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