322 DIFFUSION OF GASES. 



mix even if the lighter of two gases is on the top of the 

 heavier, as maybe shown with carbonic acid gas. Tim 

 gas is about one and a half times as heavy as atmo 

 spheric air, and differs also from the latter in not bein^ 

 a supporter of combustion : a burning splinter of wooc 

 is immediately extinguished when introduced into it. 



Carbonic acid may be collected by placing the moutl 

 of the tube leading from the generating apparatus closi 

 to the bottom of a tall and wide glass vessel. The ga 

 being heavier than air, collects at the bottom of th 

 vessel, and rises gradually until it has completely fille< 

 it. The depth to which the gas has risen may b 

 easily ascertained by inserting a burning splinter. ] 

 the vessel is quite full, the flame will be extinguishe 

 when the splinter dips only a very short distance belo 1 

 the top of the vessel ; but if it is not quite full, t\i 

 splinter will not be put out until it is immersed t 

 some depth that is, until it actually dips into the ga 

 That carbonic acid is heavier than air may be well show 

 by the fnct that it may be poured from one vessel im 

 another like a liquid: a piece of burning candle is place 

 in a vessel ; another vessel, of about the same size, 

 filled with the invisible gas, and held obliquely over tl 

 first vessel in the same manrer as in pouring out 

 liquid : the heavy gas flows into the other vessel ai 

 extinguishes the candle. 



This experiment can of course be made only in a room with cloe 

 -windows and door ; the slightest draught drives the gas to the si 

 of the vessel. The vessels should be rather tall, about 'JO m high a 

 12 cm wide. The small piece of candle or taper may be fixed to i 

 bottom of the vessel, or attached to a piece of cork, which, if nee 

 sary, should be hollowed out below, so as to adapt it to the asua 

 curved form of the bottom of glass vessels. 



