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The mystery of magnetic doors.

The mystery of the magnetic doors

According to Chinese legend, a tomb located near the town of Sian and belonging to the first emperor of the Ch'in dynasty (221-206 BC) had a door that could not be cut with iron swords because the door magnetically attracted the iron. Moreover, in a newly discovered volume of an encyclopedia compiled in China in 1406, scholars found passages indicating that the gates of a nearby palace were also made of magnetic stone: "Warriors wearing iron armor were detained or attracted and could not pass through."

Now scientists think they have a clue to the origin of this magnetic stone. In a letter appearing in the Feb. 13 NATURE, Tai Li-Chi of the Research Institute of Iron and Steel in Beijing reports that a colleague discovered that the sand along the banks of the Wei River, which passes by Sian, can be used as ferrite material with good magnetic properties. Tai analyzed the sands and found that they contain magnetite and other magnetic oxides. "The quality of the material is not inferior to the synthetic oxides used in the manufacture of ferrite in modern industry," he says. But, he concludes, "we have not yet found any direct evidence that this magnetic sand was [indeed] used in ancient times."
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Title Annotation:magnetic sand discovered in China
Publication:Science News
Date:Mar 8, 1986
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