154 PROCESS OF NUTRITION. CHAP. III. 



pable of supporting combustion : another candle 

 burned in it perfectly well.^ The experiment suc- 

 ceeded also with sprigs of Balm, and with plants of 

 Groundsel and Spinach, and the process seemed to 

 depend on the vegetating state of the plant; for 

 \vhendetached leaves only were introduced., they did 

 not ameliorate the air, though they were yet per- 

 fectly fresh. The ameliorating of a quantity of 

 vitiated air by means of confining a sprig of Winter 

 Savoury in it for five or six days was ascertained 

 also by the application of the eudiometer. Equal 

 measures of the confined atmosphere and nitrous 

 gas occupied a space equal only to 1 '275. Hence 

 the vitiated air was evidently ameliorated by the 

 plant. It does not, however, appear that Priestley 

 had yet discovered the rationale of the above ame- 

 lioration, whether it was by abstraction or extrica- 

 Who finds tion ; but he discovered some years afterwards that 

 pure or plants, when placed in water and exposed to the 



'*S nt f tne sun * ^ ve out wnat was tnen called pure 

 or dephlogisticated air. In the course of his ex- 

 periments on the growth of plants in water impreg- 

 nated with fixed air, he had observed air-bubbles 

 issuing spontaneously from the stalks and roots of 

 several plants growing in water that was not so im- 

 pregnated ; believing that the air thus extracted had 

 percolated through the plant, he thought he had 

 now discovered the clue that was to lead him infal- 

 libly to the ascertaining of the fact of the ameliora- 

 * On Air, vol. i. p. 60. 



