"Black demonstrated that the fixed or solidified air did not merely increase the bulk and weight of the solid, but determined in a most striking manner its chemical properties, so that a substance which, when saturated with a peculiar air, was a bland, innocuous insoluble powder, or crystalline solid, became by the expulsion of this air soluble, caustic, and corrosive; and the difference between or on the one hand, and quicklime on the other, was shown to be entirely dependent on the presence or absence of the gas, which Black named fixed air, and we name '."