Tuttons

Tutton's salts are a class of double sulfate salts consisting of ammonium and a divalent metal cation. The general formula is (NH4)2[M(SO4)2]·6H2O, where M2+ is a divalent metal such as Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, or Mg2+. These salts crystallize from aqueous solution as hexahydrates and often show isomorphism across different metals.

The physical properties of Tutton's salts depend on the metal ion. The crystals are typically color influenced by the specific metal, for example Cu2+ salts are blue, Ni2+ salts are green to blue-green, Mn2+ salts are pale pink, Co2+ salts are pink to red, Fe2+ salts can be greenish, and Zn2+ or Mg2+ salts are often colorless. They are stable in water under ordinary conditions and may decompose upon heating, releasing water and forming anhydrous sulfate species.

Preparation usually involves crystallization from an aqueous solution containing both ammonium sulfate and a soluble metal sulfate in appropriate proportions. The resulting hexahydrate salts are used in inorganic chemistry demonstrations and qualitative analysis to illustrate concepts of double salts, hydration, and crystal structure.

History and nomenclature reflect the work of a 19th–early 20th century chemist after whom the compounds are named. Tutton's salts remain a classic example of isomorphous, hydrated double salts in inorganic chemistry.