011-presscs.—In the East, where vegetable oil forms an important arti cle for food and for other personal and domestic purposes, various ingeni ous applications of lever-presses and of combined lever- and wedge-presses have been employed from the earliest times. The most ancient presses for extracting the oil from the seeds of various plants were those for express ing the oil of the olive, and were used in Palestine at a very early date. The preliminary crushing of the olive was done by means of the so-called "(Milian mill" (pl. 2, jig. 1). The oil-press in use at the present day in Syria and Palestine is substantially the same as that used by the Pliceni cians in the time of Solomon. It consists of two upright posts connected at the top by a heavy cross-piece or lintel. The mashed fruit, in straw bas kets, is placed on a bed-piece and the platen adjusted, upon which there is laid a beam whose ends slide in grooves on the inner faces of the posts as the beam is pressed clown by a lever above. This leverage requires the heavy lintel to resist the upward thrust of the lever. The oil-press of the Romans, which, according to Pliny, was an invention of Aristmus the Athenian, was of similar construction. Pliny describes in detail the apparatus and processes employed for obtaining olive-oil, and from him we learn that the Romans derived from the Greeks a knowledge of the screw-press, and that they used it to express oil from pulped olives.
In modern times the flax plant has constituted the largest source of supply of the oil-bearing seeds, but within the past few years cotton-seed has also been found to yield a large quantity of oil. The apparatus formerly used in Europe for expressing oil consisted of forms of wedge- and screw-presses and of the Dutch or stamping-press, an invention of the seventeenth cen tury, all of which have practically been superseded by the hydraulic press. The wedge-press is a powerful though somewhat crude machine. The crushed seeds are contained in hair bags, which are placed between ver tical perforated-iron cheek-plates. The space between the plates is occu pied by blocks and wedges, which are tightened by driving in the tighten ing wedge with a maul. Time is allowed for the oil to exude, when the pressure is removed by means of an inverted or loosening wedge. Screw presses were eventually substituted for the wedge-presses, and the Dutch press long played an important part in the oil industry, but the hydraulic press is now the main dependence.
Packing presses for compactly baling for transportation substances of considerable bulk, such as cotton, wool, hay, etc., arc of numerous vari eties. They are either of the screw, toggle, or hydrostatic type, and may be actuated by hand-, animal-, steam-, or other power. The simplest forum of packing-press consists essentially of a bed, vertical rods for the support of the press-head or enclosing sides, and a platen or follower, which is moved vertically downward, as in the screw-press (fi/. 9, fig. 8),
or upward, as in.the hydraulic press (fig. 9). Figure ro (Al. 6o) gives an example of a hay-baling press which is operated by horse-power, and which is fully described on page r9o.
Diferenlial-screw Packing-firess.—The power obtained by the use of a screw may be increased either by lengthening the lever or by increasing the number of threads in a given space—that is, by making them very fine. There is, however, a limit to the employment of either of these methods, for by increasing the length of the lever the machine becomes unwieldy, and the finer the threads the weaker they become. The dif ferential screw, invented by Dr. W. Hunter in 1781, obviates these diffi culties. It uses two screws of different pitch on the same shaft, the operation of which is analogous to that of the Chinese windlass (fi/. foS, fig. fo), whose barrel has two diameters, the rope unwinding from one as the other winds the rope. This principle is applied to the press shown in Figure S (fi/. 9). The presser or platen is urged downward by the screw having the greater pitch, while that with the smaller pitch draws back to an extent corresponding to its pitch. Thus during each revolu tion of the screw, instead of advancing the action through a space equal to the pitch of either of the threads, the platen is moved a distance equal only to the difference between the two pitches, and the mechanical power is therefore equal to that obtained from a single screw having a pitch equal to this difference. In this way pressure is obtainable to any extent within the practical limits of the difference between the pitches of the threads.
Toggle machine introduced as a mechanical substi tute for the hydraulic press is the Boomer press (fi/. 9, fig. 7). It consists of a combination of four levers or arms working upon toggle-joints, through which passes a right- and left-handed screw, whose rotation causes the two joints either to approach or to diverge from a central line according to the direction of such rotation, with a uniform motion. The sliding standard extends through the top frame or head-block, and keeps the pressure plate in its true horizontal position, controlling the power and preventing endwise motion of the screw. The entire pressure is not thrown on the threads of the screw, but is transmitted through the toggle-joints to the head-block, which is connected with the base by wrought-iron standards or posts. The power is applied by first running down the platen by the hand-wheel at the end of the screw until the heaviest pressure is attained, and the final pressure is applied by means of the lever and ratchet-wheel in the centre. It is claimed that with this machine one man is able to exert a power exceeding that of five men with the ordinary screw.