PREIINITE. A mineral of a green col or, one of the zeolit es, called after M.Prehn. PRESS. I. An instrument or machine of iron or wood by which any body is squeezed, crushed, or forced into a more compact form ; as, a Icinepress, cider press, or cheese-press. Any of the mechan ical powers may be used for this purpose, and also the hydrostatic pressure of wa ter. In the ordinary presses, the screw is employed as the power. Bydrostatic press.,) See BRAMAH'S PRESS.) 2. A. machine for printing ; a printing press. Great improvements have been lately made in the construction of presses. (See PRIM T IRO Pas e.) Press for compressing Flour orifeal into Casks. Every barrel ought to be of the size to contain 196 lbs. of meal or flour, when compressed. An empty barrel, with a &Ise one of the same size (that is, one without the top and bottom), placed above it, are first put upon the scales. The tare is made ; and the opposite end of the balance is charged with a weight of 196 lbs. Meal to that weight is then put into the two barrels standing in this position, as, in its uncompressed state, one barrel could not hold this quantity of meal. The barrels are then placed under the press, where a rammer, exactly fitting the barrel, is made to descend upon them ; the shaft of the rammer mounts and de scends between two snuffling-boards, which serve to guide it. It is furnished with two small beams, which are fixed in a sort ofpivot, and which form the ex tremity ora large lever. When this lever is lowered, it causes the rammer to de scend upon the meal, and a sufficient de gree of pressure is thus produced. Bnt, should it be required to augment the power of the lever, this can be done by applying another lever to assist in work ing the large lever. When the pressure is finished the lever is raised, and the false barrel, which is now empty, is re moved.
Copper-plate, or Rolling-Press. The rolling-press, which is employed in near ly every species of copper-plate printing, is divided into two parts, the body and the carriage. The body consists of two wooden cheeks, placed perpendicularly on a stand or foot, which sustains the whole press. From the foot, likewise .
rise four other perpendicular pieces, pin ed by cross or horizontal ones, which serve to sustain a smooth even plank or table, about four feet and a half long, two feet and a half broad, and an inch and a half thick. Into the cheeks go two wood
en cylinders or roller. about six inches in diameter, borne up at each end by the cheeks, whose ends, which are lessened to about two inches diameter, and called trunnions, turn in the cheeks about two pieces of wood in form of half moons, lined with polished iron to facilitate their motion. Lastly, to one of the trunnions of the upper roller is fastened a cross, consisting of two levers, or pieces of wood, traversing each other, the arms of which cross serve instead of the bar or handle of the letter-press, by turning the upper roller, and, when the plank is between the two rollers, giving the same motion to the under one, by drawing the plank forward and backward. The ink usually employed is a composition made of the stones of peaches and apricots, the bones of sheep, and ivory, all well burnt, and called Frankfort Black, mixed with nut oil that has been well boiled ; the two be ing ground together on a marble slab, in the same manner as painters grind their colors.
A small quantity of this ink is taken on a rubber, made of linen rags, strongly bound about each other, and then smear ed over the whole face of the plate, as it lies on a grate over a charcoal lire. The plate being sufficiently inked, it is wiped over with a dirty rag, then with the palm of the left hand, then with that of the right ; and to dry the hand, and forward the wiping, it is rubbed, from time to time, on whiting. In wiping the plate perfectly clean, but without taking the ink out of the engraving, consists the skill of the workman. The plate, thus prepared, is laid on the plank of the press, and over the plate is laid the paper, well moistened to receive the impression; and over the paper two or three folds of flan nel. The arms of the cross are then pull ed, and the plate, with its furniture, is passed through between the collars, which, pinching very strongly, press the moistened paper into the strokes of the engraving, and it absorbs the ink from them.