Mercury(II) fulminate

Mercury fulminate (Hg(ONC)2) is a primary explosive. It is highly sensitive to friction and shock. It is mainly used as a trigger for other explosives in percussion caps and blasting caps. Mercury(II) cyanate, though its formula is identical (HgC2N2O2), is a different compound; cyanate and fulminate are isomers.

Today mercury fulminate tends to be replaced by other primary explosives which are less toxic and more stable over time: lead azide, lead styphnate and tetrazene derivatives.

Used in percussion caps, this compound quickly replaced flints as a means to ignite a black powder charge in a firearm.

Preparation
It is prepared by dissolving mercury in nitric acid and adding ethanol to the solution. It was first prepared by Edward Charles Howard in 1800.

Silver fulminate can be prepared in a similar way, but this salt is even more unstable than mercury fulminate. It can even explode under water.