319 



For very viscous materials, measurements of viscosity are made by noting 

 the rate of elongation of fibers under load or by observing the aperiodic motion 

 of an elastic system displaced from its position of equilibrium and damped by 

 the viscous material. 



The formula for the rate of elongation of fibers as employed by H. R. 



Lillie 110 is 



Lxgxk 

 rj, the viscosity, = -= — p„„ > 



where R is the radius in cm of the fiber of effective length, L (cm), g the 

 mass in grams of the attached load, k the acceleration of gravity (cm/sec 2 ), 

 and E the rate of elongation in cm/sec. 



For the aperiodic motion of the system consisting of the suspended inner 

 cylinder of Margule's apparatus described above, the formula is 



Ro 2 — Ri 



Kitz-ti) log e 

 the viscosity, = *? — 



4rrL log 10 ~ 



( RS-RS \ 



where t 2 and t 1 denote the times in seconds of angular positions 9 2 and 9 1 of the 

 suspended system from its position of equilibrium. The other characters have 

 the same significance as in the formula above for the rotating cylinder method 

 of measuring viscosity. (For reference, see footnote 108.) 



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

 of the oscillations of suspended wires (see Table 323). Ladenburg (1906) 

 gives the viscosity of Venice turpentine at 18.3° as 1300 poises; Trouton and 

 Andrews (1904) of pitch at 0°, 51xl0 10 , at 15°, 1.3 xlO 10 ; of shoemaker's 

 waxat8°,4.7xlO fi ;of soda glass at 575°, 11 x 10 12 ; Deeley (1908) of glacier 

 ice as 12 x 10 13 . 



Lillie, H. R., Journ. Amer. Cer. Soc, vol. 14, p. 502, 1931. 



TABLE 311.— VISCOSITY OF WATER IN CENTIPOISES 



(Temperature variation) 

 Part 1. — Low temperature 



(continn-ed) 



SMITHSONIAN PHYSICAL TABLES 



