from Water exposed to Light. 193 



free it of air ; and inverting the globe under water, and 

 placing its neck in a glass jar containing a quantity of the 

 same water with which the globe was filled, I exposed it 

 in my window to the action of the sun's rays, and pre- 

 pared myself to examine the progress of the generation 

 or production of the air. 



The globe had not been exposed ten minutes to the 

 action of the sun's rays, when I discovered an infinite 

 number of exceedingly small air-bubbles, which began to 

 make their appearance upon the surface of the silk ; and, 

 these bubbles continuing to increase in number and in 

 size, at the end of about two hours, the silk, appearing 

 to be entirely covered with them, rose to the upper part 

 of the globe. 



These bubbles going on to increase in size, and run- 

 ning into each other, at length began to detach them- 

 selves from the silk, and to form a collection of air in 

 the upper part of the globe ; but, the measure of my 

 eudiometer being rather large, it was not till after the 

 globe had been exposed in the sun near four days, that 

 a sufficient quantity of air was collected to make the ex- 

 periment with nitrous air, in order to ascertain its good- 

 ness by that test. 



Having at length collected a sufficient quantity of this 

 air for that purpose, I carefully removed it from the 

 globe, and mixing with i measure of it 3 measures of 

 nitrous air, they were reduced to 1.24 measures ; which 

 shews that it was actually dephlogisticated air^* and of a 

 considerable degree of purity. 



Common air, tried at the same time, i measure of it with 

 I measure of nitrous air were reduced to 1.08 measure. 



* It must be remembered that this was written in the year 1786, at which period 

 this elastic fluid was generally denominated dephlogisticated air. 

 VOL. I. 13 



