Explosives that are to be used for practical purposes, however, cannot depend on the air for their supply of oxygen. It must be provided in concentrated form so as to be available even when the explosive is excluded from contact with the air. In most explosives, however, each molecule of the compound contains all the oxygen needed. Liquid oxygen itself can be used as an explosive. A porous cartridge of wood pulp, powdered aluminum, or other combustible material is soaked in liquid oxygen and fired with a detonator before the oxygen evaporates.
Instantaneous combustion produces terrific explosive force.
A few detonating explosives, such as nitrogen iodide, have no oxygen. They act when the compound splits, and the parts expand because of heat generated by the break. It is usually introduced through the action of nitric acid, which as a rule is mixed with sulfuric acid. Dynamite is nitroglycerin mixed with some absorbent substance to reduce danger of explosion from shock. It may never be known with certainty who invented black powder, the first explosive.