Lectures on popular and scientific subjects

by 14th earl of James Sinclair Caithness

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.

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.