AbstractA two‐way capillary viscometer for measuring shear rates from1,000,000 sec.−1at pressure drops up to 1,000 lb./sq.in. has been designed. It consists of a capillary tube mounted vertically between two sample reservoirs, of which the lower one is connected to a mercury manometer. The driving force, gas under pressure in a large tank, is connected to the upper reservoir and the manometer, thus allowing the sample to be moved in either direction through the capillary. The special feature of this viscometer is the indirect automatic measurement of bulk velocity of the fluid sample (3 to 20 cc.) in the capillary tube by means of a mercury manometer.The precision of measurement of the velocity is one part in four hundred and can be maintained over the whole range of shear rates by the appropriate choice of the ratio of the diameter of the capillary and manometer tube.Energy losses due to capillary heating and kinetic energy are given in terms of ΔPacross the capillary. Couette end effect was found to be 0.3 diam.A study of the rheology of polyacrylonitrile (PAN) in concentration range of ½ to 10½% PAN shows that the non‐Newtonian behavior and elasticity of PAN solution increases rapidly with conce