Scientific American Supplement, No. 623 | Page 2

within the
frame, forces a certain quantity of cold air at every revolution into the
driving cylinder. The piston of this pump is actuated by the connecting
rod, G', jointed to the lever, F', which receives its motion from the rod,
F. A slide valve, _b'_, actuated by a cam, regulates the entrance of the
cold air into the pump during suction, as well as its introduction into
the cylinder. There is a thrust upon the piston during its upward travel,
and an escape of hot gas through the eduction valve, h, during the
downward travel.
The cylinder is in two parts, C and C'. The piston, which is very long,
rubs at its upper end against the sides of the cylinder, C. The lower end
is of smaller diameter, and leaves an annular space between it and the
cylinder. The grate is at the bottom of the cylinder, C'. The sides of the
cylinder at the level of the fire box are protected with a lining of
plumbago. When the piston is at the bottom of its travel, the eduction
valve closes. The slide valve, _b'_, establishes a communication
between the pump chamber and the cylinder. The air contained in the
pump is already compressed in the latter to a pressure of nearly a
kilogramme at the moment of the communication. This air enters the
cylinder, and the communication between the latter and the pump
continues until all the air is forced into the driving cylinder, the piston
of the pump being at the bottom of its travel, and that of the cylinder
about midway.
[Illustration: BENIER'S HOT AIR ENGINE.]
The air forced by the pump piston enters the cylinder through two
conduits, one of which leads a portion of it toward the top of the
cylinder, and the other toward the bottom. The lower conduit
debouches under the grate, and the air that passes through it traverses
the fire box, and the hot gas fills the cylinder. The conduit that runs to
the top debouches in the cylinder, C, at the lower limit of the surface
rubbed by the piston. The air that traverses this conduit is distributed
through the annular space between the piston and cylinder. The hot gas
derived from combustion can therefore never introduce itself into this

annular space, and consequently cannot come into contact with the
rubbing surfaces of the cylinder and piston.
As the quantity of air introduced at every stroke is constant, the work
developed at every stroke is varied by regulating the temperature of the
gas that fills the cylinder. When the temperature falls, the pressure, and
consequently the work developed, diminishes. This result is obtained
by varying the respective quantities of air that pass through the fire box
and around the piston. In measure as less air passes through the fire box,
the quantity that passes around the piston augments by just so much,
and the pressure diminishes. A valve, _n'_, in the conduit that runs to
the fire box is controlled by the regulator, L', in the interior of the
column. When the work to be transmitted diminishes, the regulator
closes the valve more or less, and the work developed diminishes.
The coke is put by shovelfuls into a hopper, I. Four buckets mounted
upon the periphery of a wheel, I', traverse the coke, and, taking up a
piece of it, let it fall upon the cover, J, of the slide valve, j, whence it
falls into the cavity of the latter when it is uncovered, and from thence
into the conduit, _c'_, of the box, _j'_, when the cavity of the valve is
opposite the conduit. From the conduit, _c'_, the coke falls upon the
grate.
A small sight hole covered with glass, in the cover, J, permits the grate
to be seen when the cavity of the valve is opposite _c'_.
As in gas engines, a current of water is made to flow around the
cylinder, C', in order to keep the sides from getting too hot.
In order to set the engine in motion, we begin by opening the bottom, C,
of the cylinder, C', to clean the grate. This done, we close C and
introduce lighted charcoal through the conduit, _c'_ (the valve being
open). The valve is put in place, two or three revolutions are given to
the fly wheel, and the motor starts. The feeding is afterward done with
coke.
The parts that transmit motion operate under conditions analogous to
those under which the same parts of a steam engine do. The air pump

sucks and forces nothing but cold air, and nothing but cold air passes
through the distributing slide valve. The pump and valve are therefore
rendered very durable. The piston and cylinder, at the points where
friction exists, are at a temperature