HCN is hydrogen cyanide, also known as cyanide. In the standard state, it is gas, highly toxic and deadly, colorless and bitter, with almond flavor. Whether it can be sniffed depends on individual genes. Hydrogen cyanide is a colorless toxic liquid with a boiling point of 26℃ (79 F), which is slightly higher than room temperature.

First, potassium ferricyanide is decomposed into iron carbide, sodium cyanide (potassium cyanide) and nitrogen. Nitrogen escapes directly. Only the reacted solid remains. Dissolve the solid with water until only insoluble matter remains, and then filter out the black solid iron carbide. Finally, hydrochloric acid is added into the solution for reaction to obtain hydrogen cyanide.