Tables 149-lSl. 



VISCOSITY. 

 TABLE 149. — Viscosity of Fluids and Solids. 



155 



The coefBcient of viscosity of a substance is the tangential force required to move a unit area of a plane surface 

 with unit si -ed relative to another parallel plane surface from which it is separated by a layer a unit thick of the sub- 

 stance. Viscosity measures the temporary rigidity it gives to the substance. The viscosity of fluids is generally meas- 

 ursd by the rate of flow of the fluid through a capillary tube the length of which is great ia comparison with its diameter. 

 The equation generally used is 



H, the viscosity, = — ^ I « — ' ■ 



I28<2tf+X) 





where 7 is the density k/cm'), d and / are the diameter and length in cm of the tube, Q the volume in cm' discharged 

 in t sec., X the Couette correction which corrects the measured to the effective length of the tube, h the average head 

 in cm, m the coefBcient of kinetic energy correction, rmP-lg, necessary for the loss of energy due to turbulent in distinc- 

 tion from viscous flow, % being the acceleration of gravity (cm/sec/sec), v the mean velocity in cm per sec. (See Tech- 

 nologic Paper of the Bureau of Standards, 100 and 112, Herschel, igiy-igiS, for discussion of this correction and X.) 



The fluidity is the reciprocal of the absolute viscosity. The kinetic viscosity is the absolute viscosity divided by 

 the density. Specific viscosity is the viscosity relative to that of some standard substance, generaUy water, at some 

 definite temperature. The dimensions of viscosity are ML'^T'^. It is generally expressed in cgs units as dyne-seconds 

 per cm* or poises. 



The viscosity of solids may be measured in relative terms by the damping of the oscillations of suspended wires 

 (see Table 78). Ladenburg (igo6) gives the viscosity of Venice turpentine at 18.3° as 1300 poises; Trouton and 

 Andrews (1904) of pitch at 0°, 51 X lo^", at 15°, 1.3 X lo*"; of shoeiuaJieis' wax at 8°, 4.7 X io«; of soda glass at 575°, 

 II X 10^; Deeley (1908) of glacier ice as 12 X \^\ 



TABLE 150. — Viscosity of Water in Centipoises. Temperature Variation- 



Bingham and Jackson, Bulletin Bureau of Standards, 14, 75, 191 7. 



TABLE 151. — Viscosity of Alcohol-water Mixtures in Centipoises. Temperature Variation. 



Smithsonian Tables. 



Same authority as preceding table. 



