Operation of Viscometer SOP

SOP for Ostwald Viscometer | SOP for Suspended-level Viscometer |

  • Viscometer SOP covers below points :
    • Definitions of Viscosity
    • Definitions of Dynamic viscosity
    • Definitions of kinematic viscosity
    • Operating procedure of Ostwald-type viscometer
    • Operating procedure of Suspended-level Viscometer
    • Viscosity Calculation formula
      • kinematic viscosity formula
      • Dynamic viscosity formula
    • Cleaning procedure of Viscometer
  • To lay down the procedure for cleaning and operation of Viscometer.
2.0 SCOPE :
  • The SOP is applicable for the cleaning and operation of Viscometer, used for measuring the viscosity of a fluid, the following viscometer are used in Quality Control Department.
Sr. No.Viscometer Type
01Ostwald-type viscometer, Size B
02Ostwald-type viscometer, Size F
03Suspended-level Viscometer, Size 1
04Suspended-level Viscometer,  Size 1A

  • Quality control Chemist and above
  • Quality Control Head

5.1 The determination of viscosity of Newtonian liquids is carried out by means of a capillary viscometer, unless otherwise specified, i.e., Methods A and B described below are recommended.

5.2 Definitions :

  • Viscosity :
    • It is defined as the resistance to flow.
    • At a molecular level, viscosity is a result of the interaction between the different molecules in the fluid i.e., friction between the molecule in the fluid.
    • Viscosity will determine the energy required to make a fluid flow.
  • Dynamic  viscosity :
    • It is defined as resistance to shearing flows, where adjacent layers move parallel to each other with different speeds. 
  • Kinematic viscosity :
    • It is defined as ratio of dynamic viscosity to density of that fluid.

5.3 Operation :

  • Method A : Using Ostwald-type viscometer
Ostwald-type viscometer
  • Fill the viscometer, previously washed and completely dried, with the liquid under examination through tube L to slightly above the mark G; using a long pipette to minimise wetting the tube above the mark.
  • Hold the tube vertically in a water-bath maintained at the temperature indicated in the monograph and allow to stand for not less than 30 minutes to allow the temperature to reach equilibrium.
  • Adjust the volume of the liquid so that the bottom of meniscus settles at the mark G.
  • Suck or blow the liquid to a point about 5 mm above the mark E.
  • After releasing pressure or suction, measure the time taken for the bottom of the meniscus to fall from the top edge of mark E to the top edge of mark F.
  • Method B : Using the Suspended-level Viscometer
Suspended-level Viscometer
  • Fill the viscometer through tube L with a sufficient quantity of the liquid under examination to ensure that bulb A is satisfactorily filled without blocking the ventilation tube M.
  • After the tube has been placed vertically in a bath maintained at the specified temperature allow it to stand for not less than 30 minutes to allow the temperature to reach equilibrium.
  • Close tube M and apply suction to tube N until the liquid reaches a level about 5mm above mark E.
  • Hold the liquid at this level by closing tube N and open tube M.
  • When the liquid is clear of the capillary end of tube N and the lower end of tube M, open tube N.
  • Measure the time taken, to the nearest 0.2 of a second, for the bottom of the meniscus to fall from the top edge of mark E to the top edge of mark F.
  • If the end of tube M becomes blocked by the liquid at any time while the flow time is being measured, the determination must be repeated.
  • The result is not valid unless two consecutive readings do not differ by more than 1 %.
  • The average of not fewer than three readings gives the flow time of the liquid under examination.

5.4 Calculation :

  • kinematic viscosity (v):
    • v =Kt
    • Unit is millimeters per second (mm2 S-I)
  • Dynamic viscosity (n) :
    • n=KPt,
    • Unit is millipascal seconds (mPa s)
    • where, t = time in seconds for the meniscus to fall from E to F,
    • P = mass/volume (g cm-3) obtained by multiplying the relative density of the liquid under examination by 0.998203.
    • The constant (K) of the instrument is determined on a liquid of known viscosity.
  • Density of Liquid  :
    • Find the weight of empty density bottle (P) in gram.
    • Fill the liquid up to mark.
    • Weigh the density bottle with the liquid in it (Q).
    • Find the weight of liquid by subtracting the weight of the empty density bottle (Q – P).
    • Use the weight and volume of the water to calculate density.
      • Density of  distilled water   = Weight (in gram) / Volume(in ml)
    • Unit of density is gm/ml.

5.5 Cleaning :

  • Turned the viscometer upside down and allowed to hang while the test sample drains into a trough.
  • The material remaining in the viscometer must then be removed by flushing with a suitable solvent.
  • Distilled water is an obvious choice for aqueous solutions. 
  • Then clean the viscometer with acetone because acetone is commonly used as the second solvent because of its high volatility and its ability to dissolve traces of petroleum solvents and water.
  • Dry viscometer completely before another sample is loaded.
AbbreviationExpanded form



  • Indian Pharmacopoeia