Barium hydroxide, it absorbs very little CO in aqueous solutions and is therefore insensitive to atmospheric fluctuations. This property is used in calibrating pH equipment. Volatile barium compounds burn with a green to pale green flame, which is an efficient test to detect a barium compound. The color results from spectral lines at 455.4, 493.4, 553.6, and 611.1 nm. Organobarium compounds are a growing field of knowledge: recently discovered are dialkylbariums and alkylhalobariums. Barium found in the Earth's crust is a mixture of seven primordial nuclides, barium-130, 132, and 134 through 138. Barium-130 undergoes very slow radioactive decay to xenon-130 by
Barium perchlorate yields the monohydrate. The anhydrous form is obtained by heating to 140 °C in vacuum. Dehydration of barium perchlorate that does not occur in vacuum will also result in hydrolysis of the perchlorate. Other reactions that produce barium perchlorate are as follows: perchloric acid and barium hydroxide or carbonate; potassium perchlorate and hydrofluosilicic acid followed with barium carbonate; boiling solution of potassium chlorate and zinc fluosilicate. For large-scale manufacturing purposes, barium perchlorate is synthesized by evaporating a solution of sodium perchlorate and barium chloride. Another method of preparation involves the digestion of a saturated solution of ammonium perchlorate with hydrated