226 PROTOPLASM 



stress required to produce it, as abscissas; the line OA is straight 

 and passes through the origin, which means that the ratio of 

 flow to force is a constant. The graphs OB and CD are those of 

 non-Newtonian Uquids; they are either curved or do not pass 

 through the origin ; the ratio of flow to force is a variable. Fluids 

 exhibiting anomalous flow behave as if they contained aggregates 

 which under stress are sheared apart, thus increasing the fluidity. 

 Forces that hold molecules together in aggregates may also cause 

 the material to show elasticity. For this reason, Freundlich 

 and Reiner both assumed that elasticity is responsible for the 

 deviation of flow from Poiseuille's law. Such a conclusion was 



shown to be justified from the 

 behavior of two soap solutions 

 the viscosity of which was 

 measured in a capillary vis- 

 cometer. One was found to 

 obey Poiseuille's formula, while 

 the other deviated from it; the 

 former should not show elastic 

 qualities, while the latter 

 "I ~ri ~ \ 7~ ,^ ,, , should. This proved to be 



Fiu. 110. — Graphs of true {OA) and ^ 



anomalous {OB and OC) viscous flow true. Furthermore, the elastic 



(ordinates are rate of flow; abscissas are possessed structural char- 



shearing stress). ^ '^ 



acteristics which permitted it to 

 hold a small metal particle in suspension though it was but twice 

 as viscous as water, while the soap solution which showed true 

 viscous flow would not support a similar particle even though four 

 hundred times as viscous as water. The structural features that 

 gave to the non-Newtonian soap its elasticity and rigidity were 

 probably responsible for its non-Newtonian behavior. All 

 typical lyophilic colloids which form jellies exhibit anomalous 

 flow, and all are elastic. The American school of rheologists are 

 inclined to dissent from this view, for they regard viscosity and 

 elasticity as independent variables. Evidence in their support 

 is the fact that certain other suspensions, such as pigments and 

 clays, also exhibit anomalous flow yet are presumably inelastic. 

 On the other hand, oils such as linseed, which when pure show 

 true viscous flow, on oxidation set to an elastic jelly. Perhaps 

 it must be granted that not all cases of anomalous flow are due 

 to those structural properties that are responsible for elasticity, 



