CHEMISTRY OF THE EARTH 91 



valency by a kind of internal union of certain 

 of their valencies, much in the same way 

 as it was pointed out above that two atoms 

 of hydrogen unite to satisfy each other in the 

 absence of more powerful attractions of other 

 elements. For example, nitrogen and phos- 

 phorus are pentavalent atoms which possess 

 five dynamic centres of energy capable of 

 forming combinations. But in the majority 

 of their compounds, two of these dynamic 

 centres set up internal attractions or pertur- 

 bations in regard to each other, as a result 

 of this the nitrogen or phosphorus is left with 

 three free dynamic centres, and possesses an 

 apparent valency of a trivalent element. 

 A similar effect is often seen between 

 two atoms of a polyvalent element. For 

 example, two carbon atoms may come 

 into energy relationship by two of their 

 dynamic centres or valencies and, as a result, 

 although each carbon atom possesses four 

 valent positions, the two atoms after this 

 union of themselves have only two centres 

 left upon each atom, or four in all, and a com- 

 pound is formed of two atoms of carbon with 

 four of hydrogen, the well-known olefiant 

 gas. 



In settling valencies, the greatest caution 

 has accordingly to be observed by the chemist. 



