86 ORIGIN AND NATURE OF LIFE 



two separate molecules of water are formed. 

 This is the way the matter must be put to 

 render it readily understandable. As a matter 

 of fact, for any such chemical reaction, thous- 

 ands of millions of molecules of hydrogen 

 and oxygen are ruptured simultaneously, but 

 the above statement represents the propor- 

 tions in which the molecules are concerned. 



The second main characteristic of valency 

 is also illustrated in the above example. It 

 is to be noticed that two atoms of hydrogen 

 are required to each atom of oxygen. The 

 atom of oxygen has double the valency of the 

 atom of hydrogen, in this reaction. In the 

 formation of ammonia, as union of one atom 

 of nitrogen with three of hydrogen occurs, the 

 nitrogen atom has treble the value of the 

 hydrogen atom, and, in the other example 

 given above of marsh gas, the carbon atom 

 possesses four times the valency of hydro- 

 gen. 



A number of elements exist which possess 

 the same valency as hydrogen, such as 

 chlorine mentioned above, which unites atom 

 for atom with hydrogen to form hydro- 

 chloric acid, and the same is true of the 

 other members of the chlorine family, namely, 

 fluorine, bromine and iodine, which similarly 

 unite atom for atom with hydrogen to form 



