156 PURIFICATION" OF AIR BY LEAVES. 



same water, and placed the whole together in the sun- 

 shine. From their under sides came streams or bubbles 

 of air, which collected in the inverted bottom of each 

 jar. The air thus procured proved oxygen gas, more 

 or less pure. The Nymphda alha^ Engl. Bot. t. 1 60, 

 affords an extraordinary abundance of it. Dr. Ingen- 

 housz 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. car- 

 bonic acid gas, which following chemists have con- 

 firmed, and which we have already mentioned. Ingen- 

 housz 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 ex- 

 tinguished a candle, placed in the sun, without water, 

 changed it to pure respirable air in an hour and half. 

 Dr. Priestley found plants to alter even unmixed in- 

 flammable air, or hydrogen, especially the Epilobium 

 hirsutumy if I mistake not, and Polygonum Hydropipcr. 



Succulent plants are found to afford niost air, in 

 consequence of the abundance of their Cellular Inte- 

 gument, or Parenchyma, in which, as I have hinted 

 in the fourth chapter, the chemical operations of the 

 leaves are performed. 



