from Water exposed to Light. 223 



Neither the colour of the spring-water, nor that of the 

 pond-water, appeared to be sensibly changed ; but both 

 the one and the other of these waters had deposited a 

 considerable quantity of earth, which was found adhering 

 to the surfaces of the glass basons in which the jars were 

 inverted. 



As these basons were rather deep, and as they were 

 very thick in glass, and consequently not very transpar- 

 ent, their bottoms, where the sediment of the water was 

 collected, were, in a great measure, obscured, or deprived 

 of the direct rays of the sun. Suspecting that this cir- 

 cumstance might have had some effect, so as to have 

 hindered the water from furnishing so much air as other- 

 wise it might have yielded, to satisfy myself respecting 

 this matter, I repeated the experiment, disposing the ap- 

 paratus in such a manner that the sediment of the 

 water which attached itself to the bottom of the vessel 

 in which the jar was inverted had the advantage of being 

 perfectly illuminated. 



Experiment No. 28. 



In a large cylindrical jar, of very fine transparent 

 glass, 10 inches in diameter, and 11 inches high, filled 

 with spring-water, I inverted a conical glass jar, 9^ inches 

 in diameter at the bottom, and containing 344 cubic 

 inches, filled with the same water ; and exposed the 

 whole 21 days in a window fronting the south. 



The quantity of air produced amounted to 40 cubic 

 inches ; and its quality, proved by the test of nitrous 

 air, gave i a -f- 3 n = 1.87, or 213. 



The water, in this experiment, furnished very little air 

 till the seventh day ; but after that time, having as- 

 sumed a faint greenish cast, and a fine greenish slimy 



