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Page 30
The system of pestle and mortar was also in use, but as the process was
necessarily very slow, this method was seldom resorted to. An
improvement on this system was invented by a Mr. Herbert, whose design
it had been to construct a powerful and efficient machine which should
combine cheapness and simplicity. It consisted of three pieces of wood,
viz., an upright piece fixed in the ground, from the lower and upper
extremities of which there projected the two other pieces, the top one
attached to the joint of a long horizontal lever, and the lower one to
the joint of a vertical one. The fixed upright post and the horizontal
lever formed the press. The bag of pulp being put between the upright
one and the vertical, the pressure was obtained by suspending a negro or
a weight from the lever.
In another press of the same or a similar kind, the bags were placed in
a horizontal frame, and a loose beam of wood pressed down on it by a
lever.
Another form of press had cambs and wedges; also a modification of it by
Mr. Hall of Dartford, who applied the pressure by means of a
steam-cylinder. The cambs are arranged alternately, so that one is
filled while the other is being pressed. This brief notice will suffice
to give an idea of such machines as are wrought by lever pressure.
We pass on, therefore, to later inventions and improvements.
First, The Dutch or _stamper_ press, invented in Holland; second, the
_screw_; and, third, the _hydraulic_:--
(1.) _The stamper press_ is something like a beetling-machine, in which
wedges are driven in between the bags, containing, of course in a
bruised condition, the seed to be pressed.
(2.) _The screw press_ has an ordinary square-threaded screw, and it
acts in the same way as press for making cider or cheese.
(3.) _The hydraulic press_. Here the pressure is produced by means of a
piston driven up by the force of water, the immense power of which is,
in great part, due to its almost total incompressibility. This is by far
the most perfect form of press. Its power must be familiar to all who
remember the lifting of the tubes of the Britannia Bridge, and the
_launching of the Great Eastern_.
An oil-mill is in form something like a flour-mill. The operation
begins at the top, where the seed is passed through a flat screw or
shaker and then through a pair of rollers, which crush it. These rollers
are of unequal diameter, the one being 4 feet, and the other 1 foot; but
they are both of the same length, 1 foot 4 inches, and make fifty-six
revolutions in a minute. By this arrangement it is found the seed is
both better bruised and faster than when, as was formerly the case, the
rollers were of the same diameter. A pair of rollers will crush 4-1/2
tons of seed in eleven hours, a quantity enough to keep two sets of
hydraulic presses going.
After the seed is crushed in this way, it is passed under a pair of edge
stones. These stones weigh about seven tons, are 7 feet 6 inches in
diameter and 17 inches broad, and make seventeen revolutions a minute.
If of good quality, they will not require to be faced more than once in
three years, and they will last from fifteen to twenty. They are fitted
with two scrapers, one for raking the seed between the stones, the other
for raking it off at the proper period. One pair of stones will grind
seed sufficient for two double hydraulic presses, and the operation
occupies about twenty-five minutes. The seed is now crushed and ground,
but before it is passed on to the press it is transferred to the
heating-kettle.
The heating-kettle is composed of two cylindrical castings, one fitting
loosely into the other, so that a space is left between them for a free
circulation of steam all round both the sides and bottom of the interior
vessel. The internal casting is again divided horizontally into two
partitions, one above the other therefore, by two plates, between which
also there is a space left for the admission and circulation of steam;
and a communication is kept up between the upper compartment and the
under by means of a stripping valve. Besides this, there is a
communication from the internal kettle through the external one, and
also a shaft passes between the two horizontal parts to give motion to
the stirrer, which revolves thirty-six times a minute. A cover encloses
the top, and it is through this the vessel is charged. The upper portion
is filled first, where the contents introduced are allowed to remain ten
or fifteen minutes, after which the valve is opened and the whole falls
into the lower kettle, where it is kept till wanted. The seed is then
taken away from the lower kettle by an opening, and bestowed in bags of
sufficient size to make a cake of 8 lbs. weight after the oil is pressed
out of it. Indeed, the compartments of the heating-kettle are of a size
to contain enough to charge one side of a hydraulic press. These,
therefore, are so constructed as to render the operation continuous, the
upper one being discharged into the under as soon as its contents are
withdrawn to the press. The seed is heated to the temperature of 170
degrees Fahr., when it is drawn off and placed in the bags.
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