COMPOSITION OF WATER 



37 



vapour into a trough of water. Note whether the iron filings 

 become changed in appearance. Note, also, whether the 

 escaping gas condenses in the water of the trough like steam, 

 or whether it is a permanent gas. If the latter, collect some 

 in an inverted tube of water, and study its properties. Is it 

 a supporter or non-supporter of combustion, and is it com- 

 bustible ? Is the change in the iron due to its having com- 

 bined with one element of the water, the other element, which 

 from its source might be termed "hydrogen" — i.e. water 

 producing — gas, being liberated ? If so, water is a compound 

 of this hydrogen with the element with which the iron has 

 confbined. If — 



water -}- iron = (iron + x) + hydrogen, 

 water = hydrogen + x. 

 The iron compound exactly resembles that which is obtained 

 by heating iron in air, and it may therefore be an oxide of 

 iron. If so, water must be oxide of hydrogen. An easy 

 method of testing this supposition will be to burn hydrogen 

 in air, when — since combustion in air consists in combination 

 with the oxygen — water should be formed. For this purpose, 



Fig. 21. 



prepare some hydrogen gas in the apparatus figured, by pouring 

 cold dilute sulphuric acid ( i of acid to 6 of water) through the 

 thistle funnel on to some granulated zinc placed in the flask A. 



