[8] The proportion of sulfate complex increases with temperature showing the reaction that forms it is endothermic.

[13] The Raman spectrum of the solution shows lines at 650, 1000 and 1125 cm−1 due to a sulfur–oxygen bonds in sulfate bound to indium.

The kerosene mixture is then backwashed with an acid to recover the metals in a water solution and regenerate the extracting fluid.

[17] Alkalis added to indium sulfate solutions precipitate basic salts.

For example, potassium hydroxide produces either a basic sulfate, 2In2O3 · SO3 · n H2O, or KIn3(OH)6(SO4)2 depending on pH.

In the acid sulfate, two water molecules are linked to the indium atom and a hydronium ion H5O2 takes care of the proton.

[22] As the acid tetrahydrate is heated it gives off water yielding a trihydrate, monohydrate, and an anhydrous form at 370, 385 and 482K.

Above 505K it gives out more water and sulfur dioxide yielding the neutral indium sulfate.

[24] This insoluble basic salt also forms if indium sulfate solution is diluted below 0.005 molar.

One is from the family MI3MIII(XO4)3, with MI being a large singly positive ion such as K, Rb, Cs, Tl or NH3; MIII is triply charged and can be Al, Ga, In, Tl, V, Cr, Fe, Sc and other rare earths; and X is S or Se.

However, when it is heated enough, dynamical disorder causing random orientations makes the ions on average spherically symmetric.

Alkali metal ions are spherical in shape at all temperatures and form rhombohedral structures.

[25] Double sulfates of this form exist of indium with the alkali metals sodium, potassium, rubidium, and cesium.

These can be made by heating a mixture of anhydrous sulfates at 350 °C, or by dehydrating hydrous double alum type salts at 300 °C.

[26] Hydrated double salts of indium in an alum structure exist with formula MIIn(SO4)2 · 12 H2O.

[35] Rubidum indium alum is highly efflorescent very easily losing its water.

[36] Another series of monoclinic hydrated double salts have four water molecules MIn(SO4)2 · 4 H2O, with five formulae per unit cell, where M is NH4, K or Rb and the point group is P21/c.

[44] Dimethylindium sulfate [(CH3)2In]2SO4 can be made by reacting trimethylindium with dry sulfuric acid.

[53] These were made by etching depressions into an N-type germanium base from both sides with jets of indium sulfate until it was a few ten-thousandths of an inch thick.