Fulminates are chemical compounds which include the fulminate ion. The fulminate ion, CNO- is a pseudohalic ion, acting like a halogen with its charge and reactivity. Due to the instability of the ion, fulminate salts are friction-sensitive explosives.
The best known is mercury fulminate, which has been used as a primary explosive in detonators. Fulminates can be formed from metals, such as silver and mercury, dissolved in nitric acid and reacted with alcohol. It is largely the presence of the weak single nitrogen-oxygen bond which leads to its instability. Nitrogen very easily forms a stable triple bond to another nitrogen atom, forming gaseous nitrogen.
Fulminating gold, silver, and platinum (Latin, fulmen, lightning flash, thunderbolt) are formed by precipitating solutions of these metals with ammonia. They are perhaps nitrides or hydrated nitrides, or perhaps they contain hydrogen as well as nitrogen and water of composition, but they contain no carbon and must not be eonfused with the fulminates which are salts of fulminic acid, HONC. They are dangerously sensitive, and are not suited to practical use.

Fulminates were discovered by Edward Charles Howard in 1800. Their use in firearms in a fulminating powder was first demonstrated by a Scottish minister, A. J. Forsyth, who was granted the patent to it in 1807. Joshua Shaw then made the transition to their use in metallic encapsulations, to form a percussion cap, but did not patent his invention until 1822.
In the 1820s, the organic chemist Justus Liebig discovered silver fulminate (Ag-CNO) and Friedrich Wšhler discovered silver cyanate (Ag-OCN). The fact that these substances have the same chemical composition led to an acrid dispute, which was not resolved until Jšns Jakob Berzelius came up with the concept of isomers.

Fulminic acid

Fulminic acid[12] is a compound with a molecular formula HCNO. This substance was discovered in 1824 by Justus von Liebig. It is an organic acid and an isomer of isocyanic acid, discovered one year later by Friedrich Woehler.
Fulminic acid and its salts (fulminates), for instance mercury fulminate, are very dangerous, and are often used as detonators for other explosive materials, and are examples of primary explosives. The vapors also are toxic.

IUPAC NAME: Oxidoazaniumylidynemethane

Fulminic acid was discovered by the English chemist Edward Howard, who first prepared and investigared the compound in the form of its mercury and silver salt in 1800. The discovery was the outcome of experiments that were in fact targeted at the synthesis of "muriatic" (hydrochloric)acid, which, according to prevailing ideas, was regarded as a combination of the hypothetical element "muriurn" with hydrogen and oxygen. This led Howard to attempt to combine both hydrogen and oxygen simultaneously with a suitable metal substrate, with the object of obtaining the corresponding metal "muriate". His use of mercury oxide as the "base" and of nitric acid and alcohol as the sources of oxygen and hydrogen, respectively, could not, of course, produce the intended result, but resulted in the fortuitous discovery of the first fulminate.
The discovery of the isomerism of fulminic and cyanic acid had required no knowledge of their actual structural pattern, but with the growth of organic chemistry in the second half of the 19th century, the problem of precise molecular architecture became of paramount interest. Although the fulminic acid molecule is at first sight one of the simplest chemical entities, consisting of one atom each of hydrogen, carbon, nitrogen, and oxygen, so opaque and subtle are the chemical changes involved in its formation and reactions that the task of elucidating its structure proved unusually difficult, and its solution extended over the better part of two centuries. Not the least of the difficulties was the question of its molecular size. Believed to originate from ethanol, fulminic acid was long regarded as a two-carbon compound, C2H2N2O2, an assumption that gave rise to many false stares.

Mercury(II) fulminate

Three thousand years after its discovery, the crystal structure and molecular structure of mercury fulminate [13] are determined .The alchemists of the seventeenth century were already aware that mixtures of "spiritus vini" (ethanol) and mercury in "aqua fortis" (nitric acid) made for an explosive brew. In his book Laboratorium Chymicum, Johann Kunckel von Lšwenstern describes the vigorous reaction of mercury nitrate with alcohol to form mercury fulminate (Hg(CNO)2). In 1799, the English chemist Edward Howard isolated the compound by chance, which was produced a sensation in the nascent scientific field of chemistry.

