Ammonium oxalate, chemical formula (NH4)2C2O4·H2O. The molecular weight is 142.11. Colorless columnar or white granular crystals. Poisonous! Exact melting point, relative density of 1.50 and refractive index of 1.546. Soluble in water, slightly soluble in alcohol, insoluble in ammonia water. Heat to 95℃ for dehydration, and decompose carbon monoxide, carbon dioxide and ammonia at high temperature. It can react with other metal salts to form oxalate with low solubility. If soluble calcium salt is added to its aqueous solution, white precipitate can be formed, and it can also be used as a ligand to form oxalic acid complexes with transition metal salts. Preparation method: Oxalic acid reacts with ammonia water (or ammonium carbonate) and is crystallized. Uses: Ammonium oxalate can be used to prepare iron-containing tin-removing dyes, organic synthetic raw materials, and as a reagent for determining calcium, lead and rare earth metal ions and a metal polishing agent.