THE CHEMISTRY OF WATEE. HYDROGEN. 



113 



Fig. 37. 



posed by reason of the attraction of oxygen and iron for 

 each other. The oxygen of the water unites with the iron, 

 forming an oxide of iron. This leaves the other constitu- 

 ent of water, hydrogen, to pass on alone. It issues at the 

 other end of the barrel, and is conducted off by a bent tube, 

 to be collected in jars in the usual manner. This reac- 

 tion, expressed in the symbolic language of chemistry, is 

 written thus : 4H 2 O+Fe 3 =Fe 3 O 4 +8H. Hydrogen would 

 not be formed if water were merely poured through the 

 barrel. Neither would it if steam pass through, unless the 

 iron turnings be heated to a high degree. You see, then, 

 that a very great heat is required to make the iron decom- 

 pose the water, or, in other words, to make the oxygen quit 

 the hydrogen and unite with the iron. The object of hav- 

 ing iron turnings in the barrel is to allow the steam to come 

 in contact with a very extensive surface of iron. Bundles 

 of knitting-needles are sometimes used, and, instead of a 

 gun -barrel, a piece of iron gas -pipe. If the barrel were 

 empty, but little of the steam would be decomposed. As it 

 is, some steam may pass through unchanged ; but if it does 

 it is condensed in the water of the pneumatic trough, and 

 does not pass on with the hydrogen into the receiving jar. 



