indium sulfate solution with extra sulfuric acid added. Indium ammonium alum NH4In(SO4)2·12H2O is fairly unstable at room temperature and must be crystallised below 5 °C. It decomposes at 36 °C to a tetrahydrate. It changes to a ferroelectric phase below 127K. The alum methyl ammonium indium sulfate dodecahydrate CH3NH3In(SO4)2·12H2O becomes ferroelectric below 164K. Potassium indium alum has not been crystallised. Rubidum indium alum is highly efflorescent very easily losing its water. Another series of monoclinic hydrated double salts have four water molecules MIn(SO4)2·4H2O, with five formulae per unit cell, where M is NH4, K or Rb and the point group is P21/c. The prototype substance for the series is (NH4)Sm(SO4)2(H2O)4. Cadmium can also form a double sulfate, Cd3In2(SO4)6·26H2O. Crystals with less water also exist like KIn(SO4)2·H2O. Organic double sulfates Organic base double sulfates of indium include the guanidinium salt [C(NH2)3][In(H2O)2(SO4)2], which crystallises in a monoclinic system with space group P21/c a = 4.769 Å, b = 20.416 Å, c = 10.445 Å, β = 93.39°, cell volume 1015.3 Å3, 4 formulas per cell and density 2.637. [H2(4,4'-bi-py)][In2(H2O)6(SO4)4]·2H2O crystallises in the triclinic system with a = 7.143 Å, b = 7.798 Å, c = 12.580 Å, α = 107.61°, β = 98.79°, γ = 93.89°, cell volume 655.2 Å3, one formula per cell and density 2.322. [H(2,2'-bipy)][In(H2O)(SO4)2]·2H2O, the hexamethylenediamine salt [H3N(CH2)6NH3][In(H2O)2(SO4)2]2·2H2O and [H2(Py(CH2)3Py)][In(H2O)2(SO4)2]2·2H2O also exist. Yet other organic derivatives include those of triethylenetetramine, and amylammonium. Tri-μ-sulfato-κ6O:O'-bis[aqua(1,10-phenanthroline-κ2N,N')indium(III)] dihydrate, [In2(SO4)3(C12H8N2)2(H2O)2]·2H2O, has a 1,10-phenanthroline molecule linked to each indium ion. Two indium ions are linked via three sulfate groups. It forms triclinic crystals with two formulas per unit cell. The density is 2.097 g/cm3. Dimethylindium sulfate [(CH3)2In]2SO4 can be made by reacting trimethylindium with dry sulfuric acid. Mixed A double indium sulfate chloride salt has formula In2(SO4)3·InCl3·(17±1)H2O. Monovalent Indium(I) sulfate, In2SO4 can be made in a solid state by heating indium metal with indium(III) sulfate, but when dissolving in water or sulfuric acid, In+ reacts to produce hydrogen gas. The mixed valence salt InIInIII(SO4)2 is also made by heating indium metal with indium(III) sulfate. Use Indium sulfate is a commercially available chemical. It can be used to electroplate indium metal, as a hardening agent in gold electroplating or to prepare other indium containing substances such as copper indium selenide. It has been sold as a health supplement, even though there is no evidence of benefit to humans, and it is toxic. The first high-frequency