Fulminate of Mercury

MERCURY, FULMINATE OF. A highly explosive corn pound used in percussion caps and detonators. Substances which fulminate on heating or gentle percussion have been known for a long time, but the first of which we have any definite chemical knowledge was mercury fulminate, a substance first made by E. C. Howard in 1799. J. von Liebig, who is stated to have become acquainted with the substance when he was a boy, succeeded in isolating fulminic acid whilst working in Gay Lussac's laboratory in 1823. Previous attempts appear to have been made to utilize the explosive property of fulminate for igniting gunpowder and led to many inventions.

Mercury fulminate is retained for two military purposes : as an igniter in so-called cap-compositions; and (2) as a detonator, in which case it may be used alone or mixed with a nitro-deriva tive, such as trinitrotoluene, where it can act as "starter" of a more powerful detonator.

Being too rapid in action, pure mercury fulminate will not ignite gunpowder, the grains being merely scattered. The application of fulminate as a for setting fire to gunpowder, while being itself fired by percussion, has been reached by methods of "taming" or slowing down the detonating action by addition of diluents. These diluents, which could be ignited by the fulminate, burned at a sufficiently slow rate to set fire to the gunpowder or other propellant. The slowing down or taming mixture consists, generally, of sulphide of antimony, and potassium chlorate, both in very fine powder, the fulminate being used in small crystals as made, for it cannot be ground or powdered. A silver fulminate was made by L. G. Brougnatelli in 1798, who dissolved silver in nitric acid and added this solution to spirits of wine. The white powder obtained is extremely sensitive to fric tion, percussion or heat and apparently unsuited to any practical application. Other fulminating substances obtained before this

date by the action of ammonia on solutions of gold or silver are similarly unsuitable.

Manufacture.

Clean mercury, one part, and nitric acid of sp.gr. 1.36, about ten parts, are placed in a glass flask and, after the mercury has dissolved, allowed to cool to about 15° to 20° C. Ten to twelve parts of 9o% alcohol are placed in a capacious flask and the mercury solution is added. A reaction commences in a few minutes with formation of copious white fumes followed after a short time by red gases. The action may require regulating by outward application of cold water, but generally after the tem perature has risen to 80°-90° C it settles down quietly. The reac tion mixture is poured into cold water; the sparingly soluble mer cury salt is precipitated, and is washed with cold water until free from acid. Mercury fulminate is a grey, sandy, crystalline powder, is extremely poisonous, and has a sp.gr. of about 4.4, varying a little with the conditions of formation.

Many chemists, since Liebig, have suggested constitutional formulae for fulminic acid (q.v.); it may not be quite settled even now, but the formula is almost certainly correct for mercury fulminate. Since the discovery of hydrazoic acid, some of its salts, such as the azides of lead or silver, have for special purposes become rivals of fulminate (see LEAD AzinE).

BIBLIOGRAPHY.-The

Rise and Progress of the British Explosives Industry (International Congress of Applied Chemistry, 19o9) ; 0. Guttmann, The Manufacture of Explosives, Twenty Years' Progress (1909) . (W. R. Ho.)