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received these properties under the influence of the carbon and nitrogen (and HN 3 may be regarded as HCN where C has been replaced by N 2 ).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 .
The compounds of nitrogen with oxygen present an excellent example of the law of multiple proportions, because they contain, for 14 parts by weight of nitrogen, 8, 16, 24, 32, and 40 parts respectively by weight of oxygen. The composition of these compounds is as follows:—
| N 2 O, nitrous oxide; hydrate NHO. |
|---|
| N 2 O 2 , nitric oxide, NO. |
| N 2 O 3 , nitrous anhydride; hydrate NHO 2 . |
| N 2 O 4 , peroxide of nitrogen, NO 2 . |
| N 2 O 5 , nitric anhydride; hydrate NHO 3 . |
Of these compounds,33 nitrous and nitric oxides, peroxide of nitrogen, and nitric acid, NHO3, are characterised as being the most stable.
The lower oxides, when coming into contact with the higher, may give the intermediate forms; for instance, NO and NO2 form N2O3, and the intermediate oxides may, in splitting up, give a higher and lower oxide.
So N2O4 gives N2O3 and N2O5, or, in the presence of water, their hydrates.
We have already seen that, under certain conditions, nitrogen combines with oxygen, and we know that ammonia may he oxidised.
In these cases various oxidation products of nitrogen are formed, but in the presence of water and an excess of oxygen they always give nitric acid. Nitric acid, as corresponding with the highest oxide, is able, in deoxidising, to give the lower oxides; it is the only nitrogen acid whose salts occur somewhat widely in nature, and it has many technical uses, for which reason we will begin with it.