A. NTILLSTONV-AI I LIS.
The one-stone mill, driven by water or wind, proved a great advance over the Mosaic mealing-mortars and mills which had been used for centuries. The time had not come for developing and employing the full mill-power of running streams or forceful winds, or the wonderful energy of steam. The mill-builders of the past appear to have had no conception of the superior advantages of large water- and wind-wheels or of the systematic distribution of their power, but confined themselves to the primitive idea of driving one millstone by one wheel, and of bolting with one reel. Most of the mills in the East, in Europe, and in America were arranged on this plan up to about the middle of the last century, and some such are still in use. During the days of Smeaton, the eminent English millwright, mills began to be planned and constructed on what are now denominated "engineering methods," which soon led the way to the perfection of mill ing-plants now everywhere employed.
Elemenlary Principles of the time of the earliest revolving millstone to the present, certain essential elementary principles and mechanical devices of construction have been embodied in the building of the mill—namely, the fixed lower stone, the revolving upper stone, and the horizontal and nearly parallel grinding surfaces of the stones. The runner stone is fixed to, or hung loosely on, the top of a vertical spindle passing through the centre of the lower stone, and the foot of the spindle is carried on a bearing so devised that it may be raised or lowered while in motion, for the purpose of regulating the space between the grinding surfaces of the two stones. Moreover, means are provided for regulating the feed; a speed of rotation is established suf ficient to throw out the ground material; and the millstones are enclosed in a case, from which the meal is delivered by a pipe. For separating the finer meal from the coarser particles and the bran, a hand-sieve was until quite recently the only device employed.
is highly probable that in the early history of milling the process of bolting was not resorted to, and that unbolted flour was used for baking. When it seemed desirable to secure the finer products of the grain by excluding the bran, a sieve moved by hand was employed for the pur pose. A sieve in the form of an extended bag, to receive the meal from the stones and to be turned and shaken by the machinery, was first adopted in the beginning of the sixteenth century. In r5o2 machinery for bolting in mills was first introduced and employed at Zwickau by Nicholas Boller.
Dress of ingenuity has been displayed upon the draft and dress of millstones (6/. 4, jigs. 8–'3), about which the opinions and practice of millers differ widely. Dress is the system whereby the face or grinding surface of the stone is prepared by lands and furrows. The grooves which expedite the grinding action are termed "furrows," and the level surfaces between the latter arc the " lands." Grinding is partly on the principle of shearing; and to effect this object the "furrows" on the faces of the millstones arc cut obliquely to the radius. Refinements of mechan ism, however, arc apt to lead too far in one direction; for example, Professor Kick states that, in 1873, Franz Schmid of Lanzendorf experimented by reversing the direction of the runner stone, but did not observe any particular difference in the quantity or quality of the material ground.
The (pl. 4, fig. 7) is a tool for dressing the face of millstones after they have become smooth by use; the dressing gives to the burrs a furrowed surface adapted to grinding. The illustration shows one of the many forums of picks devised for the purpose; it is a lozenge-shaped bar of steel with a chisel-edge at each end, and is made exceedingly hard and tough by skilful forging and tempering. The handle, which is usually of hard wood, has a split head and is bound with metal.