Silver fulminate (AgCNO) is the highly explosive silver salt of fulminic acid.
Silver fulminate is a primary explosive, but has limited use as such due to its extreme sensitivity to impact, heat, pressure, and electricity. The compound becomes progressively sensitive as it is aggregated, even in small amounts; the touch of a falling feather, the impact of a single water droplet, or a small static discharge are all capable of explosively detonating an unconfined pile of silver fulminate no larger than a dime and no heavier than a few milligrams. Aggregating larger quantities is impossible, due to the compound's tendency to self-detonate under its own weight.
Silver fulminate was first prepared in 1800 by Edward Charles Howard in his research project to prepare a large variety of fulminates. Along with mercury fulminate, it is the only fulminate stable enough for commercial use. Detonators using silver fulminate were used to initiate picric acid in 1885, but since have been used only by the Italian Navy. It can also be recrystallized from a 20% solution of ammonium acetate. The trigonal polymorph consists of cyclic hexamers, (AgCNO)<sub>6</sub>.
Preparation
This compound can be prepared by pouring a solution of silver nitrate in nitric acid into ethanol, under careful control of the reaction conditions, to avoid an explosion.
:AgNO<sub>3</sub> + HNO<sub>3</sub> + C<sub>2</sub>H<sub>5</sub>OH → AgCNO + byproducts
The reaction is usually done at 8090 °C; at 30 °C, the precipitate may not form. of silver fulminate. When thrown against a hard surface, the impact is sufficient to detonate the tiny quantity of explosive, creating a small salute from the supersonic detonation. Snaps are designed to be incapable of producing damage (even when detonated against skin) due to the buffering effect provided by the much greater mass of the gravel medium. It is also the chemical found in Christmas crackers having first been used for that purpose by Tom Smith in 1860. The chemical is painted on one of two narrow strips of card, with abrasive on the second. When the cracker is pulled, the abrasive detonates the silver fulminate.
A fulminate mixture with 1020% potassium chlorate is cheaper and more brisant than the fulminate alone.