92 PHYSICAL CHEMISTRY IN MEDICINE. 



of all a more intimate knowledge of the significance of 

 the ions for these changes in state. 



The neutral salts of ammonium, magnesium, and the 

 alkali metals are best adapted to such a study, as the pro- 

 tein precipitates produced by them can be reobtained in an 

 almost unaltered condition through dialysis of the salt. 

 The most important laws governing this reversible change 

 in state are the following: If the salts are arranged 

 according to their precipitating power, the acid ions (or 

 anions) always follow each other in the same order with 

 any given metallic ion, and, conversely, with any acid 

 ion the metallic ions (or cations) always follow each other 

 in the same order. The precipitating power of any 

 salt represents, therefore, the product of the effects of 

 its constituent ions, and the properties of these ions are 

 to a large extent independent of each other. 



A second law governs the character of the ionic effects. 

 It was found that the ions of a salt antagonize each other 

 in bringing about changes in the physical state of a colloid, 

 for the one ion has a precipitating action, while the other 

 has a solvent action, and, as the one or the other ion has 

 the upper hand, the salt under consideration either pre- 

 cipitates or prevents the precipitation of protein. The 

 effectiveness of ions is expressed in the following series: 



Cations arranged in the order of their precipitating 

 power. The most powerful comes first: sodium, potas- 

 sium, ammonium, magnesium. 



Anions arranged in the order in which they prevent 

 precipitation. The most powerful comes last: sulphate, 

 citrate, tartrate, acetate, chloride, nitrate, bromide, iodide, 

 sulphocyanate. 



To render what follows more intelligible it is necessary 



