CHAPTER XI 

 THE ELECTROCHEMISTRY OF COAGULATION 



1. The Coagulation of the Casemates by Alcohol. — If one- 

 half a cubic centimeter of a 0.0125 N solution of KOH, neutralized 

 either to phenolphthalein or to litmus by the addition of casein, 

 be added to 10 cc, i.e., to 20 volumes of 99.8 per cent alcohol, 

 no coagulation of the protein occurs, although the solution which 

 is thus obtained is appreciably more opalescent than a solution 

 of equal concentration in water containing no alcohol. Even 

 if, instead of employing a solution of potassium caseinate in water, 

 we employ a 0.0125 N solution of KOH in 75 per cent alcohol, 

 containing 1.6 or 2.5 per cent of casein, adding | cc. of this to 

 10 volumes of 99.8 per cent alcohol, still no coagulation of the 

 caseinate occurs, although it is now dissolved or forms a stable 

 suspension in a 98.6 per cent solution of alcohol. The caseinate 

 can, however, be readily coagulated by adding to this mixture 

 an equal volume of ether and allowing it to stand for a few hours. 



Very different is the behavior of the caseinates of the alkaline 

 earths. If to 10 cc. each of 60, 70, 75 per cent, etc., solutions of 

 alcohol we add ^ cc. of a 0.012 N solution of Ca(0H)2, neutralized 

 to phenolphthalein by casein, distinct coagulation of the casein- 

 ates occurs, on shaking, when the final concentration of alcohol 

 in the mixture is about 55 per cent. The same is true for an 

 equally concentrated solution of barium hydroxide neutralized 

 to phenolphthalein by casein. For strontium caseinate the 

 limiting concentration of alcohol at which coagulation occurs is 

 much higher, about 70 per cent. In all cases coagulation is much 

 accelerated by energetic shaking of the mixture. 



It is of interest to compare the marked difference between the 

 behavior of the caseinates of the alkalies and of the alkaline earths 

 upon the addition of alcohol to their aqueous solutions, with the 

 numerous other differences which subsist between the caseinates 

 of the alkalies and those of the alkaline earths. 



Thus the aqueous solutions of the "neutral" or "basic" casein- 



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