Isododecylphosphetanic and diisooctylphosphinic acids can also be used for this function. The kerosene mixture is then backwashed with an acid to recover the metals in a water solution and regenerate the extracting fluid. Production Indium metal reacts with cold concentrated sulfuric acid to produce Indium sulfate and hydrogen gas. If hot concentrated sulfuric acid is used indium will reduce the sulfuric acid to sulfur dioxide. Indium sulfate can also be produced from a reaction of sulfuric acid on indium oxide, indium carbonate, or indium hydroxide. Reactions When heated to or above, indium sulfate decomposes by giving off sulfur trioxide vapour, yielding indium oxide. In2(SO4)3 -> In2O3 + 3SO3 Alkalis added to indium sulfate solutions precipitate basic salts. For example, potassium hydroxide produces either a basic sulfate, 2In2O3.SO3·nH2O, or KIn3(OH)6(SO4)2 depending on pH. Sodium pyrophosphate causes a slimy precipitate of indium pyrophosphate, In4(P2O7)3·3H2O. Potassium periodate causes a precipitate of a basic indium periodate, 2InO5·In(OH)3·6H2O . Oxalic acid causes a precipitate of indium oxalate, In2(C2O4)3·10H2O. Alkali oxalates cause a precipitate of the alkali dioxalatoindate to form MIn(C2O4)2·3H2O, where M = Na, K or NH4. Related compounds Hydrogen sulfates An acid sulfate, indium hydrogensulfate tetrahydrate with the formula HIn(SO4)2·4H2O crystallises in the orthorhombic system with unit cell dimensions a = 9.997 Å, b = 5.477 Å, c = 18.44 Å, with four of the formula per cell. The density is 2.50 cm−3. In the acid sulfate, two water molecules are linked to the indium atom and a hydronium ion H5O2 takes care of the proton. This is part of an acid sulfate family that includes Al, Ga, In, Tl(III), Fe(III) and Ti(III). HIn(SO4)2 is made by evaporating an indium sulfate in 40% sulfuric acid solution or cooling indium sulfate in a 60% sulfuric acid solution. 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. Indium hydrogensulfate is a proton conductor with conductivity 0.0002Ω−1cm−1. Basic sulfates A basic indium sulfate is made by adding ethanol to a water solution of indium sulfate. Crystals can be formed by using a 0.05 molar solution with twice the volume of ethanol, and waiting for several weeks for crystals to form. InOHSO4·(H2O)2 has monoclinic crystals with a=6.06 Å b=7.89 Å c=12.66 Å and β=107.5°. Cell volume is 577.6 Å3.