h when heated. In addition to the crown
bars, which strengthen the crown sheet, the boiler is further
strengthened by stay bolts and braces located in the wagon top over the
firebox, where the boiler had been weakened by the large hole necessary
for the steam dome. This boiler is a remarkably light, strong, and
compact structure.

BOILER FITTINGS

Few boiler fittings are found on the _Pioneer_ and it appears that
little was done to update the engine with more modern devices during its
many years of service. With the exception of the steam gauge, it has no
more boiler fitting than when it left the builder's shop in 1851.

The throttle valve is a simple slide valve and must have been primitive
for the time, for the balance-poppet throttle valve was in use in this
country previous to 1851. It is located directly below the steam dome
even though it was common practice to place the throttle valve at the
front of the boiler in the smokebox. Considering the cramped condition
inside the smokebox, there would seem to be little space for the
addition of the throttle valve; hence its present location. The dry pipe
projects up into the steam dome to gather the hottest, driest steam for
the cylinders. The inverted, funnel-like cap on the top of the dry pipe
is to prevent priming, as drops of water may travel up the sides of the
pipe and then to the cylinders, with the possibility of great damage.
After the steam enters the throttle valve it passes through the front
end of the valve, through the top of the boiler via the dry pipe (fig.
18), through the front tube sheet, and then to the cylinders via the
petticoat pipes. The throttle lever is a simple arrangement readily
understood from the drawings. It has no latch and the throttle lever is
held in any desired setting by the wingnut and quadrant shown in figure
18. The water level in the boiler is indicated by the three brass cocks
located on the backhead. No gauge glass is used; they were not employed
in this country until the 1870's, although they were commonly used in
England at the time the _Pioneer_ was built.

While two safety valves were commonly required, only one was used on the
_Pioneer_. The safety valve is located on top of the steam dome.
Pressure is exerted on the lever by a spring balance, fixed at the
forward end by a knife-blade bearing. The pressure can be adjusted by
the thumbscrew on the balance. The graduated scale on the balance gave a
general but uncertai