SALTS 447 



of salt solutions, where excellent lyotropic series result, and pH 

 cannot possibly be a factor; thus, the surface tension of salts gives 

 the following definite lyotropic series: Fl > CI > Br > I, SCN. 



If the situation is viewed as physiologists would see it, it would 

 be necessary to grant, on the basis of Loeb's contention, that the 

 effect of ions is not specific but depends solely on electrostatic 

 properties such as valence and sign and magnitude of charge; 

 in this case, a plant or an animal should be indifferent to the ion 

 it receives just so long as it is of the proper valence and charge. 

 Were this true, then our entire story of ion nutrition would 

 collapse. Any monovalent ion or any bivalent ion would do, 

 which we have already seen is not true. A plant needs potassium 

 and will have little or nothing to do with sodium, while an 

 animal demands sodium, and potassium will not do as a sub- 

 stitute. (The heavy metals, which in any but the smallest quanti- 

 ties are highly toxic, Loeb excepted. They and hydrogen do 

 not come into the valence rule.) Northrop summarizes the 

 valence rule as apphed to physiological and similar organic 

 reactions, as follows: There is no doubt that any individual 

 effect of ions of the same valence — except for hydrogen and heavy 

 metals — is so small in comparison with the pure valence effect 

 as to be entirely negligible. If precautions in regard to acidity 

 are taken, a great many of the Hofmeister series disappear. How- 

 ever, a general statement cannot be made to cover all types of 

 experiments. In concentrated salt solutions and in respect to 

 other properties or other experiments, there is very hkely a definite 

 characteristic ion effect. (Loeb's experiments were limited to 

 fairly dilute salt solutions.) This conclusion deserves serious 

 consideration and undoubtedly holds for metal suspensions — 

 where the effect of ions is in direct relation to valence and electric 

 charge, though not in direct proportion, as tri- and quatravalent 

 ions are more than three and four times as effective as monovalent 

 ones. However such a conclusion is not generally held in regard 

 to protein solutions of which the Hofmeister series (with pH 

 control) are very characteristic. 



That Hofmeister, or lyotropic, series are more characteristic 

 of protein than of metal suspensions is due to the fact that 

 hydration is a greater factor in the former. Kruyt states that 

 lyotropy is an expression of hydration, pure and simple, of the 

 orientation of water dipoles, which explains why, in proteins, the 



