Barium Oxalate, BaC₂O₄

Barium Oxalate, BaC₂O₄, may be obtained by precipitation of a soluble barium salt with a soluble oxalate, or by the action of oxalic acid on barium hydroxide. There are apparently three hydrates, containing 3.5, 2, and 0.5 molecules of water of crystallisation respectively. From solubility determinations it may be concluded that the first is stable below 0° C., the second between 0° and 40° C., and the third above 40° C.

Kohlrausch determined the solubility by electrical conductivity measurements, and obtained values which differed somewhat according to the conditions of preparation. The average value, however, was 0.785 milli-equivalents, or 0.088 grm. per litre calculated as anhydrous salt. The solubility is greater in acetic acid than in water, the maximum being reached in approximately 4N acid.

An acid salt, barium binoxalate, Ba(HC₂O₄)₂, may be prepared in the anhydrous state, or with 1 or 2 molecules of water of crystallisation. It is more soluble in water than the neutral salt, and is decomposed by water unless excess of oxalic acid is present. For any one temperature there must naturally be a definite concentration in acid salt if both the solid phases, neutral salt and acid salt are present.