CHEMISTRY OF THE EARTH 85 



enormous variations are found, and when a 

 number of various claimants for chemical 

 union are present, as for example, in a 

 world cooling down in space, the varying 

 amounts of different chemical compounds 

 formed and their variety will depend on the 

 amounts and affinities of the constituents 

 present. 



In these questions of affinity two factors 

 come in, there is always an affinity to be over- 

 come, as well as the one which is satisfied as 

 the result of the chemical action between 

 the two substances or elements. It is rarely 

 that the atoms of an element exist singly in 

 nature. When such elemental atoms cannot 

 find other dissimilar atoms to unite with 

 they unite with each other, usually in pairs. 

 These pairs must be sundered on both sides 

 before union of the two different kinds of 

 element can take place. For example, it is 

 not really two atoms of hydrogen and one 

 atom of oxygen that unite to form a molecule 

 of water. But two molecules of hydrogen, 

 each containing two atoms of that element, 

 and one molecule of oxygen, likewise con- 

 taining two atoms of oxygen, have to be 

 severed first, and then, when freedom has 

 been obtained, each atom of oxygen becomes 

 attached to two atoms of hydrogen, so that 



