208 PHILOSOPHICAL TRANSACTIONS. [anNO 1787. 



furnished, though the body so employed should be totally incapable of commu- 

 nicating any thing whatever to the water. 



To ascertain this fact, washing the great globe (containing 296 cubic inches) 

 perfectly clean, and filling it with fresh soring water, I introduced into it a quan- 

 tity of the fine flexible thread of glass, commonly called spun glass, such as is 

 used for making brushes for cleaning jewels, and for making a kind of artificial 

 feather frequently sold by the Jew pedlars. This spun glass is no other than 

 common glass drawn out, when hot, into an exceeding fine thread ; which 

 thread, in consequence of its extreme fineness, retains its flexibility after it is 

 cold. I made choice of this substance not only on account of its great surface, 

 but also on account of the strong attraction which is known to subsist between 

 glass and air, and the impossibility of its communicating any thing to the water. 



The result of the experiment was, that the globe being exposed in the sun, 

 air-bubbles began almost immediately to make their appearance on the surface 

 of the spun glass, and in 4 hours -^-^ of a cubic inch of air was collected, 

 which, proved with nitrous air, gave la -}- ln= 1.12, or 88 ; after which, not 

 a single air-bubble more was produced, though the globe was exposed a whole 

 week in the window, during which time there were several very warm, fine, sun- 

 shiny days. 



This experiment shows evidently, that something more is wanting to the pro- 

 duction of pure air by water, exposed in the sun, than merely a surface to which 

 the air dissolved in the water can attach itself, in order to its making its escape. 

 The air furnished in this experiment was doubtless merely that with which the 

 water issuing from the earth was overcharged, and which would have made its 

 escape from the water, had this, instead of being exposed with the spun glass 

 in the sun, been simply left for some time exposed to the free air of the 

 atmosphere. 



It appears that this air, naturally existing in spring water, instead of being 

 dephlogisticated is something worse than common air ; and this agrees with the 

 observations of Dr. Priestley, and seems to justify his opinion with respect to 

 the cause of the fertility of lands washed by waters issuing from the earth. If 

 the above experiment shows that something is wanted to be mixed with water, 

 in order to enable it to yield pure, when exposed to the action of the sun's light, 

 the following show, that this something, whatever it may be, is frequently to 

 be found in the water itself, in its natural state. 



Exper. 27. A large jar of clear white glass, containing 455 cubic inches, 

 being washed very clean, was filled with fresh spring water, and inverted 

 in a glass basin of the same, and placed .in the middle of the garden of the 

 Elector's palace, where it was left exposed to the weather 28 days. At the same 

 time another like jar was filled with water, taken from a pond in the garden, in 



