224 Experiments on the Production of Air 



sediment (the green matter of Dr. Priestley) beginning 

 to be found upon the bottom of the jar, it began to 

 yield air in abundance, and continued to furnish it in 

 pretty large quantities till about the eighteenth day, when 

 it appeared to be exhausted. 



Why the water should turn green in this experiment, 

 and not in the last, I know not ; unless it was in conse- 

 quence of the large^ surface of water in the cylindrical 

 jar which was exposed to the air in this experiment ; or 

 in consequence of the sun's shining directly upon the 

 bottom of the vessel where the sediment was formed. 



In the former experiment, the bason in which the jar 

 was inverted was but just big enough to admit the jar; 

 and as the jar was cylindrical, the surface of the water 

 exposed to the atmosphere in the bason was but very 

 small ; and the bason being very thick, and formed of 

 glass which, though of the white kind, was of an inferior 

 quality, and very imperfectly transparent, as I have al- 

 ready observed, the bottom of the bason where the sed- 

 iment was formed was but very imperfectly illuminated. 



Having never been thoroughly satisfied with respect to 

 the origin of the dephlogisticated air produced upon ex- 

 posing fresh vegetables in water to the action of the sun's 

 rays, according to the method of Dr. Ingen-Housz, my 

 doubts with respect to the opinion generally entertained, 

 of its being elaborated in the vessels of the plant, instead 

 of being removed, were rather confirmed by the result 

 of these experiments ; and however disposed I was to 

 adopt the beautiful theory of the purification of the at- 

 mosphere by the vegetable kingdom, I was not willing 

 to admit a fact which has been brought in support of it, 

 till it should appear to me to have been proved by the 

 most decisive experiments. 



