LAW OF DIFFUSION. 



115 



in one neck of a two-necked bottle at a lower level : through the 

 other neck passes another piece of glass tube (6) reaching to the 

 bottom of the bottle, and 

 terminating upwards in a 

 drawn-out point or jet (fig. 

 64). If a large jar of 

 hydrogen be now placed 

 over the porous pot, the 

 gas will diffuse inwards 

 through the sides of the 

 pot so much more rapidly 

 than the contained air will 

 pass outwards, that a con- 

 siderable increase of pres- 

 sure results ; the effect of 

 which is to force the water 

 with which the two-necked 

 bottle is half filled upwards 

 through the jet, forming a 

 fountain. If all the junc- 

 tions are properly air-tight, 

 the stream of water may 

 be made to rise some 8 

 or 10 inches in the air 

 with properly proportioned 

 tubes, &c. 



Ordinary coal gas may 

 be substituted for hydro- 

 gen, with somewhat inferior 

 results. 



Expt. 110. Diffusion of 

 Carbon Dioxide less Rapid 

 than that of Air. By 

 means of the flexible joint 

 at c (fig. 64), the poroua Fi S" 64 ' Diffusion of Hydrogen, 



pot may be made to hang downwards; if now a vessel full 

 of carbon dioxide (filled as in Expt. 101) be so placed that the 

 pot hangs into it, air will diffuse outwards from the pot, and 

 carbon dioxide inwards; the latter gas, however, passes much 

 more slowly than the former, so that a diminished pressure now 

 results inside the arrangement; in consequence, air is sucked 

 upwards from the two-necked flask, and bubbles of air are 

 accordingly drawn into it from the outside atmosphere through 

 the tube b. 



