nitrogen, carbonic anhydride, CO 2 , carbonic oxide, CO, and aqueous vapour. In the explosion of nitro compounds much heat is evolved, as in the combustion of gunpowder or detonating gas, and in this case the force of explosion in a closed space is great, because from a solid or liquid nitro-compound occupying a small space there proceed vapours and gases whose elasticity is great not only from the small space in which they are formed, but owing to the high temperature corresponding to the combustion of the nitro-compound.
If the vapour of nitric acid is passed through an even moderately heated glass tube, the formation of dark-brown fumes of the lower oxides of nitrogen and the separation of free oxygen may be observed, 2NHO 3 = H 2 O + 2NO 2 + O. The decomposition is complete at a white heat—that is, nitrogen is formed, 2NHO 3 = H 2 O + N 2 + O 5 . Hence it is easily understood that nitric acid may part with its oxygen to a number of substances capable of being oxidised. It is consequently an oxidising agent . Charcoal, as we have already seen, burns in nitric acid; phosphorus, sulphur, iodine, and the majority of metals also decompose nitric acid, some on heating and others even at the ordinary temperature: the substances taken are oxidised and the nitric acid is deoxidised, yielding compounds containing less oxygen. Only a few metals, such as gold and platinum, do not act on nitric acid, but the majority decompose it; in so doing, an oxide of the metal is formed, which, if it has the character of a base, acts on the remaining nitric acid; hence, with the majority of metals the result of the reaction is usually not an oxide of the metal, but the corresponding salt of nitric acid, and, at the same time, one of the lower oxides of nitrogen. The resulting salts of the metals are soluble, and hence it is said that nitric acid dissolves nearly all metals. This case is termed the solution of metals by acids, although it is not a case of simple solution, but a complex