24 Pure Air -produced by Plants in Water. [Book VIII, 



found that plants yield much more vital air in diftilled 

 water impregnated with fixed air, than in fimple diftilled 

 waser. 



It appears further, from the experiments of Dr. 

 Prieftley, that plants will bear a greater proportion of 

 inflammable than of fixed air, and that vital air ap- 

 peared generally injurious to plants. A.fprig of mint 

 growing in water, placed over a fermenting liquor, and 

 of courfe expofed to fixed air, became quite dead in 

 one day ; a red rofe became of a purple colour in 

 twenty four hours. Plants die very foon both in ni- 

 trous air, and in common air when faturated with it. 

 Air appears uniformly to have been purified by heakhy 

 plants vegetating in it ; but thefe experiments require 

 great nicety, as the lead degree of putrefaction will 

 injure the air. The -air contained in the bladders of 

 marine plants was found confidcrably purer than com- 

 mon air. 



Armofpheric air is reftored, after being injured by 

 refpiration or combuftion, by a plant vegetating in it. 

 This reiteration of air depends upon the vegetating 

 ftate of the plant; for a number of mint-leaves- frefh 

 gathered being kept in air in which candles had burnt 

 out, did not reftore the air. Any piant will effect this 

 purpofe, but thofe of the quickeft growth in the moil 

 .rious manner. 



That plants have a proper' y of producing pure air 



from water is evident from an experiment of Dr. 



Prieftley. The green matter which is to be obferved 



.i-.er is doubtiefe a vegetable production. Water 



containing this green matter always afforded vital air 



in a-largv: quantity, but water which had it not afforded 



none. It has been frequently- rbferved that vegetables 



do not thrive in the dark, A receiver was therefore 



j with water, and kept till it was in aftate of giving 



air 



