 Mercury(II) cyanate, though its empirical formula is identical, has a different atomic arrangement; the cyanate and fulminate anions are isomers.First used as a priming composition in small copper caps beginning in the 1820s, mercury fulminate quickly replaced flints as a means to ignite black powder charges in muzzle-loading firearms.Later, during the late 19th century and most of the 20th century, mercury fulminate or potassium chlorate became widely used in primers for self-contained rifle and pistol ammunition.