268 LIME AND MILK. 



or real degree of acidity, that is the concentration of hvch^ogen 

 ions. The latter has been fixed by electrical methods, the value 

 found varies between o'i4 and 0*32 x 10-6 normal. For non,- 

 coagulating milk o-i6 and 0*22 x 10-6 normal hydrogen was found. 

 Therefore a deficiency in hydrogen ions could not be the cause 

 of failure to coagulate. 



These measurements made it possible to investigate in what way 

 the curdling time depends on the acidity of the milk. The curdling 

 time is inversely proportionate to the concentration of hydrogen 

 ions. With this result it was possible again to find in which 

 way the curdling time is influenced by the soluble lime salts. It 

 was shown, however, with great probability that the soluble 

 lime salts have very little influence on the rapidity of coagulation. 

 The experiments seem to show that the lime bound to casein is 

 the dominating factor in coagulation. 



This conception is entirely at variance with the accepted tenet 

 that the soluble lime salts exert an accelerating influence, and 

 necessitates a careful investigation of the argument always brought 

 for the hypothesis. 



It was found that : — 



1. When chlorate of lime is added to milk only about 50% 



of the added salt remains in solution, irrespective of the 

 concentration of the solution. For high concentration 

 (above 2%) no more lime ions are fixed in non filtrable 

 form. That all the same at this percentage the chlorate 

 of lime acts acceleratorily, may be explained in this 

 way, that the adding of this salt materiall}" increases the 

 number of hydrogen ions. 



2. The dissociation of the lime salts in milk is very limited, 



certainly less than 12%. 



3. The adding of soluble oxalate does not (as generally 



supposed) precipitate in the first place the dissolved 

 lime salts, but the pseudo-dissolved lime salts. In 

 milk containing 50 milligrams CaO (monoxide of calcium) 

 per 100 cubic centimeters serum, 12 milligrams CaO 

 was precipitated when the equivalent quantity of oxalate 

 of potash was added. This milk refused to curdle. 

 But by means of a chlorate of lime solution it could 

 be regenerated in spite of the fact that the quantity 

 of normally dissolved lime salts hardly increased (40 

 instead of 39 milligrams per 100 cubic centimeters of 

 serum). 



4. That soluble citrates retard or destroy curdling is always 



explained through precipitation of lime salts, citrate 

 of lime does not dissolve easily- But the experiment 

 shows something else. When soluble citrates are added, 

 the " colloidal " lime salts dissolve normally. The 

 percentage of dissolved lime salts increases considerably 

 and yet the milk declines to coagulate. Further, it 

 is found that citrate of potash wall solve part of the lime 

 bound to casein and ^his fact is in accord with the new 

 conception. 



