VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 209 



which many aquatic plants were growing, and was exposed in the same place, 

 and during the same period. This water had a very faint greenish cast. The 

 pond from which it was taken is fed by a large river, the Isar, which runs by the 

 town. 



The 2d day after these waters had been exposed in the sun, a small quantity 

 of air had collected itself at the upper part of each of the jars. The 3d, 4th, 

 and 5 th days, the pond water furnished air in pretty large quantities ; and it went 

 on to yield it without intermission, when the sun shone on it, till the 14th day, 

 when it seemed to be nearly exhausted. I continued the experiment however 

 till the 28th day, though during the last fortnight the quantity of air in the jar 

 did not appear sensibly to be increased. 



The spring water, during the first 5 or 6 days, furnished very little air : and 



it was not till the 14th day that it began to yield it in any considerable quantities. 



From this time it went on to furnish it, though but very slowly, till about the 



22d day, when it ceased, appearing to be quite exhausted. On the 28th day I 



removed the airs from the jars, when I found their quantities and qualities to be 



as follow : 



Quantity. Quality. 



A.ir furnished by the spring water 14 cubic inches la + 2n = 1.62, or 138 

 by the pond water 31^ lo + 3» = 1.48, ov 252 



Neither the colour of the spring water, nor that of the pond water, appeared 

 to be sensibly changed ; but both had deposited a considerable quantity of earth, 

 which was found adhering to the surfaces of the glass basins in which the jars 

 were inverted. As these basins were rather deep, and as they were very thick 

 in glass, and consequently not very transparent, their bottoms, where the sedi- 

 ment of the water was collected, were in a great measure obscured or deprived 

 of the direct rays of the sun. Suspecting that this circumstance might have 

 had some effect, so as to have hindered the water from furnishing so much air 

 as otherwise it might have yielded, to satisfy myself respecting this matter I re- 

 peated the experiment, disposing the apparatus in such a manner, that the sedi- 

 ment 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. 



Exper. 28. In a large cylindrical jar, of very fine transparent glass, 10 inches 

 in diameter, and 1 2 inches high, filled with spring water, I inverted a conical 

 glass jar, Qf 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 1^4-372= 1.87, or 213. 



The water in this experiment furnished very little air till the 7th day ; but 

 after that time, having assumed a faint greenish cast, and a fine greenish slimy 



VOL. XVI. £ E 



