thering pipes, and these latter in
turn to a steam drum.

In 1822, Jacob Perkins constructed a flash boiler for carrying what was
then considered a high pressure. A number of cast-iron bars having 1-1/2
inches annular holes through them and connected at their outer ends by a
series of bent pipes, outside of the furnace walls, were arranged in
three tiers over the fire. The water was fed slowly to the upper tier by
a force pump and steam in the superheated state was discharged to the
lower tiers into a chamber from which it was taken to the engine.

[Illustration: Joseph Eve, 1825]

The first sectional water-tube boiler, with a well-defined circulation,
was built by Joseph Eve, in 1825. The sections were composed of small
tubes with a slight double curve, but being practically vertical, fixed
in horizontal headers, which headers were in turn connected to a steam
space above and a water space below formed of larger pipes. The steam
and water spaces were connected by outside pipes to secure a circulation
of the water up through the sections and down through the external
pipes. In the same year, John M'Curdy of New York, built a "Duplex Steam
Generator" of "tubes of wrought or cast iron or other material" arranged
in several horizontal rows, connected together alternately at the front
and rear by return bends. In the tubes below the water line were placed
interior circular vessels closed at the ends in order to expose a thin
sheet of water to the action of the fire.

[Illustration: Gurney, 1826]

In 1826, Goldsworthy Gurney built a number of boilers, which he used on
his steam carriages. A number of small tubes were bent into the shape of
a "U" laid sidewise and the ends were connected with larger horizontal
pipes. These were connected by vertical pipes to permit of circulation
and also to a vertical cylinder which served as a steam and water
reservoir. In 1828, Paul Steenstrup made the first shell boiler with
vertical water tubes in the large flues, similar to the boiler known as
the "Martin" and suggesting the "Galloway".

The first water-tube boiler having fire tubes within water tubes was
built in 1830, by Summers & Ogle. Horizontal connections at the top and
bottom were connected by a series of vertical water tubes, through which
were fire tubes extending through the horizontal connections, the fire
tubes being held in place by nuts, which also served to make the joint.

[Illustration: Stephen Wilcox, 1856]

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