74 PHYSICAL CHEMISTRY IN MEDICINE. 



metallic ion the precipitating power decreases in the 

 direction from fluoride toward bromide. No matter which 

 anion we take, therefore, we find that the cations always 

 follow the same order when arranged according to their 

 precipitating power, and, conversely, that with any cation 

 the anions always follow the same order when they are 

 arranged according to their precipitating power. This 

 law may also be stated thus: The precipitating power 

 of a salt is determined by the sum of the powers of its 

 individual ions, which act in large part independently 

 of each other. 



In what way, now, do the anions and the cations act ? 

 It might be thought, first of all, that both the metallic 

 and the acid ions of a salt have a specific precipitating 

 effect, and that the sum of these two positive values 

 constitutes the precipitating power of an electrolyte. 

 According to this conception, the precipitating power 

 of sodium acetate would be made up of the precipitating 

 effect of the sodium ion plus that of the acetic acid ion. 

 Many salts are known, however, which in spite of their 

 ready solubility precipitate protein in no concentration, 

 so that the above explanation does not hold at all in 

 these cases. Ammonium acetate, for example, does not 

 precipitate protein in any concentration, while the acetic 

 acid ion of sodium acetate and the ammonium ion of 

 ammonium sulphate are both strong precipitants. An 

 explanation without contradictions is offered by the fol- 

 lowing experimentally supported conception. Only the 

 metallic ions, or cations, act as the precipitating constituents 

 of the salts, and the oppositely charged anions inhibit 

 this precipitating property. 

 It is self-evident that only those salts will precipitate 



