The term “slippage” was introduced by Bingham and Green to account for the flow of plastic or pseudoplastic materials when the shearing stress falls below the yield value as defined by them. The idea of slippage was given mathematical expression by Buckingham in his equation for plastic flow in capillary tubes as shown in Equation 1S = μ (F − 4/3f + f43F3) + ceFr(1) whereS= rate of shear,4π Vtr3;F= shearing stress,Prg2l;f= yield value; μ = mobility;c= slippage constant;e= thickness of liquid layer causing slippage. This equation has been recognized by a considerable following as representing the facts of flow in capillary tubes for all materials which do not give straight‐line flow‐pressure curves. But very few workers have made any attempt to test the equation over a wide range of conditions.