CHAPTER VI TTHE COMPOUNDS OF NITROGEN WITH HYDROGEN AND OXYGEN

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 oxide, and from the second H(NH 4 ) 2 NO4 - 4H 2 O = HN 3 —hydronitrous acid, and from the third (NH 4 ) 3 NO - 4H 2 O = N 4 H 4 —the ammonium salt of the same acid. The composition of HN 3 should be thus understood, whilst its acid properties are explained by the fact that the water (4H 2 O) from H(NH 4 ) 2 N_O 4 is formed at the expense of the hydrogen of the ammonium and oxygen of the nitric acid, so that there remains the same hydrogen as in nitric acid, or that which may be replaced by metals and give salts. Moreover, nitrogen undoubtedly belongs to that category of metalloids which give acids, like chlorine and carbon, and therefore, under the influence of three of its atoms, one atom of hydrogen acquires those properties which it has in acids, just as in HCN (hydrocyanic acid) the hydrogen has received these properties under the influence of the carbon and nitrogen (and HN 3 may be regarded as HCN where C has been replaced by N 2 ). Moreover, besides explaining the composition and acid properties of HN 3 , the above method gives the possibility of foretelling the closeness of the bond between hydronitrous acid and nitrous oxide, for N 2 O + NH 3 = HN 3 + H 2 O. This reaction, which was foreseen from the above considerations, was accomplished by Wislicenus (1892) by the synthesis of the sodium salt, by taking the amide of sodium, NH 2 Na (obtained by heating Na in a current of NH 3 ), and acting upon it (when heated) with nitrous oxide, N 2 O, when 2NH 2 Na + N 2 O = NaN 3 + NaHO + NH 3 . The resultant salt, NaN 3 , gives hydronitrous acid when acted upon by sulphuric acid, NaN 3 + H 2 SO 4 = NaHSO 4 +HN 3 . The latter gives, with the corresponding solutions of their salts, the insoluble (and easily explosive) salts of silver, AgN 3 (insoluble, like AgCl or AgCN), and lead, Pb(N 3 ) 2 .