ON PHYSICO-CHEMICAL METHODS AND PROBLEMS. 13 



of the base common to all of them. If the salts are 

 arranged according to their bases, then they follow each 

 other in a certain order which is independent of the 

 acid common to all. 



The effect of a salt upon the coagulation temperature 

 is therefore made up of two components the effect of 

 the acid and the effect of the basic parts. We call this an 

 additive ion effect. 



The remarkable phenomena observed when two salts 

 Si and 52 together affect the coagulation-point give us 

 a deeper insight into the important biological relations 

 existing between proteins and salts. 



If in a protein-salt mixture to which a definite amount 

 of 52 has been added we allow the salt Si to vary in 

 concentration, while in a second series of experiments 

 we repeat this but use a different amount of S2, etc., we 

 obtain a group of curves. A second series of curves 

 are obtained by using constant amounts of Si and varying 

 amounts of S2. In this way we obtain two groups of 

 curves which illustrate very well the mutual effects 

 of two salts upon protein coagulation. These curves 

 show in a very remarkable way points at which they 

 cross each other, in other words a constancy in the 

 coagulation-point as soon as certain quantitative rela- 

 tions exist between the two salts. When this is attained 

 a change in the concentration of one of the salts which 

 at other times would bring about a change in the coagu- 

 lation temperature remains entirely without effect even 

 when the amount of the change is four or five times as 

 great; 



A point at which the curves cut each other may be 

 shown also between the combination curve 



