Jasper Republican, Volume 1, Number 4, Rensselaer, Jasper County, 9 October 1874 — Light Observed in Grinding Hard Stones. [ARTICLE]

Light Observed in Grinding Hard Stones.

• At the agate-polishing establishments of Oldenburg, Germany, a phenomenon has been observed for the past century that has as yet, perhaps, attracted too little attention from scientific men. Under very powerful friction, such as can only be produced by the machinery at these works, hard stones become splendidly luminous and transparent through•out. In this establishment the axis of an undershot water-wheel reaches into the grinding-room, where four or five grindstones rotate over each is brought a gutter, so that a constant small stream of water pours upon the stone. The grindstones themselves are entirely faultless. They are about five feet in diameter, and make three revolutions in a second, so that the grinding surface that passes the object pressed against it amounts to thirty-two English miles per hour. When grinding the workman lies on his belly, his chest on a semi-cylindri-cal hollowed stool, his feet stretched out behind, braced against a post fixed in the floor. With both hands he presses the stone to be polished firmly against the grindstone, bringing his whole weight to bear Upon it. The muscular strength to bear is very great, and the work is performed with intermissions of equal times of rest and work. Some experiments were made in this workshop by Noggerath in broad daylight. He observed that as long as a stone of the hardness of quartz was pressed against the revolving grindstone there was produced an intense red light, which at the same time radiated around the object and emitted numerous sparks. This experience was the same with all hard stones, which appear almost like red-hot iron, and it really looks as if the hands must be severely burnt. All the stones become warm in grinding, but not very hot. Chalcedony gave a magnificent fiery red light; chrysopase a little red light; rock crystal a beautiful rose red;

coralline a superb red light, the color being evidently, increased by the natural hue of the stone. Amethyst gave a pale violet, while numerous opaque stones gave no light at all.