clearly. Within the boiler, a, is placed the receiver, b, of pottery,
lead, or other material, leaving an annular space between it and the
boiler; this space is filled with water. The receiver, b, is furnished
with a series of pipes, in which steam or hot water circulates, to heat
the charge to the desired temperature. These pipes may be arranged
either in coils, as shown at d, Fig. 1, or vertically at d, Fig. 3. The
latter are provided with inner return pipes, so that any condensed water
accumulating at the bottom may be forced up the inner pipes by the
steam pressure and escape at the top. The vessel is charged through the
manhole, e, and the hopper, c, provided with a perforated cover, and is
discharged at the bottom by the valve, f, shown in Figs. 2 and 3. The
upper part of the boiler serves as a steam dome, and the pressure on the
liquid in the receiver and on the water in the annular space is thereby
maintained uniform. The necessary fittings for showing the pressure
in the vessel, water level indicator, safety valve, cocks for testing
solutions, etc., are of course added to the apparatus, but are not
indicated in the drawing. The arrangement appears to us to possess
considerable merit, and we shall refer to it again on another occasion,
after experiments have been made to test its efficiency.--_Engineering_.

[Illustration: IMPROVED DOUBLE BOILER.]

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THE GARDNER MACHINE GUN.