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and by their decomposition they rapidly destroy the 

 oxygene of the air. In some of the early experiments 

 of Dr. Priestley before he was acquainted with the 

 agency of light upon leaves, air that had supported 

 combustion and respiration, was found purified by the 

 growth of plants when they were exposed in it for suc- 

 cessive days and nights ; and his experiments are the 

 more unexceptionable, as the plants, in many of them, 

 grew in their natural states ; and shoots, or branches 

 from them, only where introduced through water into 

 the confined atmosphere. 



I have made some few researches on this subject, 

 and I shall describe their results. On the 12th of 

 July, 1 800, I place a turf four inches square, clothed 

 with grass, principally meadow fox-tail, and white 

 clover, in a porcelain dish, standing in a shallow tray 

 filled with water ; I then covered it with a jar of flint 

 glass, containing 380 cubical inches of common air in 

 its natural state. It was exposed in a garden, so as 

 to be liable to the same changes with respect to light 

 as in the common air. On the 20th of July the results 

 were examined. There was an increase of the volume 

 of the gas, amounting to fifteen cubical inches ; but the 

 temperature had changed from 64 to 71; and the 

 pressure of the atmosphere, which on the 12th had 

 been equal to the support of 30.1 inches of mercury, 

 was now equal to that of 30.2. Some of the leaves of 

 the white clover, and of the fox-tail were yellow, and 

 the whole appearance of the grass less healthy than 

 when it was first introduced. A cubical inch of the 

 gas, agitated in lime-water, gave a slight turbidness to 



