Summary of tbe Results. 



1. Definition. The tension of carbonic acid in natural 

 waters is the percentage of the gas in air being at ordinary 

 pressure in diffusion-equilibrium with the water. It is deter- 

 mined simply by shaking a sample of the water with a little 

 air and determining by analysis the percentage of carbonic 

 acid in the latter. 



2. Theoretical. The carbonic acid is present in natural 

 waters chiefly in combination with carbonates and forming 

 dissociable bicarbonates. At low tensions the relation between 

 the tension and the quantity of the gas corresponds exactly to 

 the formula 



— = Constant. 



X 



Hence it follows that the equilibrium is expressed by the 

 formula 



RCO., + H._ CO., -^ RH., C._ 0, 



and that the bicarbonates present are those of alkaline earths, 

 chiefly lime (pp. 357 — 62). 



3. Tension and temperature. The tension varies with 

 the temperature inversely as the absorption-coeft'icient of the 

 water (determined on p. 356) and besides it rises a little with 

 rising temperature owing to increased dissociation (pp. 363—66). 



4. Basaltic rocks absorb carbonic acid and are trans- 

 formed into carbonates. They are capable of reducing the CO»- 



