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 Rh giving it out again; still less of their affecting any change in its properties.

Dr. Priestley was the first who suggested this last-mentioned quality in vegetables. He ascertained their power of absorbing carbonic acid gas, denominated by him fixed air, and giving out oxygen gas, or pure respirable air. It was also his opinion that leaves imbibed the former by their upper, and gave out the latter by their under surface. He found some aquatic or marsh plants extremely powerful in this respect, especially the Willow-herb or Epilobium, and the Conferva, a minute branching cotton-like vegetable which grows in putrid water, and the production of which, in water become foul from long keeping on ship-board, Dr. Priestley judged to operate principally in restoring that fluid to a state fit for use.

Dr. Ingenhousz, pursuing Dr. Priestley's inquiries, found light to be necessary to these functions, and that in the dark leaves gave out a bad air. He observed moreover that fruits and flowers almost invariably gave out a bad, or carbonic, air, but more especially in the dark. He probably carries his