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CHAPTER XVII 



THE CHEMICAL RELATIONS OF WATER 



194. In Chapter xin oxygen was shown to be present 

 in air to the extent of some 20 % of that substance. 

 This element is also contained in water, eight-ninths 

 of the latter by weight consisting of oxygen. The 

 remainder of the water consists of hydrogen, an element 

 known in the free state as a colourless gas. 



EXPERIMENT 129. Drop a very small piece of 

 sodium (see Experiment 117) on the surface of a large 

 quantity of water contained in an earthenware trough. 

 The sodium floats, moving about on the top of the 

 water as a small molten ball, and making a hissing 

 noise as it does so. The ball slowly gets smaller, and 

 finally the sodium entirely disappears. We have 

 already discovered that sodium combines with oxygen 

 with great vigour. During its wanderings on the 

 water surface it has been combining with the oxygen 

 of the water and part of the hydrogen, the remainder 

 of the latter escaping into the air. Sodium hydroxide is 

 formed as a result of the combination, and its presence 

 in solution may be shown by dipping a red litmus paper 

 into the water after all action has ceased. 



The evolution of the hydrogen may be rendered 

 more readily apparent if the free movement of the 

 sodium be prevented by dropping it on a sheet of 

 filter-paper floating on the water. The heat produced 

 by the chemical action is thus concentrated in one 

 place, and the temperature produced is sufficient to 



