49928 str (100)

So    GRAP HIC AL METHODS

plotting of V/ttR³ against PR/₂L gives a w cun^re, independent of R. For many rheologists, who find the above mathematical tr ment difficult, such graphical methods are i|| helpful. He also shows how account can be tak^ of the discrepancies of phenomena of the HyiJ¹ which, it must not be forgotten, can occur in rectilinear systems, though it is not so easy to observe them. The author is not aware of anv instances in the literaturę on this subject; but he has obseryed a somewhat similar phenomenon for certain types of cream.

Schofield goes on to show how the velocity gradient at the wali of the tubę can be deduced from experimental figures for V, P and R, and points out the peculiar advantages of the generalised form of the eąuation

(_n _j_

Yelocity gradient = -    —,

where n = d(log V)/d{log P), in dealing with Ostwald systems.

BIBLIOGRAPHY

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4°9-

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139; 193*, Sfij ^I4^I*