1903-4.] Note on the Standard of Relative Viscosity , etc. 227 
Note on the Standard of Relative Viscosity, and on 
“ Negative Viscosity.” By W. W. Taylor, M.A., D.Sc. 
Communicated by Professor Crum Brown. 
(Read March 21, 1904.) 
The Unit of Relative Viscosity. 
The absolute viscosity calculated from the formula 
irprH 
(where jo = the pressure, t the time, r the radius, l the length of 
capillary, and v the volume of liquid), which connects the viscosity 
of a liquid with the rate of flow through a long capillary tube, is not 
often made use of, mainly on account of the difficulty of accurately 
determining some of the constants ( r in particular). Further, a 
correction has to be made if the velocity of outflow is not sufficiently 
slow.* For most purposes the viscosity is referred to that of a 
given liquid as standard, and is calculated from the formula 
st 
Vo 
where r) 0 , s 0 , ^ 0 , are the viscosity, density, and time of flow through 
a tube of a given volume of the standard liquid, and rj, s, t are the 
corresponding data for the other liquid. Of tj 0 , Ostwald-Luther 
(. Phys . Chem. Messungen , p. 260) say, “ the viscosity of water at 0° C. 
(or at the temperature of experiment) is put = 1.” 
It is the general practice to take the viscosity of the solvent 
(whether water or other liquid) at the temperature of experiment 
as rj 0 = 1 . In place of this, it would be an advantage if the 
viscosity of water at 0° C. were taken as standard, and the relative 
viscosity of liquids and solutions referred to this alone. 
For certain purposes, e.g. demonstration of the additive 
character of the viscosity of salt solutions, the relation between 
viscosity and atomic weight, or between viscosity and concentra- 
* Cf. Ostwald-Luther, Phys. Chem. Messungen , p. 359. 
