VISCOSITY. 



21 



some cases to have greater, and in other cases less viscosity than the original 

 solution. 



To explain this "negative viscosity" shown by certain salts in their power 

 to lower the viscosity of pure water, Euler employed the " electrostriction 

 theory" proposed by Drude and Nernst. 1 According to this theory the ion 

 is surrounded by a strong electrical field, in virtue of its charge, which causes 

 a strong compression of the liquid in this field. Euler holds that the effect 

 of a salt on viscosity is the result of two tendencies : First, that of the atoms 

 tending to increase the viscosity in inverse proportion to their migration 

 velocities; and second, the electrostriction tending to lessen the viscosity. 



Euler has calculated viscosity constants for a large number of ions, and 

 finds the relation between them and the migration velocities to be expressed 

 by the formula 



(A - 0.68) . C7(or (K - 0.68) . F) = a constant, 



where A and K are the viscosity constants and U and V are the migration 

 velocities of the anion and cation, respectively. Hydrogen and hydroxyl 

 ions are exceptions. Some of the values are given in table 5. 



TABLE 5. 



Wagner 2 has shown that Mullenbein's 3 measurements have discounted 

 Euler's explanation of negative viscosity, since the viscosity of the solvent 

 may be lowered by the addition of certain non-electrolytes, even when the 

 viscosity of the dissolved substance is higher than that of the solvent. With 

 ethyl alcohol, o-nitrotoluene gives an inversion-point, m-nitrotoluene a mini- 

 mum and p-nitrotoluene a maximum. 



He proposes, as an explanation, that the solute diminishes the quantity 

 of the solvent in a given space, and this leads to a diminution of the viscosity, 

 which diminution is partly compensated, however, by the solute itself. Ac- 

 cording to the relative magnitude of the various factors, the viscosity may 

 be increased or diminished. 



Dunstan 4 has investigated a large number of mixtures. He believes that 

 the increase in viscosity is due to the formation of loosely held complexes. 



1 Ztschr. phys. Chem., 16, 79 (1894). 4 Journ. Chem. Soc., 85, 817 (1904). Ztschr. 



2 Ibid., 46, 867 (1903). phys. Chem., 49, 590 (1904). 



3 Dissertation, Leipzig, 1901. 



