The Collaborative International Dictionary
Empyreal air
Empyreal \Em*pyr"e*al\, a. [L. empyrius, empyreus, fiery, Gr. ?, ?, in fire, fiery; ? in + ? fire. See In, and Fire.] Formed of pure fire or light; refined beyond a["e]rial substance; pertaining to the highest and purest region of heaven.
Go, soar with Plato to the empyreal sphere.
--Pope.
Empyreal air, oxygen gas.
Wiktionary
empyreal air
n. (context obsolete English) oxygen gas