282 Observations on

mately diffused through a quantity of noxi-ous air, would much sooner imbibe thephlogiston with which it was charged z andseveral persons, particularly Mr. Keir, haveeven thought that the melioration of air byvegetation may be owing to the exhalationof moisture from plants in a vegetating state.I was very willing to adopt that idea myself,in preference to my own, which was thatplants imbibe the phlogiston with whichthe air is overcharged into their substance,and convert it into their proper nourish-ment. But when I tried the effects of steamon phlogisticated air, with as much at-tention as I could give to the experiments,I never found that it was at all mended bythe process.

I first took a quantity of air that had beenphlogisticated by a mixture of iron filingsand brimstone, and introducing into it theend of a glass tube, communicating with aphial, which I had filled with water, Ikept it in a boiling heat, about a quarter ofan hour, in which time the steam hadeffectually pervaded the mass of air, having

made