. A dictionary of arts, manufactures and mines : containing a clear exposition of their principles and practice. , is quite analogous to the gunpowder-mill representedin fig. 531, page 636. Some hoop the stones with an iron rim, but others prefer, and Ithink justly, the rough surface of granite, and dress it from time to time with hammers,as it becomes irregular. These stones make from 30 to 36 revolutions upon theirhorizontal bed of masonry or iron in a minute. The centre of the bed, where it is per-forated for the passage of the strong vertical shaft which turns the stones, is enclosed bya c
. A dictionary of arts, manufactures and mines : containing a clear exposition of their principles and practice. , is quite analogous to the gunpowder-mill representedin fig. 531, page 636. Some hoop the stones with an iron rim, but others prefer, and Ithink justly, the rough surface of granite, and dress it from time to time with hammers,as it becomes irregular. These stones make from 30 to 36 revolutions upon theirhorizontal bed of masonry or iron in a minute. The centre of the bed, where it is per-forated for the passage of the strong vertical shaft which turns the stones, is enclosed bya circular box of cast iron, firmly bolted to the bed-stone, and furnished with a box serves to prevent any seeds or powder setting into the step or socket, andobslructins; the movement. The circumference of the mill-bed is formed of an uprightrim of oakplank, bound with iron. There is a rectangular notch left in the edge of thebed, and correspondin? part of the rim, which is usually closed with a slide-plate, and-s opened only at the end of the operation, to let the pasty seed-cake be turned out by. 906 OILS, UNCTUOUS. the oblique arm of the bottom scraper. The two parallel stones, which are set near eachother, and travel round their circular path upon the bed, grind the seeds not merely bytheir weii^ht, of three tons each, but also by a rubbing motion, or attrition ; because theirperiphery being not conical, but cylindrical, by its rolling upon a plane surface, must atevery instant turn round with friction upon their resting points. Strong cast-iron boxesare bolted upon the centre of the stones, which by means of screw clamps seize firmly thehorizontal iron shafts that traverse and drive them, by passing into a slit-groove thevertical turning shaft. This groove is lined with strong plates of steel, which wear rap-idly by the friction, and need to be frequently renewed. The seeds which have been burst between the rolls, or in the mortars of the Dutchmills, are to be sp
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