Mercury fulminate[14] [15] is prepared by dissolving mercury in nitric acid, after which the solution is poured into 95 % ethanol. After a short time, vigorous gas evolution takes place and crystals are formed. When the reaction is complete, the crystals are filtered by suction and washed until neutral. The mercury fulminate product is obtained as small, brown to grey pyramid-shaped crystals; the color is caused by the presence of colloidal mercury.
It was first prepared by Edward Charles Howard in 1800. The crystal structure of this compound was only determined in 2007.
The reaction goes as follows:
first step involves the nitration of mercury metal with excess nitric acid:

Hg + 3 OHNO2 → HgNO3 + OHNO2 + NO2

Secondly, the mercury nitrate and excess acid are added to ethanol, forming the fulminate:

HgNO3 + HNO3 + C2H6O → Hg(ONC)2

If small amounts of copper and hydrochloric acid are added to the reaction mixture, a white product is obtained. Mercury fulminate is stored under water. It is dried at 40 ĄC shortly before use. Owing to its excellent priming power, its high brisance, and to the fact that it can easily be detonated, mercury fulminate was the initial explosive most frequently used prior to the appearance of lead azide. It was used in compressed form in the manufacture of blasting caps and percussioncaps. The material, the shells, and the caps are made of copper.

IUPAC NAME: mercury (II) oxidoazaniumylidynemethane

Mercury(II) fulminate is highly sensitive to friction and shock and sparks. It is mainly used as a trigger for other explosives in precussion caps and blasting caps It explosively decomposes to form mercury, carbon monoxide, and nitrogen . Alfred Nobel put mercury fulminate into blasting caps for detonating dynamite. This relatively safe new detonator was what allowed for the huge success of dynamite. In Germany alone, the annual production of mercury fulminate in the early 20th century reached about 100,000 Kg.
Mercury fulminate is toxic and is practically insoluble in water. When dry, it is highly sensitive to shock, impact, and friction, and is easily detonated by sparks and flames. It can be phlegmatized by the addition of oils, fats, or paraffin, and also by press-molding under very high pressure.
First used as a priming composition in small copper caps after the 1830's, mercury fulminate quickly replaced flints as a means to ignite black powder charges in muzzle loading firearms. Later mercury fulminate became widely used in primers for rifle and pistol ammunition. Today, mercury fulminate has been replaced in primers by more efficient chemical substances . Those are non-corrosive, less toxic and more stable over time: lead azide, lead styphnate and tetrazene derivates.
Mercury(II) fulminate has a crystal structure. The first investigations of this crystal structure by X-ray structure analysis date from 1931. Mercury fulminate crystals are orthorhombic and the crystal consists, as expected, of separate Hg(CNO)2 molecules. Each mercury atom is surrounded by two carbon atoms. The measured positions and bond lengths confirm a molecular structure of O-N=C-Hg-C=N-O.

Silver fulminate

Silver fulminate (AgCNO) is an explosive ionic compound of silver and the fulminate anion.
Silver fulminate is a primary explosive that has very little practical value due to its extreme sensitivity. The impact of a single water droplet has been known to detonate several milligrams of silver fulminate. Even small amounts of this explosive can cause extensive shrapnel damage, and should be treated with extreme caution.
Silver fulminate was first prepared in 1800 by Edward Charles Howard in his research project to prepare a large variety of fulminates. For two hundred years it has been only useful as a curiosity explosive in toys and tricks.

Silver fulminate is prepared by the reaction employed in the preparation of Mercury Fulminate, by reacting a solution of silver in nitric acid with alcohol. Like mercury fulminate, it is also toxic.
Silver fulminate is much more sensitive than mercury fulminate. Since its detonation development distance is very short, its initiation effect is superior to that of mercury fulminate, but the compound is too sensitive to be used commercially.

