Physiology. — “A method for the determination of the ion con- 
centration in ultra filtrates and other protein free solutions”. 
By Dr. R. BRINKMAN and Miss E. van Dam. (Communicated 
by Prof. HAMBURGER). 
(Communicated at the meeting of October 25, 1919). 
A. Determination of the concentration of free calcium ions. 
With regard to the biological actions of salts the actions of ions 
claim the first consideration. It is therefore desirable that we have 
at our disposal a method by which the ion concentrations are 
measured. 
Up to this only the concentration of the free H'-ions have been 
measured directly; the concentrations of other, also physiologically 
important ions were not measured at all or determined only indirectly 
by calculation. 
The concentration chain method can be applied only with great difficulty to the 
physiologically important metals owing to the disturbances brought about by the 
liberation of gas. Drucker !) has offered a method in which Ba-amalgam was used 
as an electrode. An analogous method can perhaps be worked out for the alkali 
metals. Such determinations have, however, not been made as yet. 
As an example of a case where it is necessary to know the ion 
concentration, we can point to the state in which the calcium occurs 
in the blood. It occurs there namely in three forms: as Ca’ ion, 
as undissociated calcium salt (Ca (HCO,),) and as colloidal caleium- 
protein compound. More or less 25 °/, of the total quantity of cal- 
cium occurs in the latter state. According to Rona and TAKAHAsHI *) 
the ion concentration of the calcium in the serum is determined by 
the equation 
[Ca ].[HCO,'] 
Nes) KonkanWaverase) 
[LH] 
For the serum which has the physiological [H-] and carbonic 
acid tension, this means a [Ca] of 20—25 mgr. per L. Of the 
more or less 100 mgr. per L. of calcium which occurs in the serum, 
therefore, only */, part is present in the ion form. We learn from 
1) Zeitschr. für Elektrochemie 19, 804 (1913). 
*) Biochem. Zeitschr. 49 p. 390. 
