Invisible letterings show after adding a brown solution
name: Demonstration of the reactions of iron (III) chloride with potassium thiocyanate and potassium ferrocyanide
Solutions of potassium thiocyanate and potassium ferrocyanide are colorless, and letterings made with these solutions are invisible.
Iron (III) chloride reacts with potassium thiocyanate forming red colored iron thiocyanate Fe(SCN)3.
Iron (III) chloride reacts with potassium ferrocyanide forming a deep blue precipitate of prussian blue Fe4[Fe(CN)6]3.