IUPAC NAME: silver oxidoazaniumylidynemethane

Fulminating silver was prepared in 1788 by Berthollet who precipitated a solution of nitrate of silver by means of lime water, dried the precipitated silver oxide, treated it with strong ammonia water which converted it into a black powder, decanted the liquid, and left the powder to dry in the open air.
An altogether different product, known as BertholletŐs detonating silver (which is not a fulminate), is obtained when a solution of freshly precipitated silver oxide in ammonia is allowed to evaporate. Its probable formula is Ag3N. It is highly sensitive and explodes even during the evaporation of the ammoniacal solution.

Fulminating silver is more sensitive to shock and friction than fulminating gold. It explodes when touched; it must not be enclosed in a bottle or transferred from pIace to pIace, but must be left in the vessel, or better upon the paper, where it was allowed to dry.
The black material which deposits in a reagent bottIe of ammoniacal silver nitrate, and sometimes collects on the rim and around the stopper, contains fuiminating silver. ExpIosions are reported to have been caused by the careiess turning of the glass stopper of a bottie containing this reagent. After a test (for aldehyde, for exampIe) has been made with ammoniacai silver nitrate solution, the Iiquid ought promptIy to be washed down the sink, and all insoIubie matter Ieft in the vesseI ought to be dissolved out with dilute nitric acid.

Silver fulminate is so sensitive and so dangerous to handle that it has not been used far practical purposes in blasting or in the military art.

Gold fulminate

Since gold is so difficult to combine with other elements, all gold compounds are fairly unstable. Some much more so than others, though: In 1659, Thomas Willis and Robert Hooke demonstrated that a powder of gold hydrazide explodes on a mere concussion, without the need for air or sparks (which were once thought to be required for any kind of ignition).
Gold hydrazide (also known as aurodiamine) is a water-soluble substance obtained by letting an ammoniacal solution react with an auric hydroxide precipitate (itself obtained from a gold solution prepared with aqua regia). Gold hydrazide has a dirty olive-green color (AuHNNH2).
Gold hydrazide is apparently only one of several explosive compounds which have been called fulminating gold (aurum fulminans). Around 1603, another kind of fulminating gold ("Goldkalck" or "Gold Calx") was described as the precipitate of gold by potassium carbonate.
Prepared by gold chloride and aqueous ammonia, the explosive precipitate is largely (ClAuNH2)2NH, but on washing with ammonia hydrolysis to the more explosive (OHAuNH2)2NH.
IUPAC NAME: gold oxidoazaniumylidynemethane

Fulminating gold is described in the writings of the pseudonymous Basil Valentine,' probably written by Johann Th˜lde (or Tholden) of Hesse and actually published by him during theyears 1602-1604. The author called it Goldkalck, and prepared it by dissolving gold in an aqua regia made by dissolving sal ammoniac in nitric acid, and then precipitating by the addition of potassium carbonate solution.
The powder was washed by decantation 8 to 12 times, drained from water, and dried in the air where no sunlight fell on it, "and not by any means over the fire, for, as soon as this powder takes up a very little heat or warmth, it kindles forthwith, and does remarkably great damage, when it explodes with such vehemence and might that no man would be able to restrain it."
The author also reported that warm distilled vinegar converted the powder into a material which was no longer explosive. The name of aumm fulminans was given tothe explosive by Beguinus who described its preparation in his Tyrocinium Chymicum, printed in 1608. Fulminating gold precipitates when a solution of pure goldchloride is treated with ammonia water. The method of preparation described by Basil Valentine succeeds because the sal ammoniaeused for the preparation of the aqua regia supplies the necessary ammonia. If gold is dissolved in an aqua regia prepared from nitric acid and common salt, and if the solution is then treated with potassium carbonate, the resulting precipitate has no explosive properties.
Fulminating gold loses its explosive properties rapidly if it is allowed to stand in contact with sulfur. Fulminating gold was early used both far war and for entertainment.