Thus nitrogen gives a series of oxygen compounds, which we will proceed to describe. We will, however, first show by two examples that in the first place the passage of ammonia into the oxygen compounds of nitrogen up to nitric acid, as well as the converse preparation of ammonia (and consequently of the intermediate compounds also) from nitric acid, are reactions which proceed directly and easily under many circumstances, and in the second place that the above general principle of substitution gives the possibility of understanding many, at first sight unexpected and complex, relations and transformations, such as the preparation of hydronitrous acid, HN 3 . In nature the matter is complicated by a number of influences and circumstances, but in the law the relations are presented in their simplest aspect.
- It is easy to prove the possibility of the oxidation of ammonia into nitric acid by passing a mixture of ammonia and air over heated spongy platinum. This causes the oxidation of the ammonia, nitric acid being formed, which partially combines with the excess of ammonia.
The converse passage of nitric acid into ammonia is effected by the action of hydrogen at the moment of its evolution.31 Thus metallic aluminium, evolving hydrogen from a solution of caustic soda, is able to completely convert nitric acid added to the mixture (as a salt, because the alkali gives a salt with the nitric acid) into ammonia, NHO3 + 8H = NH3 + 3H2O.
In 1890 Curtius in Germany obtained a gaseous substance of the composition HN 3 (hydrogen trinitride), having the distinctive properties of an acid, and giving, like hydrochloric acid, salts; for example, a sodium salt, NaN 3 ; ammonium salt, NH 4 N 3 = N 4 H 4 ; barium salt, Ba(N 3 ) 2 , &c., which he therefore named hydronitrous acid, HN 3 . The extraordinary composition of the compound (ammonia, NH 3 , contains one N atom and three H atoms; in HN 3 , on the contrary, there are three N atoms and one H atom), the facile decomposition of its salts with an explosion, and above all its distinctly acid character (an aqueous solution shows a strong acid reaction to litmus), not only indicated the importance of this unexpected discovery, but at first gave rise to some perplexity as to the nature of the substance obtained, for the relations in which HN 3 stood to other simple compounds of nitrogen which had long been known was not at all evident, and the scientific spirit especially requires that there should be a distinct bond between every innovation, every fresh discovery, and that which is already firmly established and known, for upon this basis is founded that apparently paradoxical union in science of a conservative stability with an irresistible and never-ceasing improvement. This missing, connection between the newly discovered hydronitrous acid, HN 3 , and the long known ammonia, NH 3 , and nitric acid, HNO 3 , may be found in the law of substitution, starting from the well-known properties and composition of nitric acid and ammonia, as I mentioned in the ‘Journal of the Russian Physico-Chemical Society’ (1890). The essence of the matter lies in the fact that to the hydrate of ammonium, or caustic ammonia, NH 4 OH, there should correspond, according to the law of substitution, an ortho-nitric acid ( see Note ), H 3 NO 4 = NO(OH) 3 , which equals NH 4 (OH) with the substitution in it of ( a ) two atoms of hydrogen by oxygen (O—H 2 ) and ( b ) two atoms of hydrogen by the aqueous radicle (OH—H). Ordinary or meta-nitric acid is merely this ortho-nitric acid minus water. To ortho-nitric acid there should correspond the ammoniacal salts: mono-substituted, H 2 NH 4 NO 4 ; bi-substituted, H(NH 4 ) 2 NO 4 ; and tri-substituted, (NH 4 ) 3 NO 4 . These salts, containing as they do hydrogen and oxygen, like many similar ammoniacal salts (see, for instance, Chapter IX.—Cyanides), are able to part with them in the form of water. Then from the first salt we have H 2 NH 4 NO 4 - 4H 2 O = N 2 O—nitrous