As we know, the wheel was invented by the Sumerians. They are also the authors of the first cuneiform texts in history. Five thousand years ago, scholars in the area of modern Baghdad were scribbling signs of writing with a pointed reed on a clay plane. Two of these discoveries were almost enough to stimulate Emile Berliner's creative imagination for his main project. The famous native of Lower Saxony modernized Edisson's phonograph, uncomfortable for widespread use, into the most popular consumer "toy" of the early 20th century: the gramophone. "He placed the "wheel" horizontally, and applied the needle not to the letters, but to the sound record.
Berliner found the crucial clue near his native Hanover. To the south of it, at the foot of the pine-forested Harz mountain range, is Germany's smallest university town, a center of mining science and at the same time a resort place - Clausthal. It was there in 1853 (34 years before the patent for the gramophone was granted) that the first rundgerd (round table - from German) was built.
The device, which resembles a music player, is designed for ore enrichment. A mixture of water and ore grains in the waste rock is fed from above into the center of the disk. As it rotates on the axis of the central shaft, the particles of valuable, heavier veined rock are blown to the outer edge of the circle. There they are removed to be used as raw material for the smelting works.
The main structural element of the rundgerd differs from the base plate of the electrophone and its ancestor, the gramophone, in that it is slightly tapered, but the 6 percent slope is not noticeable. Speed and size, of course, are also different - the miners' device is 5 meters across and makes one revolution in 2.5-5 minutes, while the music disc takes less than a second to do so (the standard is 78 revolutions per minute). But both are covered with felt (slimpats, mats under the record made of felt, are probably the most common today).
By 1870 the circular dressing tables had already proven themselves in the enterprises of the Harz, and the St. Petersburg Mining Institute acquired a working model of the device for training purposes. Today it is on display in its museum.
At modern mining and processing plants, it has long been used mostly not rundgers, but flotation machines, which are not tables, but baths. At one time, the prototype of the gramophone was quite serious in increasing the efficiency of the mining and concentrating process. It allowed to process the most finely crushed sands and schlichs continuously. Therefore, it was widely used in Central Europe until the 1920s.
This is not the end of his story, though. Our parallel between the two devices, mountain and sound, has a postscript. Mechanical music players were all but superseded by digital CDs by the late 1990s, but soon returned to the mainstream. In 2021, gramophone records again wrested first place from CDs in the U.S. in sales, taking 50.4 percent of the market, about 42 million units. Rundgerds haven't fallen into oblivion, either. In 2012, for example, the St. Petersburg Mining University defended a thesis on improving the efficiency of enrichment of fine ore fractions using centrifugal separation on the basis of the same round tables. Of course, significantly improved.
