547 



Through iiilerpolatioii it is found that 11 or 12 7o "f ""' ''^•^'I'^'si'ed 

 calcium corresponds to 0.0033 N ; 5 or 5'/, "/„ to 0.0019 N citrate, 

 and 3 7o 'o 0.0010 N citrate; iience that the activity is reduced 

 resp. to '/i6> Vjo Vso of its value through the substilution in the 

 unciianged citric acid. 



These values show good agreement with the results of the rennet 

 coagulation experiments, where 7i9> Viou» Viou ^^^ found. In view 

 of the uncertainty in the determinations with small quantities of 

 complex formation no better agreement can be desired. 



We may slill point out that also barium and strontium salts are 

 deprived of their free ions by addition of citrate. Thus 1 found in 

 diluted solutions of barium nitrate, strontium niliate and calcium 

 sulphate, which reqniied resp 



barinm strontium calcium 



23.0 cm' 25.4 cm' 25.4 cm' 



of titration liquid, that — when these 100 cm' contained '/luu resp. 

 Vso N sodium citrate — they consumed only: 



'/,„ N 21.6 cm' 6.0 cm' 11.2 cm' 



7.„ N 16.85 cm' 1.85 cm' 3.9 cm' 



3. Conclusion. 



a. The biological citrate action rests on the diminution of the 

 concentration of the free calcium ions throngh formation of complex 

 compounds or ions. This citrate action can also be shown in less 

 complicated systems than biochemical ones, e.g. in the solubility of cal- 

 cium oleate in citrate. 



h. Substituted citrates show there exactly the same diminution of 

 activity as has been observed in a biochemical reaction (as the 

 rennet coagulation). When either the alcohol group, or one of the 

 carboxyl groups is removed, the activity is reduced to 7i8 of its 

 value; this diminution is much greater wiien two groups are removed 

 at the same time. 



c. Citric acid owes its strong activity to the fact that it is a 

 multi-basic oxy-acid. 



Experiments with other ranlti-basic oxy-acids are in progress. I 

 refer for the literature to the extensive German publication, which 

 will shortly appear. 



36* 



