\. 
1907-8.] On the “ Negative” Viscosity of Aqueous Solutions. 469 
the cations. In particular, the values for tetra-ethyl ammonium chloride 
and bromide lie very close together, much more so than the viscosities of 
hydrochloric acid and hydrobromic acid, of the potassium salts, or of the 
ammonium salts. From this it would appear that the viscosity of salt 
solutions cannot be regarded as simply an additive property. 
The data are insufficient to enable one to make an effective comparison 
of the effect on rj of the change from methyl to ethyl to propyl, but the 
following approximate figures are of some interest. They are for '5 molar 
solutions at 25° C. ; the value for ammonium iodide is taken from Getman’s 
tables, for tetra-methyl ammonium iodide by extrapolation, and for tetra- 
propyl ammonium iodide and tetra-ethyl ammonium bromide by inter- 
polation from the curves in fig. 1. 
*5 m. NH 4 I t) = "00858 
(CH 3 ) 4 NI -00920 ' 
(C 2 H 5 ) 4 NBr -01052 
(C 3 H 7 ) 4 NI -01294 
cliff. -00062 
•00132 
•00242 
