an inspection engine. It was
scrapped in March 1905. (_Photo courtesy of E. P. Alexander._)]

[Illustration: Figure 23.--CYLINDER head with valve box removed.]

[Illustration: Figure 24.--BOTTOM of valve box with slide valve
removed.]

[Illustration: Figures 25 and 26.--CYLINDER with valve box removed,
showing valve face.]

FRAME

The frame of the _Pioneer_ defies an exact classification but it more
closely resembles the riveted- or sandwich-type frame than any other
(figs. 18, 27). While the simple bar frame enjoyed the greatest
popularity in the last century, riveted frames were widely used in this
country, particularly by the New England builders between about 1840 and
1860. The riveted frame was fabricated from two plates of iron, about
5/8-inch thick, cut to the shape of the top rail and the pedestal. A bar
about 2 inches square was riveted between the two plates. A careful
study of photographs of Hinkley and other New England-built engines of
the period will reveal this style of construction. The frame of the
_Pioneer_ differs from the usual riveted frame in that the top rail is
1-3/4 inches thick by 4-1/8 inches deep and runs the length of the
locomotive. The pedestals are made of two 3/8-inch plates flush-riveted
to each side of the top rail. The cast-iron shoes which serve as guides
for the journal boxes also act as spacers between the pedestal plates.

The bottom rail of the frame is a 1-1/8-inch diameter rod which is
forged square at the pedestals and forms the pedestal cap. The frame is
further stiffened by two diagonal rods running from the top of each
truck-wheel pedestal to the base of the driving-wheel pedestal, forming
a truss. Six rods, riveted to the boiler shell and bolted to the