ed surfaces were omitted
and handholes substituted for the large access doors. A number of
boilers of this design were built but their excessive first cost, the
lack of adjustability of the structure under varying temperatures, and
the inconvenience of transportation, led to No. 7.

[Illustration: No. 7]

No. 7. In this boiler, the headers and water legs were replaced by
T-heads screwed to the ends of the inclined tubes. The faces of these Ts
were milled and the tubes placed one above the other with the milled
faces metal to metal. Long bolts passed through each vertical section of
the T-heads and through connecting boxes on the heads of the drums
holding the whole together. A large number of boilers of this design
were built and many were in successful operation for over twenty years.
In most instances, however, they were altered to later types.

[Illustration: No. 8]

[Illustration: No. 9]

Nos. 8 and 9. These boilers were known as the Griffith & Wundrum type,
the concern which built them being later merged in The Babcock & Wilcox
Co. Experiments were made with this design with four passages of the
gases across the tubes and the downward circulation of the water at the
rear of the boiler was carried to the bottom row of tubes. In No. 9 an
attempt was made to increase the safety and reduce the cost by reducing
the amount of steam and water capacity. A drum at right angles to the
line of tubes was used but as there was no provision made to secure dry
steam, the results were not satisfactory. The next move in the direction
of safety was the employment of several drums of small diameter instead
of a single drum.

[Illustration: No. 10]

This is shown in No. 10. A nest of small horizontal drums, 15 inches in
diameter, was used in place of the single drum of larger diameter. A set
of circulation tubes was placed at an intermediate angle between the
main bank of heating tubes and the horizontal drums forming the steam
reservoir. These circulators were to return to the rear end of the
circulating tubes the water carried up by the circulation, and in this
way were to allow only steam to be delivered to the small drums above.
There was no improvement in the action of this boiler over that of No.
9.

The four passages of the gas over the tubes tried in Nos. 8, 9 and 10
were not found to add to the economy of the boiler.

[Illustration: No. 11]

No. 11. A trial was next made of a box coil system, in which the water