d or gaseous.

The gases of combustion evolved in the furnace above described are led
over the heating surfaces by two baffles. These are formed of cast-iron
baffle plates lined with special fire brick and held in position by tube
clamps. The front baffle leads the gases through the forward portion of
the tubes to a chamber beneath the drum or drums. It is in this chamber
that a superheater is installed where such an apparatus is desired. The
gases make a turn over the front baffle, are led downward through the
central portion of the tubes, called the second pass, by means of a
hanging bridge wall of brick and the second baffle, around which they
make a second turn upward, pass through the rear portion of the tubes
and are led to the stack or flue through a damper box in the rear wall,
or around the drums to a damper box placed overhead.

The space beneath the tubes between the bridge wall and the rear boiler
wall forms a pocket into which much of the soot from the gases in their
downward passage through the second pass will be deposited and from
which it may be readily cleaned through doors furnished for the purpose.

The gas passages are ample and are so proportioned that the resistance
offered to the gases is only such as will assure the proper abstraction
of heat from the gases without causing undue friction, requiring
excessive draft.

[Illustration: Partial Vertical Section Showing Method of Introducing
Feed Water]

The method in which the feed water is introduced through the front
drumhead of the boiler is clearly seen by reference to the illustration.
From this point of introduction the water passes to the rear of the
drum, downward through the rear circulating tubes to the sections,
upward through the tubes of the sections to the front headers and
through these headers and front circulating tubes again to the drum
where such water as has not been formed into steam retraces its course.
The steam formed in the passage through the tubes is liberated as the
water reaches the front of the drum. The steam so formed is stored in
the steam space above the water line, from which it is drawn through a
so-called "dry pipe." The dry pipe in the Babcock & Wilcox boiler is
misnamed, as in reality it fulfills none of the functions ordinarily
attributed to such a device. This function is usually to restrict the
flow of steam from a boiler with a view to avoid priming. In the Babcock
& Wilcox boiler its function is simply