86 HYDROGEN ION CONCENTRATION 



These three conditions all point in the direction of the probability 

 that the solubility of calcium as determined in these experiments 

 is too low. It is possible that the discrepancy between the solubility 

 of calcium in plasma as based on theory and its actual calcium 

 content is not as great as these investigations appear to indicate. 



It may be seen from the above example how much more important 

 the exact knowledge of natural constants is than hypotheses are 

 for the clear conception of physiological facts. It is surprising that 

 such physiologically important constants have not yet been deter- 

 mined. The theories of formation of calculi and of the deposition 

 of lime in the blood vessels are truly phantastic, as long as it is not 

 established whether or not the calcium of the blood is at all in a 

 supersaturated state. 



How complicated the previously discussed problem of uric acid 

 is may be appreciated at this juncture, when it is recalled that in 

 this case the slight solubility of the free acid is combined with the 

 slight solubility of its Na-salt. The preceding chapter concerned 

 itself with a slightly soluble acid whose salts are easily soluble 

 (benzoic acid), while the present chapter deals with slightly soluble 

 salts whose components (CO2, Ca(H0)2) are more soluble than the 

 salt. In the case of uric acid we have a condition not yet theoreti- 

 cally investigated, where both the free acid and its salts are but 

 slightly soluble. 



23. The relation of the hydrion concentration to the solubility of a 



slightly soluble ampholjrte 



If the partial solubility of the slightly soluble ampholyte be = 

 X, then the total solubility is 



A = X + A+ + A- 



where A+ and A~ denote the ampholyte in its cationic and anionic 

 forms respectively. 



The experimental investigations apply here insofar as the solu- 

 bility minimum has been studied. This condition obtains when 

 [A+] + [A""] is at a minimum, therefore, at the isoelectric point. 

 Thus we return to the consideration fully discussed previously on 

 page 70. 



Finally it must be recalled once more that all of this discussion 



