The same preparation placed on a wafer, and the wafer put between paper, as in the sealing of a letter, will explode, when the paper or the wafer is broken. Fulminating bombs are balls of the size of a hazle nut, containing about three grains of the fulminating silver. Their explosive effects are said to be violent. See [Detonating Works.]
This powder, in consequence of its powerful action, is dangerous; and, as it explodes so readily, it should never be put into a phial, nor should it be touched or handled in any way that can produce friction. Even when made to approach the flame of a candle, it will explode with extreme violence.
The preparation of Brugnatelli's fulminating silver consists in reducing 100 grains of nitrate of silver (lunar caustic) to powder; and, when put into a basin, pouring over it one ounce of alcohol, and the same quantity of nitric acid. The mixture will become hot, effervescence will ensue, while the whole will assume an opaque or milky appearance.
When the gray powder of the nitrate has become white, and the mixture acquires consistency, distilled water is to be added, to suspend the action. The white precipitate is then to be washed by repeated affusions of cold water, and dried in the open air, but in a dark place, so as to seclude it from the light.
In fact, this process is similar to that for preparing fulminating mercury; for it is nothing more than treating silver with nitric acid and alcohol. Cruikshank employs forty parts of silver, sixty parts of nitric acid, and sixty parts of alcohol, from which sixty parts of the powder are obtained.
Berthollet considers this powder to be composed of ammonia, and oxide of silver, and the theory of its detonation to be the same as that of fulminating gold. In its explosion, the oxygen of the oxide of silver unites with the hydrogen of the ammonia, and the nitrogen is disengaged.
Berthollet's fulminating silver, which he discovered in 1788, is another preparation, which fulminates powerfully. It is prepared by precipitating nitrate of silver by lime-water. The precipitate is placed on filtering paper, which absorbs the water, and the nitrate of lime. Pure caustic ammonia is then added, which produces an effect somewhat similar to that attending the slaking of lime. The ammonia dissolves only a part of this precipitate. It is left at rest for ten or twelve hours, and at the expiration of this time, there is formed, on the surface, a shining pellicle, which is re-dissolved with a new portion of ammonia, but which does not appear, if a sufficient quantity of ammonia has been added at the first. The liquid is then separated, and the black precipitate, found at the bottom, is put, in small quantities, on separate papers. This powder explodes even when moist, if struck with a hard body. When dry, the slightest friction will explode it. Its detonation is owing to the same cause as that producing the explosion of the other preparation of this metal, as it is also composed of oxide of silver and ammonia.
The fulminating silver of Chenevix explodes only by a slight friction in contact with combustible substances. It is nothing more than chlorate of silver. It is formed by passing chlorine gas through alumina, diffused in water, and afterwards digesting, in the liquor, some phosphate of silver. The whole is to be evaporated slowly. A single grain of this powder, with three grains of sulphur, will explode by the slightest friction.
For the preparation of fulminating silver, the formula given by professor Silliman of Yale College, appears to possess some advantages. To an ounce of alcohol and as much nitric acid, he adds 100 grains of pulverized lunar caustic. A gentle heat is applied to excite the action between them, which must be removed, the moment they begin to act. When a thick white precipitate appears, cold water must be added to check the action. The precipitate is then to be collected, washed, and carefully dried. A grain or two will explode over a candle.
Sect. XXVII. Of Fulminating Gold.