• IS: 1206 (Part 3)1978.


  • Kinematic viscosity is defined as the quotient of the absolute or dynamic viscosity divided by the density of the liquid both at the same temperature.


  • B S U — Tube Modified Reverse Flow Viscometer
  • The viscometer shall be made of clear borosilicate or other heat resistant glass free from visible defects.
  • A suitable bath for immersion of viscometer so that the liquid reservoir or top of the capillary whichever is uppermost is at least 2 cm below the upper bath level.
  • Provision shall be made for visibility of the viscometer and the thermometer.
  • The thermometer of capacity 90˚ C and with an accuracy of 0.10 C
  • Stopwatch capable of being read up to 0.5 seconds.

Calibration of Viscometer

  • Any liquid of known viscosity may be used for calibration of viscometer.
  • Charge the clean dry viscometer by pouring the known viscosity material.
  • Place the charged viscometer in the bath maintained at a temperature within 0.10 C.
  • Allow the charged viscometer to remain in the bath long enough to reach the main test temperature.
  • Measure to within 0.5 seconds the time required for the leading edge of the meniscus to pass from the first timing mark to the second.

C=       ——
V =Viscosity in centistokes for the standard liquid

t  =Efflux time in seconds.

  • If the visco meter is used at a location other than the calibrating laboratory the constant ‘C’ should be corrected for the difference in the acceleration of gravity ‘g’ at the two locations as follows


C2 =   ——- xC1

C2 = Calibration constant in the testing laboratory
C1 = Calibration constant in the calibration laboratory
g2 = acceleration of gravity at the testing laboratory
g1 = acceleration of gravity at the calibrator laboratory


  • Mount the BS U – Tube viscometer in the constant temperature bath keeping tube L vertical.
  • Pour sample through tube N to a point just above filling mark 0.
  • Allow the sample to flow freely through capillary R, taking care that the liquid column remains unbroken until the lower mark H and then arrest its flow by closing the timing tube with a cork or rubber stopper in tube L.
  • Add more liquid, if necessary to bring the upper meniscus slightly above mark 0.
  • After allowing the sample to attain bath temperature and any air bubble to rise to the surface (Usually, about 20 to 30 mm is required), gently loosen the stopper allowing the sample to flow until it is approximately at the lower filling mark H and press back the stopper to arrest flow.
  • Remove the excess sample above filling mark 0 by inserting the special pipette until its cork rests on top of the tube N and apply gentle suction until the air is drawn through
  • The upper meniscus shall coincide with mark 0.
  • Allow the viscometer to remain in the constant temperature bath for a sufficient time to ensure that the sample reaches temperature equilibrium.
  • It takes about 20 min at 38°C, 25 mm at 100°C and 30 miii at 135°C.
  • Remove the stopper in the tube N and L respectively and allow the sample to flow by gravity.
  • Measure to the nearest 0.1 seconds the time required for the leading edge of the meniscus to pass from timing mark E to the tinting mark F.
  • If this efflux time is less than 60s, select a viscometer of smaller capillary diameter and repeat the operation.

                 Kinematics viscosity, cSt = C x
C = Calibration constant of the viscometer in centistokes per second

t  = Efflux time in seconds.


  • Report always the test temperature along with the results.


The duplicate test results should not differ by more than the values given below

Material Repeatability Reproducibility
Asphaltic bitumen at 135°C 1.80% of mean 8.80% of mean
Cutback bitumen at 60°C
Below 3000 cSt 1.50% of mean 3.00% of mean
3000 to 6000 cSt 2.00% of mean 9.90% of mean
Above 6000 cSt 8.90% of mean 10% of mean


  • After completion of the test clean the viscorneter thoroughly by mixing with an appropriate solvent completely miscible with the sample followed by a completely volatile solvent.
  • Dry the tube bypassing slow stream of filtered thy air through the capillary until the last trace of solvent is removed.

1206 (Part 3) 1978

Description Time taken in seconds Viscometer

in Cst

Remarks :

Viscosity – Excel Performa


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