That indigo produces a detonating powder by treating it with nitric acid, is evident from experiment. As it produces a purple light, it might, perhaps, be used advantageously in small fire-works.
The process described by Dr. Thomson, (System of Chemistry, VOL. IV. p. 80, Amer. edit.) is to boil one part of indigo in four parts of nitric acid. The solution will become yellow, and a resinous matter appear upon its surface. The boiling is to be stopt, and the liquor cooled. The resinous matter is then to be separated; and the solution evaporated to the consistence of honey. This is to be re-dissolved in hot water, and filtered, and a solution of potassa added, which will throw down yellow spicular crystals, consisting of bitter principle, combined with potassa. When the resin is again treated with nitric acid, the same bitter principle is produced. The spicular crystals, when wrapped up in paper, and struck with a hammer, detonate with a purple light.
Sect. XXX. Of the Fulminating Compound, called Iodide of Azote.
Iodine is a particular substance, which has the property not only of combining with oxygen and hydrogen, forming iodic and hydriodic acid, but also with various bases constituting a class of bodies, called iodides. Its union with azote produces a singular substance, which detonates with great violence, when slightly touched or heated. It may be formed, by putting a quantity of iodine into the water of ammonia. It will be gradually converted into a brownish-black matter, which is the iodide of azote. It is formed in this process by the iodine, in the first instance, decomposing a part of the ammonia; the hydrogen of which combines with a portion of the iodine, and produces hydriodic acid, which then unites with the undecomposed part of the ammonia, and forms the hydriodate of ammonia; whilst the azote the other constituent of the ammonia, unites with another portion of the iodine, and forms the compound in question.
When exposed to the air, iodide of azote gradually flies off in vapour, without leaving any residue. The products of its detonation are iodine and azotic gas.
The iodide of azote was discovered by M. Courtois, and subsequently examined by M. Colin. Iodine, brought in contact with ammoniacal gas, a combination taking place, produces a viscid shining liquid of a brownish-black colour, which, as the saturation goes on, loses its lustre.
This liquid does not detonate, and is considered to be an iodide of ammonia; but, when it is added to water, it is decomposed, as well as the water, and we obtain two new compounds, as before observed, the hydriodate of ammonia, and iodide of azote. This iodide detonates. Hence it is evident, that hydrogen united with azote, in ammonia, prevents explosion; for the moment it is taken away, by the formation of hydriodic acid, and the azote itself combines with the iodine, a fulminating compound is formed. The elements of this powder are feebly united.
It is found, that hydriodate of ammonia has the property of dissolving a large quantity of iodine, and, if suffered to remain with the iodide of azote, of decomposing it also, and setting the azote at liberty. Water is said to have the same effect, although feebly.
Iodate of potassa, a salt composed of iodic acid and potassa, when mixed with sulphur, and struck with a hammer, will detonate, in consequence of the decomposition of the iodic acid. The iodate of potassa may be formed very readily by agitating iodine with a solution of caustic potassa. The water is decomposed, and the hydriodate of potassa is also formed, which, being very soluble, remains in solution, whilst the iodate separates, on concentrating the liquor, and suffering it to stand.
Chlorate, as well as nitrate of silver, form with sulphur fulminating powders.