The essential difference between an explosion and a detonation is the comparative suddenness of the transformation of the solid or liquid explosive substance into gas and vapour.
Some explosive bodies, such as the fulminates, &c., always detonate, while the detonation of others depends on the mode of firing.
Nitro-glycerine always explodes violently, but when fired with an initiatory charge of fulminate of mercury it is much more powerful than when fired with gunpowder.
Compressed gun-cotton in the air-dry state can be detonated by 2 grains of fulminate of mercury embedded in the material, but when it contains 3 per cent. of water over and above the 2 per cent. which exists normally in the air-dry substance, 15 grains of the fulminate will not always do so.
Theory of Detonation.—The theory of detonation is not yet thoroughly understood. That it is not alone due to the heat caused by the impact of the mechanical energy of the particles of gas, set free from the initiatory charge on the principal mass, is proved by the fact of its being possible to detonate wet gun-cotton.
Professor Bloxam terms detonation to be "sympathetic" explosion.
Experiments carried on in England by Professor Abel, and in France by MM. Champion and Pellet, tend to show that it is due to the vibratory action of the detonating agent.
Thus a glass may withstand a strong blow, though a particular note or vibration will smash it.
All explosive compounds and mixtures, including gunpowder, are susceptible of violent explosion through the agency of a detonation.
Roux and Sarrau.—Roux and Sarrau divide explosions into two orders:—