Note 425 — Chapter XII · THE COPPER AND SILVER GROUPS (Continued).—THE THEORY OF COMPLEX IONS

The naming of the complex ions, which ammonia forms with metal ions, has not yet been satisfactorily settled. English writers frequently speak of "ammonio-argentic" ion and "ammonio-argentic" nitrate. German writers speak of "Silber-ammoniak" ion (Abegg, Handb. der anorg. Chem., II, 728), which would read "silver-ammonia" ion in English terms. The terminology "silver-ammonium" ion, used in this book, is based on the idea, that all these complex ions are essentially of the same nature as the well-known ammonium-ion, NH4+, the positive charge being, almost certainly, carried by nitrogen in these complex ions, as it is in ammonium-ion. The latter is a complex ion of ammonia with hydrogen-ion. The name "ammonio-argentic" ion does not bring out this close relationship and puts the emphasis on the silver, which is probably little concerned in the reactions of the complex as such. The names "silver-ammonia" ion and "silver-ammonia" nitrate sound badly and do not emphasize the relation to ammonium, potassium, sodium and similar positive ions and their salts. The term "ammonium" is, for the reasons given, used here in a generic sense for all complex ions of ammonia with simple metal ions (such as H+, Ag+, Cu2+, Zn2+ etc.), and the number of ammonia molecules, entering into the composition of a complex ion, is not indicated in the names. A similar nomenclature has long been in vogue, and has worked well, for the complex ions of metal ions with the cyanide-ion (see below). We speak of ferrocyanide, Fe(CN)64−, argenticyanide, Ag(CN)2− and Ag2(CN)32−, etc., without indicating the number of cyanide groups, CN, in the complex, and we use the same generic ending "cyanide" as is used to designate the simple cyanide ion, e.g. to designate the ion formed from potassium cyanide, KCN ⇄ K+ + CN−.