viscometrv 



less when the particle is oriented parallel to the direction of flow than 

 when it is randomly oriented. The situation with respect to flattened 

 ellipsoids is similar, for Peterlin (19) has shown that the intrinsic 

 viscosity of oriented plates is very little different from that of spheres. 

 The equations derived by Simha are potentially very useful, 

 for they make it possible to interpret the intrinsic viscosity of a suspen- 

 sion of rigid particles in terms of the ratio of length to thickness of the 

 particles. It is necessary, however, to have some independent means 

 of deciding whether the particles resemble rodlike or platelike ellipsoids 

 of revolution. The Simha equation, particularly the one for rods, is 

 rather cumbersome in the form presented. Mehl, Oncley, and Simha 

 (17) have calculated values of intrinsic viscosity which correspond to 

 various values of the axial ratio, h/a., for both rodlike and disklike 

 particles. These values are reproduced in Table II. Through the 

 use of this table, the determination of axial ratios from viscosity 

 measurements is greatly simplified. 



Table II 

 Intrinsic Viscosity of Ellipsoids of Revolution (17) 



The question of paramount importance is whether or not these 

 theoretical equations of Simha are actually valid. Mehl et al. at- 

 tempted to arrive at an answer to the question by comparing the 

 shapes calculated from viscosity data for numerous proteins with those 

 calculated from difl'usion and sedimentation data, on the assumption 

 that the protein particles are {a) elongated ellipsoids of revolution and 

 {b) flattened ellipsoids of revolution. The shapes were calculated 

 from sedimentation and difl'usion data by the following method. 



