"When oxygen was discovered by Priestley and Scheele, it was regarded by them as air altogether respirable, and exhibiting a maximum power of supporting combustion, because it was quite free from phlogiston. It was named accordingly de-phlogisticated air, and for a season the atmosphere was referred to as consisting of two parts, a "dephlogisticated part" and a "phlogisticated part," which differed... only in degree. By-and-by those parts were regarded as differing in kind, not merely in degree; the dephlogisticated part, or dephlogisticated air, being our oxygen, and the phlogisticated part or air, our . Cavendish's enquiry began before this later view became general."