Oxalic acid
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. 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.