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Page 31
In another form of kettle the seed is heated on a hot hearth, and on the
top of the hearth is a loose ring, within which a spindle revolves to
stir the seed. After the requisite temperature has been reached, the
ring is raised and the seed swept into the bags, which are made of
horse-hair. There is great loss of heat in this method, however, as the
seed is exposed to the atmosphere, which of course cools it.
We now come to the final operation, the mode of expressing the oil. The
screw press we do not need to describe, as it consists simply of two
plates, brought together by a screw, in the same way as the press used
for squeezing apples in the manufacture of cider, and the cheese press.
Let us look therefore at the stamper press. It consists of an iron box,
open at the top, at each end of which are two plates, capable of
containing between them a bag of seed which shall yield a cake weighing
9 lbs. To one of the inner plates of the box is attached a wedge, beside
which is inserted another filling up, and then the driving wedge is
introduced; and lastly, another block is let in between this wedge and
the other plate as soon as the bags have been placed vertically in the
press-box. A stamper of wood, worked by cambs on a revolving shaft, is
allowed to fall about 1 foot 10 inches, at the rate of fifteen strokes a
minute, for about six minutes. This stamper is 16 feet long by 8 inches
square, and falls on the head of the wedge, and drives it in to a level
at the top of the box. Another stamper is employed to drive down an
inverted wedge, so as to release the working one, and enable the
attendant to take out the cake. A press of this kind will turn out only
about 12 cwts. of cake a day.
We come now to the hydraulic press. This is certainly the most approved
invention that has yet been adopted, and it is simply a Bramah press
adjusted for the purpose. It has been in use for about thirty years,
though it was, of course, at first less skilfully and scientifically
constructed than it is now. In one of the earliest of these presses, the
box which contains the seed runs on a tramway in order to facilitate its
removal from the heating-kettle, so that each time the bags have to be
replenished the whole box has to be removed; and this causes no
inconsiderable loss both of power and time, for it has, when filled, to
be replaced on the ram and lifted bodily upwards in order to bring it
flush with the top of the press, which fits the press-box and acts as a
point of resistance. In this arrangement there are introduced only one
press and one set of small pumps.
The next press we come to is Blundell's, which is admitted to be by far
the most efficient in use to-day. Here there are two distinct presses,
or a double hydraulic press, fed by two pumps, one 2-1/2 inches and the
other 1 inch in diameter, both connected with the separate cylinders by
hydraulic tubing. The stroke of these pumps is 5 inches, and they make
thirty-six strokes a minute. The larger pump is weighted to 740 lbs. on
the square inch, and the smaller to 5540 the square inch. The diameter
of the rams is 12 inches, and the stroke 10 inches. Each press is fitted
to receive four bags of seed, and it produces 64 lbs. of cake at each
operation. After the heated seed has been placed in the bags, the
attendant proceeds to fill one press, and then he opens the valve
between the large pump and the charged press, which causes the ram to
rise till there is a pressure of forty tons, whereupon the safety-valve
of the large pump opens, and is kept so by a spring. While this
operation is going on, the attendant is occupied with filling the second
press; which completed, he opens the communication between the large
pump and the second press, taking care first to replace the
safety-valve. The ram of this press is then raised to the same height as
the other, after which the safety-valve rises a second time. The
attendant, as he closes the valve which opens the communication between
the large pump and the press, at the same time opens the valve between
the small pumps and the presses; and the pressure, amounting to about
300 tons, exerted by the small pump, is allowed to remain on the rams
for about seven minutes. From which it appears that, allowing three
minutes for emptying and charging the press, the process of expressing
the oil takes only three minutes in all; and it is done by this press in
this brief time in the most effectual manner. The oil, as it is
expressed, passes through the canvas and hair bags to a cistern, known
as the spill-tank, which is just large enough to contain the produce of
one day's working. The presses are worked by oil instead of water, as it
keeps both presses and pumps in better order. Each of them will produce
36 cwts. of cake per day of eleven hours, while the yield of oil is
about 14 cwts. The oil is pumped from the spill-tanks to larger ones,
capable of holding from 25 to 100 tons, where it remains for some time
in order to settle previously to being brought to the market.
I do not intend to enter into the relative merits of the various
presses, but content myself with having explained to you the manner in
which the oil is produced.
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