Howard's fulminating mercury is less dangerous than either fulminating silver, or fulminating gold. The extreme force of detonation which it possesses is remarkable. The temperature required for its explosion is 360 degrees. Friction, percussion, electricity, and the flint and steel will produce this effect. It gives rise to a stunning disagreeable report, and its force is sufficient to indent both the hammer and the anvil. Four or six grains are sufficient for an experiment. It is rather singular, as Mr. Cruikshank first observed, that this powder will not inflame gunpowder; as may be shown by spreading some of the former on paper, and shaking gunpowder over it, and then firing the mercurial powder. The grains of the gunpowder may be collected entire after the explosion.
From the experiments of Howard, it appears, that this powder is composed of oxalate of mercury, and nitrous etherised gas. Fourcroy, however, has shown, that it varies in its nature, according to the mode of its preparation.
There is also a preparation of mercury, which is likewise explosive, discovered by Fourcroy. This compound may be formed by digesting the red oxide of mercury in liquid ammonia for the space of eight or ten days. The oxide assumes a white colour, and at last appears in crystalline scales. Upon ignited coals, it detonates loudly like fulminating gold, which see below. In a few days, however, it loses its fulminating property, and undergoes spontaneous decomposition. Exposed to a low heat, the ammonia is disengaged, and an oxide of mercury remains.
As ammonia forms several detonating compounds with metallic oxides, the theory of their explosive effects is the same; viz. that, while the hydrogen of the ammonia unites with the oxygen of the oxide, forming water, the azote is disengaged in the state of gas.
The process for preparing Howard's fulminating mercury is the following, dissolve one hundred grains of mercury in an ounce and a half (by measure) of common nitric acid, assisting the solution by heat. When cold, pour the solution upon two ounces (by measure) of strong alcohol, and apply a moderate heat, until the mixture begins to effervesce. A white fume then begins to undulate on the surface of the liquor, and a white powder precipitates, which is the fulminating mercury. This powder is to be immediately washed with cold water, and dried at a heat, not much exceeding that of boiling water. One hundred grains of mercury, will give, on an average, one hundred and twenty-five grains of the powder.
The products of its combustion are carbonic acid gas, azotic gas, water, and mercury. Besides by percussion, it is inflammable when brought in contact with sulphuric acid. It is supposed, that fulminating mercury sometimes contains ammonia, and that the products of combustion, according to the mode of preparation, are therefore different. The reader may consult some interesting observations on this powder in the Journal de l'Ecole Polytechnique.
M. Bayen, an apothecary, in 1779, (Journal de Physique), announced a process for preparing fulminating mercury. His process, however, is different from that described. A solution of mercury is made in nitric acid, and precipitated by caustic alkali. The precipitate (oxide of mercury) is then caught on a filter, washed, and dried. Thirty grains of this powder, mixed with four or five grains of sulphur, and struck with a heavy hammer, or heated on an iron, will explode with violence. The oxide of mercury, obtained from its solution by lime-water, has the same effect, when treated in the same manner. Another process recommended is, to precipitate a solution of the perchloride of mercury (corrosive sublimate) by lime-water, and treat the precipitate with sulphur, as above described.
Sect. XXVI. Of Fulminating Silver.
This compound, which is more powerful than fulminating mercury, is prepared also with alcohol. Descostils (Annales de Chimie, LXII. p. 198,) Cruikshank, and Brugnatelli, have all written upon it.
Fulminating silver explodes without much heat. By the slightest friction it is inflamed, and detonation follows. Hence it is used in the form of toys, in fulminating balls, bombs, crackers, &c. which explode by falling on the ground. Torpedoes, pulling crackers, &c. are formed of this powder. The fulminating balls are made of glass, and contain a grain or two of fulminating silver, mixed with sand. The same mixture, put on the ends of two strips of paper, and the ends pasted, forms the pulling crackers; for the moment they are pulled asunder, the friction produced sets the fulminating silver on fire, and causes a detonation.