Tutton's salt

Tutton's salts are a family of salts with the formula M₂M'(SO₄)₂^.(H₂O)₆(sulfates) or M₂M'(SeO₄)₂^.(H₂O)₆ (selenates). These materials are "double salts," which means that they contain two different cations, M⁺ and M'²⁺. Some examples of Tutton salts are, M = NH₄⁺ and M' = V²⁺ and Cu²⁺. [Greenwood&Earnshaw]
They are sometimes called Schonites after the naturally occurring mineral Schönite (K₂MgSO₄.6H₂O). They are named for A.E H Tutton who identified and characterised a large range of these salts around 1900. [cite journal
title = A Comparative Crystallographical Study of the Double Selenates of the Series R₂M(SeO₄)₂.6H2O.--Salts in Which M Is Zinc.
author = A. E. Tutton
journal =Proceedings of the Royal Society of London
volume = 67
year = 1900-1901
pages =58–84
url = http://gallica.bnf.fr/ark:/12148/bpt6k56160k/f65.table
doi = 10.1098/rspl.1900.0002]
Related to the Tutton's salts are the alums, which are also double salts but with the formula MM'(SO₄)₂^.(H₂O)₁₂. The Tutton's salts were once termed "false alums" [ F.Sherwood Taylor (1942) Inorganic and Theoretical Chemistry 6th Edition, William Heinemann] . Such salts were of historical importance because they were obtainable in high purity and served as reliable reagents and spectroscopic standards.

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