MILL. This word is now used in a general way as a name for almost all kinds of manufactories, as well as for s..,rinding-machinery; but we shall only de,scribe here the arrangements of an ordinary flour-mill. adding a brief notice of the edge-mill iu use for grinding oil-seeds and some other substances.
From time immemorial corn has been ground by a pair of stimes. The earliest and rudest handmills were no doubt somewhat like one sent home by Dr. Livingstone, the African traveler, from the banks of the Shire in South Africa. He describes it as "a mill such as Sarah used, when told by her lord to do the thing handsomely and in a hurry for the strangers—i. e., a big stone worn hollow by the operations of grinding. The upper stone is grasped by both hands, and the weight of the body brought down on it as it is shoved to the lower part The meal is made very fine." The next step in advance of this was the quern or handmill still iu use in the Shetland isles, the Farbes, and other places. The old quern scarcely differs from a pair of modern mill stones, except in the stones being small enough to allow of the upper one being turned by the hand instead of by wind, water, or steam power.
The millstones which are now all but universally used for grinding corn are made from bubr-stone, a form of silica like flint in hardness, but not so brittle. This rock is only found in abundance in the mineral basin of Paris and some adjoiuhig districts, and belongs to the tertiary formation. It is of a cellular texture, and is frequently full of silicified shells and other fossils. Millstones are usually from 4 to 6 ft. in diameter, and are each made up of a number of pieces strong,ly cemented and bound together with iron hoops. One 6 ft. in diameter, of fine quality, will cost about £50. The grinding surface of each stone is furrowed or glooi.ed, the ooves beitig cut perpendicularly on the one side, and with slope on the other, A pair of stoilea are, used' together, and both being furrowed exactly alike, the sharp edges of the grooves on the one come against those 013 the other, and so cut the grain to pieces.
Fig. 1 shows a section of a flour-mill reduced to its simplest elements. The millstones are at a, the lower of which is firmly fixed, it being a matter of importance to have this done securely; and the upper is made to revolve, ou a shaft which passes up through the lower one, at a speed of one hundred revolutions per minute, more or less. Motion is communicated by the spur-wheel b, which is driven by a water-wheel or other power. The corn, previously cleaned, is supplied to the millstones by means of the hopper c, 'connected with which there is a valve, d, for regulating the supply. Passing through a
hole• in the center of the upper millstone, it comes in between the two, where it is ground, and thrown out on all sides by means of the centrifugal force. The millstones are, of course, inclosed, and the flour passes down through the spout e, to the worm at f, which, while it cools the ground corn, carries it along to elevators g. These raise it up to the door on which the silk dressing-machine, ft, is placed. This is a cylinder, which was formerly made of wire-cloth of various degrees of fineness, and consequently ated the flour into different qualities--the finest passing through the first portion, the second passing throught the next, and so ou ; but no—part of it large enough in the openings to let through the bran, which passed out at the end. Silk is now preferred to wire-cloth for dressing the flour. Hoppers, i, are placed below the dre.ssing machine, by means of which the flour and bran are filled into sacks; No. 1 being fine flour; No. 2, seconds; and No. 3, bran.
One of the largest flour-mills in Great Britain is the one be longing to Messrs. Tod at Leith. It is about 150 feet long, 50feet broad, and 65 feet high. At one end of it is placed a steam engine of 350 horse—power, which works all the mathinery of the mill. This communi cates motion to a series of shafts and wheels occupying the ground-floor, belts beim,- used as much as possible for driving the wheels instead of spur gear, so as to avoid a slaking motion. On the second floor arc placed 36 pairs of millstones, arranged in two lines along the room, the wheat being supplied silently to them by centrifugal feeders. On the third floor are situated the hoppers for feedino. the millstones. The fourth floor contains iron rollers for partially crushing the wheat before being supplied to the millstones. This floor also contains silk aud wire dressing-machines. On the fifth floor are placed the first silk dressing-machine, and also smut-machiues for cleaning the wheat previous to grinding, which are somewhat similar to thrashing machines. The sixth and highest floor also contains smut-machines. All these machines are connected in the most skillful manner by means of elevators ascending through all the floors; and along each, where necessary, there runs, in a horizontal direction, an archimedean screw, so that the grain or the flour can be conveyed to any of the rnachines without the assistance of hand-labor.