FULMINIC ACID, a volatile explosive liquid, C : NOH, hav ing an odour of prussic acid, has not been obtained in a state of purity. It is set free from sodium or potassium fulminate by dilute sulphuric acid followed by extraction with ether. The chemical constitution of fulminic acid and its salts has long been a matter of controversy among chemists, although the general consensus of opinion favours the view epitomized by the forego ing chemical formula which represents the acid as carbyloxime (carbonyloxime) or the oxime (q.v.) of carbon monoxide. Ac cordingly fulminic acid belongs to the small group of organic substances regarded as containing bivalent carbon. The best known fulminates are those of mercury and silver. The prepara tion of the former is described under MERCURY, FULMINATE oF; the latter is produced similarly by adding ethyl alcohol to a nitric acid solution of silver nitrate. The liquid is gently heated until frothing occurs and when the vigorous reaction has subsided, silver fulminate, C : NOAg, separates in opaque white needles which are sparingly soluble in water. This salt is an extremely dangerous compound since it detonates even more violently than the mercury compound. Cadmium, cuprous and thallous fulminates have been prepared (L. Wohler and Martin, 1917) ; they are all violently explosive.
The production of fulminate from ethyl alcohol, acetaldehyde and similar two-carbon compounds supported the older view that fulminic acid and its salts also contained two carbon atoms in the molecule but this hypothesis was disproved com pletely by J. U. Nef (1894) who prepared fulminates from or ganic compounds containing only one carbon atom. For example, he obtained mercuric fulminate by the interaction of mercuric chloride and sodium nitromethane, : NO.ONa. Another neat synthesis of metallic fulminates from a one-carbon compound was discovered by H. Wieland (1907) : on warming methylnitrolic acid, with excess of silver nitrate in dilute nitric acid silver fulminate separates in considerable yield. The syn thesis of benzaldoxime from benzene and mercuric fulminate in presence of hydrated aluminium chloride (R. Scholl, 1899) is corroborative evidence in favour of the carbyloxime structure of fulminic acid. Further confirmation is afforded by the physico chemical evidence adduced by L. Waller (19o5) who, by the freezing-point method, found that in decinormal aqueous solu tion, sodium fulminate had an apparent molecular weight of 34.9 this corresponds with the molecular weight of undissociated C : NONa, divided by the dissociation factor (1.85) generally observed for sodium salts of monobasic acids. This result ex cludes the dimeric formula, Fulminuric Acid, colourless prisms soluble in water and deflagrating at 145°C, is obtained through its ammonium salt by boiling mer curic fulminate with an aqueous solution of ammonium chloride. Meta f ulminic Acid, containing water and melting at 85-86° C, and at 102° C when anhydrous, is formed by the spon taneous polymerization of fulminic acid.
See "Fulminic and Fulminuric Acids," Thorpe's Dictionary of Applied Chemistry, vol. iii., p. 28o (5922). (G. T. M.)