114 CHEMISTRY. 



We have in this experiment an illustration of both decomposition and 

 composition produced by the agency of heat. The water is decomposed, 

 its two elements, oxygen and hydrogen, being separated from each other ; 

 and there is composition, for the oxygen, as it leaves the hydrogen, unites 

 with the iron to make an oxide of that metal. The oxidation, which is 

 produced slowly in ordinary temperatures, is here produced quickly by heat. 

 It is a curious fact that precisely the reverse of this action may be made to 

 occur. If hydrogen gas be passed through a gun-barrel heated red-hot, and 

 containing oxide of iron, it will take the oxygen from the iron, forming wa- 

 ter, which will issue in steam from the barrel. In the former experiment 

 you have steam entering one end of the barrel and hydrogen issuing from 

 the other, and the iron in the barrel is oxidized ; in the latter you have hy- 

 drogen entering at one end, and steam discharged from the other, and the 

 oxide of iron in the barrel is deoxidized. 



143. A Better Method. You can obtain hydrogen from 

 water without having this great amount of heat applied, 

 and therefore with a less cumbrous apparatus, as seen in 

 Some bits of zinc or of iron are put in water in a 



Fig. 38. 



bottle, and sulphuric acid is poured in through the funnel 

 tube. An effervescence at once appears, occasioned by the 

 gas as it is produced from the water ; and you must be care- 

 ful not to pour in too much, lest the heat generated by mix- 

 ing the strong acid with the water crack the glass bottle, 



