LAWS OF ELECTROLYTIC DISSOCIATION 85 



used and is rendered slightly alkaline with NaHCOs, a clear stable 

 supersaturated lime solution is obtained. Dialysis experiments have 

 demonstrated that the greater portion of the Ca in serum is present 

 in a dialysable form. This excludes the possibility that the excess 

 of calcium in the serum could be present in the form of a colloidal 

 suspension or as a solution of a carbonate or phosphate. That 

 portion of the calcium which in the compensation dialysis experi- 

 ments was found to be non-diffusible is but a small fraction of the 

 excess calcium present, and this portion only may be regarded as 

 combined in an undissociated calcium-protein compound. 



Brinkman and van Dam,"*^ using another method, confirmed the 

 solubility data of Rona and Takahashi (22 mg. Ca++ per liter, for 

 [H+] = 3 X 10-8 and 20°), and they also found 22 mg. Ca++ ions 

 in the ultrafiltrate of blood serum at [H+] = 3 X 10-^. In the 

 serum itself, in those few cases in which their method could be ap- 

 plied, they found the same amount of Ca++ ions. If Rona's com- 

 pensation dialysate and Brinkman's ultrafiltrate be regarded as 

 being to a certain degree the same, then all of these results may be 

 explained only on the following assumption. The ionized calcium 

 is present in the serum in a concentration within the limit of its 

 actual solubility and not in a supersaturated state, and that the 

 excess calcium is present but to a small extent as a protein complex 

 and largely in true solution in an undissociated form of unknown 

 nature. 



The following further comment is to be made upon these investi- 

 gations. In the first place Rona's as well as Brinkman's solubility 

 determinations apply to a temperature of 20°. Secondly they 

 assume the [H+] in blood to be 3 X 10~^ whereas for 38° it should 

 be taken as 4.5 X 10"^. Thirdly, it must be pointed out that the 

 theory of activity, which is to be discussed in the next chapter, 

 could not yet have been taken into consideration, and it is prob- 

 able that the factor of 0.9 (see footnote on page 84) is too low. 



*5 R. Brinkman and E. van Dam. Kon. Akad. Wet. Amsterdam 22, 762 

 (1920). The method used by these authors for the determination of Ca''"''' 

 ions consisted of establishing the amount of oxalate to be added to a solution 

 containing calcium in order just to exceed the limit of solubility of the calcium 

 oxalate produced. Since the solubility product [Ca"'"''] X [oxalate ~] is con- 

 stant (0.055 millimols per liter at 20°) it is possible from the above amount 

 of the added alkali oxalate to calculate the Ca''"'' present. All the other 

 methods of estimating calcium determine the total calcium. 



