£lf C8EMICAL ACTION OF 



been confirmed, extended in a variety of 

 ways, or explained on the principles of im- 

 proved chemistry, by Dr„ Percival and Mr* 

 Henry in England, Dr. Woodhouse in Ame- 

 rica, and M. Sennebier and M. Theodore de 

 Saussure, as well as various other philoso- 

 phers, on the continent of Europe. It is 

 agreed that in the day-time plants imbibe 

 from the atmosphere carbonic acid gas, 

 (which was formerly called fixed air, and is 

 an union of oxygen and carbon), that they 

 decompose it, absorb the carbon as matter of 

 nourishment which is added to the sap, and 

 emit the oxygen. So they absorb the same 

 gas from water, when it is separated from 

 that fluid by the action of light. The burn- 

 ing of a candle, or the breathing of animals, 

 in confined air, produces so much of this gas, 

 that neither of these operations can go on 

 beyond a certain time, but the air so conta- 

 minated serves as food for vegetables, whose 

 leaves, assisted by light, soon restore the oxy- 

 gen, or, in other words, purify the air again. 

 This beautiful discovery, for the main prin- 

 ciples of which we are indebted to the cele- 

 brated Dr. Priestley, shows a mutual depend- 



