CARBONIC ACID 147 



phoric acid (after its first hydrogen has been 

 neutralized by base), has the remarkable 

 property of preserving a neutral reaction 

 whenever it exists in solution with its salts, 

 provided there be an excess of acid. All acids 

 whose strength is even a little either greater 

 or less than carbonic acid lack the property. 1 



This characteristic of carbonic acid is of 

 the utmost significance, first by regulating 

 one of the most fundamental of physico- 

 chemical conditions, and secondly by pre- 

 serving throughout nature the characteristic 

 chemical inactivity of water, which disappears 

 whenever the reaction becomes either appre- 

 ciably acid or appreciably alkaline. Almost 

 the only case of important geological action 

 due to acidity or alkalinity of water is the 

 action of fresh water, containing carbonic acid 

 itself, to weather the rocks. This process is, 

 however, self -limited, for the dissolved material 

 forms bicarbonates, and thus at once pro- 

 vides permanently inactive balanced solutions. 



It is impossible to understand the efficiency 

 with which neutrality is preserved by carbonic 

 acid, without the actual discussion of a par- 

 ticular case. Let us therefore consider a solu- 



1 Henderson, "The Relation between the Strengths of 

 Acids and their Capacity to Preserve Neutrality," American 

 Journal of Physiology, XXI, 173, 1908. 



