150 



COLLOIDS IN BIOLOGY AND MEDICINE 



This table shows the remarkable fact that the first traces of salt 

 have a much greater influence than somewhat greater concentra- 

 tions. 0.01 normal Na 2 S04 added to salt-free albumin raises the 

 coagulation temperature about 6.4 C. while a similar addition to 

 albumin already containing 0.04 normal Na 2 SO 4 raises the coagula- 

 tion temperature only 0.6 C. We shall show the significance of this 

 fact later. 



If the salt is more concentrated, coagulation by heat varies; the 

 coagulation temperature rises continuously in the presence of K, Na 

 and NH 4 . Thus for 



3 normal KC1, coagulation occurs at 75 . 6 C. 

 3 normal NaCl, coagulation occurs at 73.6 C. 

 3 normal MgCl 2 , coagulation occurs at 75 . 4 C. 



The coagulation temperature reaches a maximum at a certain 

 salt concentration and then falls again in the case of other salts, 

 especially alkaline earths and the allied lithium. 



Maximum coagulation temperature, C. 



6 normal NH 4 C1 . , 72.8 



2 normal (NH 4 ) 2 SO 4 74.3 



1 normal LiCl 73.8 



0.5 normal CaCl 2 71 .4 



0.5 normal BaCl 2 72.2 



0.5 normal SrCl 2 72 



Some of the magnesium salts may completely inhibit heat coagu- 

 lation; MgCl 2 below 6 normal, Mg(NO 3 ) 2 below 4 normal. 



Cations also may be divided into different groups, according to 

 their influence: 



In the case of S0 4 , Cl, Br and N0 3 , there is a greater rise with 

 lower concentrations (up to 0.5 to about 1 normal) then a smaller 

 rise up to 1 normal. In the case of SCN and I the inhibition from 

 1 to 2 normal is so complete that no coagulation occurs even at the 

 highest concentration of the salt. In the case of citrate, acetate 

 and oxalate the coagulation temperature rises sharply from 0.05 to 

 0.1 normal, whereupon the curve again falls. Obviously this is as- 

 sociated with the strong hydrolytic cleavage of these weak acids in 



