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 in hair or woollen bags and submitted to hydraulic pressure, by which a further portion of oil or fat is obtained (cf. Pressing, below). In the case of those animal fats which are intended for edible purposes, such as lard, suet for margarine, the greatest cleanliness must, of course, be observed, and the temperature must be kept as low as possible in order to obtain a perfectly sweet and pure material.

Pressing.—The boiling out process cannot be applied to small seeds, such as linseed and rape seed. Whilst the original method of obtaining seed oils may perhaps have been the same which is still used in India, viz. trituration of (rape) seeds in a mortar so that the oil can exude, it may be safely assumed that the process of expressing has been applied in the first instance to the preparation of olive oil. The first woman who expressed olives packed in a sack by heaping stones on them may be considered as the forerunner of the inventors of all the presses that subsequently came into use. Pliny describes in detail the apparatus and processes for obtaining olive oil in vogue among his Roman contemporaries, who used already a simple screw press, a knowledge of which they had derived from the Greeks. In the East, where vegetable oils form an important article of food and serve also for other domestic purposes, various ingenious applications of lever presses and wedge presses, and even of combined lever and wedge presses, have been used from, the remotest time. At an early stage of history the Chinese employed the same series of operations which are followed in the most advanced oil mills of modern time, viz. bruising and reducing the seeds to meal under an edge-stone, heating the meal in an open pan, and pressing out the oil in a wedge press in which the wedges were driven home by hammers. This primitive process is still being carried out in Manchuria, in the production of soja bean cake and soja bean oil, one of the staple industries of that country. The olive press, which was also used in the vineyards for expressing the grape juice, found its way from the south of France to the north, and was employed there for expressing poppy seed and rape seed. The apparatus was then gradually improved, and thus were evolved the modern forms of the screw press, next the Dutch or stamper press, and finally the hydraulic press. With the screw press, even in its most improved form, the amount of pressure practically obtainable is limited from the failure of its parts under the severe inelastic strain. Hence this kind of press finds only limited application, as in the industry of olive oil for expressing the best and finest virgin oil, and in the production of animal fats for edible purposes, such as lard and oleomargarine. The Dutch or stamper press, invented in Holland in the 17th century, was up to the early years of the 19th century

almost exclusively employed in Europe for pressing oil-seeds. It consists of two principal parts, an oblong rectangular box with an arrangement of plates, blocks and wedges, and over it a framework with heavy stampers which produce the pressure by their fall. The press box first consisted of strongly bound oaken planks, but later on cast-iron boxes were introduced. At each extremity of the box a bag of oil-meal was placed between two perforated iron plates, next to which were inserted filling-up pieces of wood, two of which were oblique, so that the wedges which exercised the pressure could be readily driven home. This press has had to yield place to the hydraulic press, although in some old-fashioned establishments in Holland the stamper press could still be seen at work in the ’eighties of the 19th century. The invention of the hydraulic press in 1795 by Joseph Bramah (Eng. pat., 30th April 1795) effected the greatest revolution in the oil industry, bringing a new, easily controlled and almost unlimited source of power into play; the limit of the power being solely reached by the limit of the strength of the material which the engineer is able to produce. Since then the hydraulic press has practically completely superseded all other appliances used for expression, and in consequence of this epoch-making invention, assisted as it was later on by the accumulator—invented by William George (later Lord) Armstrong in 1843—the seed-crushing industry reached a perfection of mechanical detail which soon secured its supremacy for England.

The sequence of operations in treating oil seeds, oil nuts, &c., for the separation of their contained oils is at the present time as follows: As a preliminary operation the oil seeds and nuts are freed from dust, sand and other impurities by sifting in an inclined revolving cylinder or sieving machine, covered with woven wire, having meshes varying according to the size and nature of the seed operated upon. This preliminary purification is of the greatest importance, especially for the preparation of edible oils and fats. In the case of those seeds amongst which are found pieces of iron (hammer heads amongst palm kernels, &c.), the seeds are passed over magnetic separators, which retain the pieces of iron. The seeds and nuts are then decorticated (where required), the shells removed, and the kernels (“meats”) converted into a pulpy mass or meal (in older establishments by crushing and grinding between stones in edge-runners) on passing through a hopper over rollers consisting of five chilled iron or steel cylinders mounted vertically like the bowls of a calendar. These rollers are finely grooved so that the seed is cut up whilst passing in succession between the first and second rollers in the series, then between the second and the third, and so