Many compounds of copper, mercury, silver, gold, and the metals of the platinum group are known, which admit of representation in a similar manner. They differ, however, inasmuch as the metal must be considered to have replaced more than one atom of hydrogen in one molecule of ammonium. Thus we have :
Cu'2=NH2Cl, di-cuprosammonium chloride, a black powder produced by the action of ammonia gas on warmed cuprous chloride:
Cu- NH3C1, cuprosammonium chloride, formed by dissolving cuprous chloride in ammonia ; it is a well-known absorbent for carbon monoxide and for acetylene.
Cu"=(NH3)2Cl2, cuprammonium chloride, and cupri-diammonium sulphate, Cu"=(NH3-NH3)2SO4, the former a green substance, the latter a deep blue compound; both produced by the action of ammonia on the respective cupric salt. The formation of the latter is a well-known test for copper.
With silver there are: Argentamine, a black explosive powder, probably of the formula AgNH2, produced by adding ammonia to silver hydroxide; and numerous compounds of formulae like Ag(NH3)Cl, produced by dissolving the respective silver salts in ammonia. With gold: Auric chloride, digested with ammonia, yields " fulminating gold," an explosive black substance, which is a mixture of HN^AuCl and HN=Au-NH2.
A familiar test for mercurous mercury is to add ammonia, when the compound turns black. This is due to the formation of a mixture of metallic mercury with chloro-mercuramine, Cl-Hg-NH2, a substance also produced by adding ammonia to mercuric chloride, thus : NH3.Aq + HgCl2. Aq « Cl-Hg-NH2 + HC1. Aq. This substance has been long known under the name of " white precipitate." Here, the presence of the acidic element chlorine deprives the amido-group of basic properties. On boiling this compound with ammonium chloride, mercuram-monium chloride is produced : Cl-Hg-NH2 + NH4C1 = Hg(NH3)2Cl2.
With platinum, and the other members of that group, similar compounds are produced; but their constitution can be inferred sufficiently from what has preceded.
These compounds are derivatives of ammonia; there are few similar compounds of phosphine; one, however, is produced when phosphoretted hydrogen is passed over aluminium chloride ; its formula is PH3.3 A1C13. And arsine, passed through a solution of mercuric chloride, yields Hg2AsCl.HgCl2.