CHEMISTRY OF THE EARTH 97 



is in equilibrium with four univalent atoms 

 or their equivalents. Such equivalents may 

 be legion, and so long as the carbon atom 

 has four centres of activity satisfied by four 

 such centres outside itself, it is saturated and 

 in equilibrium. Failing outside attractions 

 two of the four may enter into interplay with 

 each other, and, such a carbon atom is then 

 spoken of as an unsaturated carbon atom. 

 The name is in reality a misnomer, for it is 

 saturated, except when something of superior 

 affinity presents itself, and then the two 

 dynamic centres which were previously play- 

 ing upon each other, enter into relationship 

 with the new body. For example, the com- 

 pound called carbon-monoxide which forms 

 the poisonous constituent of coal gas, or in the 

 gas from a charcoal fire, or brick-kiln or lime- 

 kiln, is such an unsaturated compound with 

 one tetrad atom of carbon united to the 

 dyad atom of oxygen, and the other two 

 affinities of the carbon atom more feebly 

 satisfying each other by self interplay of 

 energy. If now, this gas be mixed with 

 chlorine gas the chlorine interacts spontan- 

 eously with the two carbon affinities which 

 were previously interacting with each other, 

 and each of these now comes into dynamic 

 interplay with a chlorine atom. As a result, 



