The oxides and hydroxides of complex groups show analogy in their formulas, and often in their methods of preparation with the basic oxides and hydroxides. A few instances of these will now be given.

Ammonia (see p. 42) is very soluble in water ; at the ordinary temperature, no less than 800 volumes of the gas dissolve in one volume of water, forming a very pungently smelling solution named liquor ammonia. The solution consists for the most part of a mixture of liquid ammonia with water; it probably also contains ammonium hydroxide, NH4OH, and, as already mentioned, less than 1.5 per cent, of the ions NH4and -OH. It is, therefore, a weak base.

Hydrazine, N2H4, also forms a hydrate, N2H5OH, a fuming liquid with slight smell (and consequently in all probability fairly highly ionised) ; it boils at 1190, and is very corrosive, attacking wood, cork, and even glass. It has a strong reducing action, so that if added to a solution of cupric sulphate which contains cupric ions, Cu, it gives an immediate precipitate of cuprous oxide, Cu2O, nitrogen being evolved. Like ammonia, it precipitates such hydroxides as that of aluminium, iron, etc. Hydroxylamine, NH2OH, is a somewhat similar body, produced by passing nitric oxide, NO (see p. 97), through a mixture of granulated tin and hydrochloric acid, to which a little platinic chloride has been added ; the nascent hydrogen reduces the nitric oxide to hydroxylamine ; it unites with the hydrochloric acid, forming hydroxylamine hydrochloride, NH3OHCI. After removal of the tin by addition of sodium hydroxide and filtration, the solution is evaporated to dryness and mixed with alcohol; hydroxylamine hydrochloride dissolves, while sodium chloride remains. A solution of the base may be obtained by addition of silver hydroxide : NH3OHCI.Aq + AgOH.Aq = AgCl + NH3OH.Aq. If sodium methoxide (see p. 88) be added to a solution of the hydrochloride in methyl alcohol, the base is liberated, and can be separated from the alcohol by fractional distillation ; it is a volatile white solid. This compound is interesting, because its OH group is under no circumstances an ion; its solution in water must contain ions of NH3OH and -OH, since it reacts like ammonium hydroxide.