If, on the other hand, carbonic acid is considered with lime instead of with oxygen, 

 the reason is that there is a much closer relation between carbonic acid and lime. (The 

 relations between carbonic acid and magnesium are similar but these combinations are 

 always present in only such negligible amounts that especial reference to them can be 

 omitted.) 



Calcium oxide functions as the regulator of carbonic acid economy and of the natural 

 reaction of the water . This Justifies a somewhat more explicit treatment of the subject. 



Carbonic acid is present in the water in three different forms, as a free gas or in 

 more or less combined forms, and everyone of these forms plays a vital role in the 

 metabolic cycle of the pond. 



Vfe distinguish I 



(1) Free, water soluble Carbonic acid (CO2). 



(2) Bicarbonate-carbon dioxide in combination with calcium bicarbonate 

 (Ca(HC03)2) which occurs in solution only. 



(3) Itonocarbonate carbon dioxide. It appears combined with calcium 

 carbonate (CaC03) which is soluble in only small amounts (13 milligrams, 

 corresponding to an A.C.C. of about 0.23) in carbon dioxide-free waters, 

 but which is never present in waters containing free carbon dioxide, 

 hence will normally be found — in caicentrated form — only at the 

 bottom of the pond and upon plants, as CaCO^« 



There exists a state of equilibrium in the ratio of carbon dioxide to calcium 

 carbonate, and whenever unilateral changes occur, there is a tendency toward re- 

 establishment of this equilibriim.. 



Tillmanns and Heublein (after Schaeperclaus, 1926) found that a certain calcium 

 bicarbonate rate (practically proportional to the A.C.C.) corresponds to a certain rate 

 of free carbon dioxide. In table 7, we have the figures as found by Tillmann and others. 



Table 7. 



State of equilibidura between bicarbonate-carbonic acid and carbon dioxide 

 at different rates of hydrochloric acid combination capacity (A.C.C.) and 

 the "normal" pH rate resulting therefrom. 



A.C.C. corresponding 



cc. n HCl calcium content carbon dioxide free carbon dioxide pH rate 



per liter mg.CaO per liter 



3.3-8.0 



8.22 

 8.10 

 7.97 

 1.83 

 7.69 

 7.56 

 7.-43 

 7.31 

 7.22 

 7.U 

 7.07 

 7.00 

 6.95 

 6.90 



5A 



