I have a reference sheet for inorganic analysis which says that the confirmatory test for ferrous ions is as follows:
"Make a solution of the given salt (whose cation is to identified) and add potassium ferrocyanide [ potassium hexacyanidoferrate(II) ] solution to it.
If a dark blue precipitate is formed, then the presence of ferrous ions in the given salt is confirmed."
Chemically, what is the composition of this dark blue precipitate? Or is there a flaw in the test that I have specified?
If yes, then what is the real test and the chemical formula of the dark blue precipitate?