|^5 ON THE VEGETATION OF PLANTS. 



Opinion that We are indebted to Dr. Prieftley for the difcovery, that 



FgeiTtod-ie at- X " P^ ants expofed to light yield oxigenous air; and ever fince it 

 mofphcrc, has been made, an opinion has been adopted, that growing 



vegetables fupply the oxigenous portion of atmofpherical air, 

 of which there is a conftant confumption, by combuftion, fer- 

 mentation, refpiration, and the calcination of metals. 

 ill founded; If this fubjectis attentively examined, it will be found that 



plants have no effect in rendering the air of the atmofpherc 

 pure", 

 becaufe they af- Firfi. Whenever oxigenous gas has been obtained from ve* 

 ford none unlefs geta y es car bonic acid gas has been prefent. 



carbonic acid be G _. ' . n1 r & i r i • •• i • , 



prefent. Expe- Dr. Pneitley expoted plants to atmofpheric air, in which 

 riments of fpirit of wine and w T ax and tallow candles had burned out ; to 

 proof; a ^ r which had been vitiated by the death or putrefaction of mice 



and fifhes, and to air which had been frequently taken into his 

 lungs. He alfo obferved, that there was a flower and lefs pro- 

 duction of air from rain and diftilled, than from pump and ftag- 

 nant water, 

 and of the au- ^he difference between the quantity and quality of the gas, 

 thor; tabulated, obtained from river water and the fame water impregnated 

 with carbonic acid, by expofing plants in it to the influence of 

 folar light, will be feen by the following table : 



Leaves 



