BY LEAVES. 205 



more or less pure. The 'Nymphcea alba^ Engl. 

 Bat. ti l60, affords an extraordinary abun- 

 dance of it. Dr. Ingenhousz observed plants 

 to be very various in their mode of emitting 

 these bubbles, but it was always uniform in 

 the same species. Air collected from water 

 placed in similar circumstances without plants, 

 proved not oxygen, but much worse than 

 common air, viz. carbonic acid gas, which 

 following chemists have confirmed, and which 

 we have already mentioned. Ingenhousz also 

 found the air collected from plants under 

 water in the dark worse than common air, 

 especially that from walnut-leaves ; which 

 confirms the common opinion, above alluded 

 to, respecting this tree. 



Plants purify air very quickly. A vine- 

 leaf in an ounce phial of carbonic acid gas, 

 that immediately extinguished a candle, 

 placed in the sun, without watery changed it 

 to pure respirable air in an hour and half. 

 Dr. Priestley found plants to alter even un- 

 mixed inflammable air, or hydrogen, espe- 

 cially the Epilobium liirsutum, if I mistake 

 not, and Polygonum Ilydropiper. 



Succulent plants are found to afford most 



