Iodine Clock

German Hans Heinrich Landolt in 1892 for the first time cranked this experience, so he was called Landolt experience. Then the same experiment was nicknamed "the reaction of iodine hours." I will say that this is one of the most spectacular experiments. The solution was slowly becomes an amber color, then suddenly turns dark blue, then slowly regains colorless color; the process is repeated several times in a circle, eventually stopped on a dark blue color, and the liquid itself reeks of iodine. "
The reason is that during the first reaction produced by certain substances which, in turn, provoke the second reaction, and the process is repeated until exhaustion.

Source: mirfactov.com/