84 



HYDROGEN ION CONCENTRATION 



ions present in tiie solution, regardless whether these later are de- 

 rived from the solid phase or are added to the solution extraneously 

 as NaHCOs. Analogously to the assumption of certain approxima- 

 tions in the first part of this book, we may assume the concentra- 

 tion of the bicarbonate ions as being equal to that of the total 

 bicarbonate in solution. Furthermore it can be shown by means 

 of a solubility determination in a strongly alkaline reaction that 

 X is no longer analytically measurable and that practically X = 0. 

 The above equation is, therefore, simplified to the form 



A = K 



[H^ 



[HCO3 



The following values were found for A at 18°: 



Therefore, at 18' 



A = 342 X 



[HCOs- 



mols per liter 



For the conditions existing in the blood plasma, where [H+] 

 = 3 X 10-8 and [HCO3-] = 0.02 N, a solubility of 0.022 g. Ca++ 

 or 0.0294 g. CaO per liter is calculated. In reality one finds more 

 CaO in the plasma, at all events more than 0.1 g., and at times even 

 0.17 g. CaO per liter. In the whole blood there is about 0.1 g. 

 CaO per liter. It appears, therefore, that the plasma contains more 

 Ca than the amount corresponding to the solubility of CaCOa, and 

 it seems as if this were a case of a supersaturated solution. This 

 assumption is all the more plausible, since in practice it is quite easy 

 to prepare such supersaturated lime solutions, even in the absence 

 of protein. Thus, when instead of solid CaCOs a CaCl2 solution is 



* This is a correction factor which must be introduced in order to take 

 account of the fact that the active mass of the bicarbonate ions is somewhat 

 Bmaller than the concentration of the calcium bicarbonate. 



