from Water exposed to Light. 217 



last experiment was made), gave Z-^Q cubic inches of 

 air, whose quality was i a -J- 3 n = 1.20, or 280. 



Experiment No. 21. 



A small globe (contents, 20 cubic inches),, with 17 

 grains of raw silk, exposed at the same time, give i 

 cubic inch of air, which turned out i a -j- 3 n ==. 1.37, or 

 263. 



Experiment No. 22. 



A large globe, containing 296 cubic inches, being filled 

 with fresh water and a small quantity of conferva rivularis, 

 and exposed at the same time with the three globes above 

 mentioned, gave i| cubic inch of air, which, proved with 

 nitrous air, gave i a -\- i n 1.76, or 124. 



The water, in this experiment, was changed to a brown 

 colour, owing, as I conceived, to the too great heat the 

 conferva acquired in the sun. 



These experiments were made between the 2d and the 

 5th of July (1786). 



Experiment No. 23. 



Surprised at the smallness of the quantity, and the 

 inferior quality, of the air produced in the last experi- 

 ment, I was induced to repeat it ; accordingly, the globe 

 being again filled with water and a quantity of fresh 

 conferva rivularis (a small handful), and being exposed to 

 the action of the sun's rays during 3 fine days, i3yVo 

 cubic inches of air were produced, which, proved with 

 nitrous air, gave i a -\- 3 n = 1.54, or 246. 



At the end of the experiment, the water appeared to 

 be very faintly tinged of a greenish cast. 



The two following experiments were made upon the 

 2oth and 2ist of August. 



