hragms cast in them, but sometimes steel
has been employed, the bottoms being closed by a riveted steel plate,
and the diaphragms being made of the same material. The headers are
bolted to socket-pieces which are riveted to the bottom of the
steam-chest, so that any element may be easily removed. The tube-holes
are accurately bored, at an angle to suit the inclination of the
tubes, through both the front and back of the headers and through the
diaphragm, those in the header walls being slightly conical. The tubes
themselves, which are made of seamless steel, are of peculiar
construction. The lower or back ends are reduced in diameter and
screwed and fitted with cap-nuts which entirely close them. The front
ends are thickened by being upset, and the parts where they fit into
the header walls and in the diaphragm are carefully turned to gauge.
The upper and lower parts of the tubes between these fitting portions
are then cut away, the side portions only being retained, and the end
is termed a "lanterne." A small water-circulating tube of thin sheet
steel, fitted inside each generating tube, is open at the lower end,
and at the other is secured to a smaller "lanterne," which, however,
only extends from the front of the header to the diaphragm. This
smaller "lanterne" closes the front end of the generating tube. The
whole arrangement is such that when the tubes are in place only the
small inner circulating tubes communicate with the space between the
front of the header and the diaphragm, while the annular spaces in the
generating tubes around the water-circulating tubes communicate only
with the space between the diaphragm and the back of the header. The
steam formed in the tubes escapes from them into this back space,
through which it rises into the steam-chest, whilst the space in the
front of the header always contains a down-current of water supplying
the inner circulating tubes. The tubes are maintained in position by
cross-bars, each secured by one stud-bolt screwed into the header
front wall, and each serving to fix two tubes. The products of
combustion ascend directly from the fire amongst the tubes, and the
combustion is rendered more complete by the introduction of jets of
high-pressure air immediately over the fire, as in the "Belleville"
boiler.

Durr.

The "Durr" boiler, in use in several vessels in the German navy, and
in a few ve