tephen Wilcox, in 1856, was the first to use inclined water tubes
connecting water spaces at the front and rear with a steam space above.
The first to make such inclined tubes into a sectional form was Twibill,
in 1865. He used wrought-iron tubes connected at the front and rear with
standpipes through intermediate connections. These standpipes carried
the system to a horizontal cross drum at the top, the entrained water
being carried to the rear.

Clarke, Moore, McDowell, Alban and others worked on the problem of
constructing water-tube boilers, but because of difficulties of
construction involved, met with no practical success.

[Illustration: Twibill, 1865]

It may be asked why water-tube boilers did not come into more general
use at an early date, that is, why the number of water-tube boilers
built was so small in comparison to the number of shell boilers. The
reason for this is found in the difficulties involved in the design and
construction of water-tube boilers, which design and construction
required a high class of engineering and workmanship, while the plain
cylindrical boiler is comparatively easy to build. The greater skill
required to make a water-tube boiler successful is readily shown in the
great number of failures in the attempts to make them.

[Illustration: Partial View of 7000 Horse-power Installation of Babcock
& Wilcox Boilers at the Philadelphia, Pa., Plant of the Baldwin
Locomotive Works. This Company Operates in its Various Plants a Total of
9280 Horse Power of Babcock & Wilcox Boilers]

REQUIREMENTS OF STEAM BOILERS

Since the first appearance in "Steam" of the following "Requirements of
a Perfect Steam Boiler", the list has been copied many times either word
for word or clothed in different language and applied to some specific
type of boiler design or construction. In most cases, although full
compliance with one or more of the requirements was structurally
impossible, the reader was left to infer that the boiler under
consideration possessed all the desirable features. It is noteworthy
that this list of requirements, as prepared by George H. Babcock and
Stephen Wilcox, in 1875, represents the best practice of to-day.
Moreover, coupled with the boiler itself, which is used in the largest
and most important steam generating plants throughout the world, the
list forms a fitting monument to the foresight and genius of the
inventors.

REQUIREMENTS OF A PERFECT STEAM BOILER