Silver fulminate

Silver fulminate (AgCNO) is the highly explosive silver salt of fulminic acid.

Silver fulminate is a primary explosive that has very little practical value 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. Aggregation of 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. Since its discovery, its only practical usage has been in producing non-damaging novelty noisemakers as children's toys and tricks.

Structure

Silver fulminate occurs in two polymorphic forms, an orthorhombic one and a trigonal one with a rhombohedral lattice. The trigonal polymorph consists of cyclic hexamers, (AgCNO)₆.

Preparation

This compound can be prepared by the reaction of concentrated nitric acid with silver metal and ethanol, under careful control of the reaction conditions, to avoid explosion. Only very tiny amounts of silver fulminate should be prepared at once, as even the weight of the crystals can cause them to self-detonate.

Silver fulminate can be prepared unintentionally, when an acidic solution of silver nitrate comes in contact with alcohol. This is a hazard in the chemical silvering of mirrors.

Novelty explosive

Silver fulminate, often in combination with potassium chlorate, is used in trick noise-makers known as "crackers", "snappers", "whippersnappers", "pop-its", or "bang-snaps", a popular type of novelty firework. They contain approximately 200 milligrams of fine gravel impregnated with a minute quantity (approximately 80 micrograms) of silver fulminate. When thrown against a hard surface, the impact is sufficient to detonate the tiny quantity of explosive, creating a small report 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. 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.