2 20 Experiments on the ProdzictioJi of Air 



Experiment No. 16. 



Concluding that if silk and other bodies, used in the 

 foregoing experiments, actually did not contribute any- 

 thing considered as chemical substances, in the process of 

 the production of pure air yielded by water ; but if, on 

 the contrary, they acted merely as a mechanical aid, in the 

 separation of the air from the water, by affording a con- 

 venient surface for the air to attach itself to, ■ — in this 

 case, any other body having a large surface, and attract- 

 ing air in water, might be made use of instead of silk in 

 the experiment, and pure air would be furnished, though 

 the body so made use of should be totally incapable of 

 communicating anything whatever to the water. 



To ascertain this fact, washing the great globe (con- 

 taining 296 cubic inches) perfectly clean, and filling it 

 with fresh spring-water, I introduced into it a quantity 

 of the fine flexible thread of glass, commonly called 

 spun glass, such as is used for making brushes for clean- 

 ing 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 has 

 grown 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 anything 

 to the water. 



The result of the experiment was, that, the globe 

 being exposed in the sun, air-bubbles began almost im- 

 mediately to make their appearance upon the surface of 

 the spun glass, and in four hours -^-^-^ of a cubic inch of 



