Pyrophoric iron h1>
In a beaker, dissolve 3.3 g of potassium oxalate in 25 ml of water. To this solution, pour hot solution of 5.6 g green vitriol (ferrous sulfate heptahydrate). After 15 minutes, the resulting precipitate was filtered, hang of a tube and the tube is annealed in an almost horizontal position. Black and precipitate gradually releases the water, after the precipitate turns black and does not release the water the tubes with a cotton swab and ignite until a powdered iron. When the contents of the tube are poured out, turns into rain sparks, especially visible in the darkened room.
The phenomenon is způsben large surface of iron allowing the oxygen present in the air easily oxidized iron oxide.