J22 



CHEMISTRY. 



vegetable matter decays under water, and hence its name, 

 marsh gas. You can very easily secure some of this gas 

 from the mud of a pond in the way shown in Fig. 46. 



A bottle filled with wa- 

 ter is held inverted in 

 the pond with a funnel 

 in its mouth, and the 

 mud is disturbed under- 

 neath with a stick. When 

 the bottle becomes filled 

 with gas, close it with a 

 cork before removing it 

 from the water. There 

 are two gases together in 

 the bottle carburetted 

 hydrogen and carbonic 

 anhydride. In order to get rid of the latter you must intro- 

 duce something which will combine with it, and not with the 

 carburetted hydrogen. It is done in this way : Pour a little 

 water into the bottle, and then introduce a piece of quick- 

 lime or of potassium hydrate, 

 and,quickly returning the cork, 

 shake the bottle a few minutes. 

 The carbonic anhydride is thus 

 made to unite with the calcium 

 or potassium, forming a carbon- 

 ate. Remove now the cork from 

 the bottle, with its mouth under 

 water. Some of the water will 

 go up into the bottle, to take the 

 place of the carbonic anhydride 

 Fig. 4T. which has disappeared. If now 



you apply a lighted match to the mouth of the bottle, the gas 

 will take fire and burn with a blue flame. By pouring water, 



