WATER. 203 



point the chemical process begins. Sodium has the 

 most intense affinity for oxygen, and therefore com- 

 bines with this element of the water, setting its hydro- 

 gen at liberty. No acid is required as in the case of 

 zinc. Metallic potassium may also be used in this 

 experiment. To avoid its ignition by contact with 

 the water, it is to be wrapped in paper, and the twisted 

 end of the wrapper used as a holder, with which to 

 thrust it under the mouth of the tube. 



WATER. 

 502. COMPOSITION. Many important 



Of what is , J _ 



water com- properties of water have already been il- 

 posed lustrated in the chapter on Vaporization. 



Others will be mentioned below. It is composed of 

 oxygen and hydrogen, as has already been proved both 

 by analysis and synthesis. These gases are condensed 

 in combination to about a^Vo- of their original volume. 

 It remains to show how the exact proportion in 

 which they enter into the composition of water is as- 

 certained. 



503. FIRST METHOD OF PROOF. One 



Describe the . 



method by gal- method is to decompose water by the gal- 

 vanic P rocess > and collect and weigh the 

 gases obtained. The oxygen is found to 

 weigh eight times as much as the hydrogen. Water 

 is thus shown to be composed of eight parts of oxygen, 

 by weight, to one part of hydrogen. In other words, 

 nine pounds of water contain eight pounds of oxygen 

 and one pound of hydrogen. 



