1903-4.] Note on the Standard of Relative Viscosity , etc. 229 
There is no need to determine t 0 directly ; the simplest way is 
to determine t for the solvent at the temperature of experiment, 
and to calculate t Q from it by means of the table of viscosity of 
water at various temperatures. 
“Negative Viscosity.” 
The bearing of this on “negative viscosity” (a term frequently 
used to denote that the viscosity of the solution is less than that 
of the solvent at the same temperature) is indicated below. 
In general, the temperature coefficient of the solution will be 
(a) less or ( b ) greater than that of the solvent. 
(a) If at a given temperature the viscosity of the solution is 
greater than that of the solvent, and its temperature coefficient is 
smaller than that of the solvent, at higher temperatures the 
viscosity-temperature curves will diverge, but at lower tempera- 
tures they will approach, and finally intersect at some temperature, 
below which “ transition temperature ” the solution will exhibit 
“negative viscosity.” 
(b) If, on the other hand, the temperature coefficient of the 
solution be greater than that of the solvent, the curves will 
diverge on lowering the temperature, whilst they will approach 
and intersect on raising the temperature. In this case the 
solution will exhibit “ negative viscosity ” at higher temperatures. 
The particular case where the solution and solvent have the 
same temperature coefficient needs no discussion. 
Aqueous solutions of electrolytes appear to belong to group (a), 
and in some cases, at any rate, a solution has “ positive viscosity ” 
at one temperature and “negative viscosity ” at lower temperatures, 
e.g. KC1, KN0 3 ,* etc. 
Until quite recently no solutions other than aqueous solutions 
of electrolytes were known to exhibit “negative viscosity,” and 
on this Euler f based his explanation, — “the electric charge of the 
ion causes a compression (electro- striction) of the water, on 
account of which the viscosity is diminished.” But Miihlenbein, \ 
* Sprung, Pogg. Ann., 159, p. 20 (1876). t Loc. cit., p. 541. 
+ Dissertation, Leipzig, 1901. Also Wagner, Zeit. f. Phys. Chem., 46, 
p. 872 (1903). 
