Prep. Made by first neutralizing a solution of one ounce of purified oxalic acid in eight ounces of boiling distilled water, with carbonate of ammonia; filtering the solution, cooling, and allowing the oxalate of ammonia to crystallize. The crystals have the composition (Nh4 O, C2 O3 + HO). Of these crystals, dried on filtering paper by simple exposure to air, and free from efflorescence, half an ounce is dissolved in one pint of distilled water.

Use. The solution of oxalate of ammonia is used for detecting the presence of lime in solution. It forms, in very dilute neutral or alkaline solutions of the salts of lime, a precipitate of oxalate of lime, which is insoluble in acetic acid, but soluble in nitric and hydrochloric acids. It is applied for this purpose to test many of the Pharmacopoeia substances - tartaric and citric acids, liquor ammonias fortior, creta preparata, calcis phosphas, calx, carbonate and citrate of lithia, sulphate of magnesia, and many other substances in the Materia Medica.