Arsenic acid is the chemical compound with the formula H₃AsO₄. More descriptively written as AsO(OH)₃, this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but only found in solution where it is largely ionized. Its hemihydrate form (H₃AsO₄·½H₂O) does form stable crystals. Crystalline samples dehydrate with condensation at 100 °C.