VII.] 



COMPOSITION OF PURE WATER. 



107 



placed a part of the hydrogen so energetically that sufficient 

 heat has been produced to ignite the gas thus set free. 



Certain other metals closely related to potassium will also 

 effect the decomposition of water, but the action is less 

 energetic than with potassium. The metal sodium, one 

 of the constituents of common " soda," rends the water 

 asunder, combining with its oxygen and turning out the 

 hydrogen ; but the liberated gas does not catch fire spon- 

 taneously, at least if the v/ater be cold. Cautiously hold a 

 piece of sodium under water by means of a little wire-gauze 



Fig. 27. — JJecumposition of water by means of sodium. 



spoon (Fig. 2 7), and bubbles of gas will immediately arise from 

 the neighbourhood of the metal ; this gas may be collected in 

 a small inverted vessel filled with water, and will be found 

 to burn with the characteristic flame of hydrogen. If a 

 fragment of sodium be thrown on to the surface of hot 

 water, it is at once surrounded by flame, just as the potas- 

 sium was, but the flame in this case is yellow, instead of 

 being violet-coloured. 



Potassium and sodium are metals but little known outside 

 the chemical laboratory. The decomposition of water may, 



