8 METHOD OF COLLECTING GAS. 



marked by the dotted lines c (this may be a common 

 pail, or shallow water tub). A tumbler or other con- 

 venient vessel is now filled with water, and inverted 

 under the surface, so that it may contain no air, being 

 filled entirely with water : it is then brought carefully 

 over the orifice of the tube, and the ascending bubbles 

 of gas displace the water until it is entirely driven out, 

 the gas remaining confined. If a little shelf, hollowed 

 somewhat underneath, and with a hole through it at 

 the highest point of the hollow, be placed in the cis- 

 tern, three or four vessels in succession may be filled 

 over this hole and set aside for use, keeping the mouths 

 always under water. A common tub of a shallow 

 form will answer the purpose of a cistern. 



I have been thus particular in describing this little 

 apparatus of the cistern, because all of the other gases 

 concerning which we are to study may be received in 

 the same way. It is perfectly eflfective, yet at the 

 same time simple and cheap. 



The hydrogen being thus collected, w^e are next to 

 ascertain what are its properties. 



1. It is inflammable : if a lighted taper be plunged 



into a jar of it, the gas will instantly take fire, and 



burn with a pale flame. This may also be shown by 



Pi ^ removing the cork from the bottle a 



in fig. 1, and substituting another cork 



with a short tube coming to a point 



as fig. 2. A match will kindle the 



jet of gas issuing from the orifice a, 



and it will continue to burn so long 



as the generation of gas within the 



bottle is active. 



2. Although inflammable itself, it 

 is not a supporter of combustion. The 

 [^ taper which kindles a jar of it, is it- 

 self extinguished. 

 3. It is much lighter than common air, being the 



