In _vacuo_, it expands into vapour, which still possesses the power of exploding by heat. In water, it gradually disappears, the water becoming acid, and azote being evolved. Mercury decomposes it, and a white powder (calomel) is formed, while the azote is set at liberty. Dr. Ure (_Chemical Dictionary_, Art. _Nitrogen_,) observes, that the mechanical force of this compound, seems superior to that of any other known substance, not even excepting the ammoniacal fulminating silver. The velocity of its action appears to be likewise greater. The Doctor touched a minute globule of it, in a platina spoon, resting on a table, with a fragment of phosphorus at the point of a pen-knife, and the blade was instantly shivered into fragments by the explosion. Messrs. Porret, Wilson, and Kirk (_Nicholson's Journal_, Vol. XXXIV,) employed 125 different substances, by bringing them in contact; and out of that number the following caused it to explode: Supersulphuretted hydrogen, Phosphorus, Phosphuret of lime, Phosphuretted camphor, Camphoretted oil, Phosphuretted hydrogen gas, Caoutchouc, Myrrh, Palm oil, Ambergris, Whale oil, Linseed oil, Aqueous ammonia, Olive oil, Sulphuretted oil, Oil of Turpentine, ---- Tar, ---- Amber, ---- Petroleum, ---- Orange peel, Naphtha, Soap of silver, ---- Mercury, ---- Copper, ---- Lead, ---- Manganese, Fused Potassa, Nitrous gas. See _Detonating Works_. According to Mr. Davy, chloride of azote contains 4 vols. of chlorine = 10 + } or { 4 primes = 18.0 + 1 ---- azote = 0.9722 } { 1 ---- = 1.75, or very nearly 10 by weight of chlorine to 1 of azote. _Sect. XXXII. Of Pyrophorus._ Pyrophorus is a black substance, which takes fire spontaneously, when brought into contact with air. It is the luft-zunder, or air-tinder of the Germans. It first emits sulphuretted hydrogen gas, and in a few seconds becomes red-hot, burning with a bluish flame. Pyrophorus consists of alumina, charcoal, and sulphuret of potassa, and also, according to some, of potassium, which is alleged to be formed in its preparation. Be this as it may, it seems, that water is decomposed in its combustion, that sulphuretted hydrogen gas is emitted, which is inflamed by the oxygen gas of the atmosphere, and that, during the combination of oxygen, a degree of heat is produced, which causes the ignition of the charcoal, as well as the inflammation of the remaining sulphur.