Ammonia gas is absorbed in concentrated brine to give a solution containing both sodium chloride and ammonia. Na+(aq), Cl-(aq), NH4+(aq), OH-(aq) ions and NH3(aq) are present.
The 4th and 5th sections describe some important uses of ammonia and nitric acid, including the use of ammonium and nitrate salts as artificial fertilisers and problems with their use.
The last two stages, (6) and (7), are concerned with the regeneration of ammonia from ammonium chloride (made in step 3). The quicklime from step (2) is slaked with excess water giving milk of lime: