Explore our General Test Procedure (GTP) for viscosity testing. Follow our step-by-step instructions to achieve precise and reliable viscosity measurements.

Viscosity Test Procedure

1.0     Objective

• • The objective of this General Test Procedure (GTP) is to describe the procedure to be used for performing Viscosity test.

2.0     Principle

• • Viscosity is a property of a liquid, which is closely related to resistance to flow.

• • It is defined in terms of the force required to move one plane surface continuously past another under specified steady state conditions when the space between is filled by the liquid in question.

• • It is defined as the shear stress divided by the rate of shear strain.

3.0     Requirements for Viscosity Test

• • Apparatus: Suitable Viscometer

• • Clean and fry beaker (capacity 600ml)

• • Clean and dry glassware for dilution (capacity: mention in standard test procedure)

• • Purified water or specified in individual monograph.

4.0     Procedure for Viscosity Test:

• • Select the spindle of angular velocity or speed mentioned in the individual specification.

• • Condition the syrup / suspension or solution of the substance under test suitability taken in 600 ml beaker to the required temperature & immerse the spindle not touching form the walls of the beaker.

• • Start the viscometer & note the reading form the dial after stabilization.

• • For Finished Product:

• • Measure the viscosity for syrup or suspension, taken the under test sample in 600 ml beaker, fill the fluid up to the mark.

• • Measure the viscosity at 25ºC ± 0.5º, using spindle no. 3 on 50 RPM, and note down the reading form the dial after stabilization.

Viscosity (in cPs) = Dial reading

• • Viscosity measurement may be carried out by the following methods. For method selection, refer the standard test procedure.

• Method A (Using Rotating Viscometer) (Brookfield Viscometer)

  • The rotating viscometer measures the sharing force in a liquid medium placed between two coaxial cylinders one of which is driven by a motor & the other is caused to revolve by the rotation of the first.

• • Under the conditions, the viscosity becomes a measurement of the angle of deflection of the cylinder to revolve, expressed in newton meters.

• Method B {(Capillary Type Viscometers) (Ostwald Type Viscometer)}

  • Viscometer:

• • The apparatus consists of a glass U-tube viscometer made of clear borosilicate glass and constructed in accordance with the dimensions shown in the figure and in table.

• • The monograph states the size of viscometer to be used.

• • Method I:

• • Fill the viscometer with the liquid being examined through tube L to slightly above the Mark G, using a long pipette to minimize wetting the tube above the mark.

• • Place the tube vertically in a water bath and when it has attained the specified temperature.

• • Adjust the volume of the liquid so that the bottom of the meniscus settles at the mark G.

• • Adjust 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 form the top edge of mark E to the top edge of mark F.

• Calculate, as required either the kinematic viscosity (n) in square millimeters per second (mm² s^-1) from the expression:

N= kt,

• Or the dynamic viscosity (h) in milipascal seconds (mPas) from the expression:

h = Krt,

Where,

t = time in seconds for the meniscus to fall form E to F,

r = mass/volume (g cm^-3) obtained by multiplying the relative density, of the fluid being examined by 0.9982.

The constant (K) of the instrument is determined using the appropriate reference liquid for viscometers.

• • Method II (Capillary Viscometer Method)

  • The determination of viscosity using a suitable capillary viscometer is carried out at a temperature of 20 ± 0.1 ºC, unless otherwise prescribed.

• • The time required for the level of the liquid to drop from one mark to the other is measured with a stop watch to the nearest one-fifth of a second.

• • The result is valid only if two consecutive readings do not differ by more than 1 per cent.

• • The average of not fewer than three readings gives the flow time of the liquid to be examined.

• Calculate the dynamic viscosity h in milipascal seconds using the formula:

n = kpt

k = constant of the viscometer, expressed in square millimeters per second square.

r = density of the liquid to be examined expressed in milligrams per cubic millimeter, obtained by multiplying its relative density (d²⁰20) by 0.9982,

t = flow time, in seconds of the liquid to be examined.

The constant K is determined using a suitable viscometer calibration liquid.

To calculate the kinematic viscosity (mm² s^-1), use the following:

v = kt.

The determination may be carried out with an apparatus having the specifications.

The minimum flow time should be 350s for size no. 1 and 200s for all other sizes.

• Method:

  • Fill the viscometer through tube (L) with a sufficient quantity of the liquid to be examined, previously brought to 20ºC unless otherwise prescribed, to fill bulb (A) but ensuring that the level of liquid in bulb (B) is below the exit to ventilation tube (M).

• • Immerse the viscometer in the bath of water at 20 ± 0.1ºC, unless otherwise prescribed.

• • Maintain it in the upright position and allow to stand for not less than 30 min to allow the temperature to reach equilibrium.

• • Close tube (M) and raise the level by closing tube (N) up to a level about 8 mm above mark (E).

• • Keep the liquid at this level by closing tube (N) and opening tube (M). Open tube (N) and measure, with a stop watch to the nearest one-fifth of a second, the time required for the level of the liquid to drop from mark (E) to (F).

• Precautions during Viscosity Measurement:

  • Measurement of viscosity of solutions of the high viscosity types of Methylcellulose is a special case, since they are too viscous for the commonly available viscometers.

• • The viscometer may be adapted to the measurement of the ranges of viscosity encountered in Methylcellulose solutions.

• • Viscometer should be clamped to the stand in order to avoid any external disturbance.

• • Viscosity changes significantly with temperature, hence temperature should be constant throughout the operation, as far as practically possible. In general viscosity decreases as temperature is raised.

• • Calibrate the instrument with a liquid of known viscosity and determine the viscosity of the unknown liquid by comparison with that of known.