COBALT CHLORIDE. 



151 



VISCOSITY MEASUREMENTS. 



dx 

 It can be shown that the rate , at which the angular distortion of a portion 



U(/ 



of fluid changes, is proportional to the shearing stress upon the portion of the 



ii i* 



fluid. This ratio, shearing stress () divided by --, for a given fluid, is called 



at 



its coefficient of viscosity. It may be written thus, 



dt 



in which rj is the coefficient of viscosity. 



Percentage of Acetone 



FIG. 70. CONDUCTIVITY OF COBALT CHLORIDE IN MIXTURES 

 OF ACETONE AND METHYL ALCOHOL AT 0. 



The viscosity of fluids is often determined by the methods of Poisseuille and 

 of Hagenbach. The viscosity is calculated by the formula * 



/* = 



8vl 



where P is the actual pressure, diminished by that pressure which would be 

 necessary to give to the fluid, while flowing through capillary tubes, the 



1 Hagenbach : Pogg. Ann., 19, 385 (1860). 



