Liesegang phenomenon - Lieseganggensho

This refers to the ring pattern that occurs as a result of a reaction inside a solid gel, discovered by RE Liesegang in 1896. If gelatin containing potassium dichromate is spread evenly on the surface of a flat glass plate and a few drops of an aqueous solution of silver nitrate are dropped into the center, the two reagents will react to produce a reddish-brown precipitate of silver chromate, which will form a concentric ring pattern centered on the point of application. If the same experiment is performed using an upright test tube, layers will appear above and below the test tube. Various theories have been put forward for this phenomenon, in addition to an explanation that attributes the cause to the diffusion speed of the reactants.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

1896年，R.E. Liesegangの見いだした，固体ゲル内での反応の結果生じる環紋をいう．二クロム酸カリウムを含むゼラチンを，平らなガラス板の表面に一様に塗り，その中央へ数滴の硝酸銀水溶液を滴下すると，両試薬は反応して赤褐色のクロム酸銀の沈殿を生じるが，これは滴下点を中心として同心円形の環紋となる．また，同様のことを直立した試験管を用いて行うと，試験管内に上下に層状となって現れる．この現象に対して，反応物質の拡散速度に原因を求めた説明のほか，いろいろな説が提出されている．

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