Measurement of viscosity:

General principle:

     The measurement of viscosity of liquid is based on pioseulle's equation.

               n=πPtr^4/8VI

Where:

   V= volume of liquid

    r= radius of capillary tube

    l= length of tube

   P= pressure applied

Measurement of absolute viscosity:

 It is difficult to measure  directly the exact value of absolute viscosity because measurement of p,r and v is difficult.

So the viscosities of liquids are expressed in relative term

relative viscosity:

          "This is the ratio of viscosity of liquid to the viscosity of water taken as reference standard and this is called relative viscosity.

OSTWALD's VISCOMETER (measurment of relative viscosity):

It is used to measure the relative viscosity.

• It is a U- shaped glass tube with two marks 'x'&'y'.

•It has two bulbs 'A' and 'B'.

•The bulb A is at higher level than B.

•A definite volume of liquid is put in bulb B and then sucked in bulb A.

•The time of flow of liquid is noted .Similarly the time of flow of reference liquid water is also noted.

•Density of liquid is determined by "Specific gravity bottle".

•Follow8ng equation is applied to calculate Viscosity.

       n°/n= d°/d × t°/t

Where:

n°= viscosity of liquid

 n= viscosity of relative liquid

d°= density of liquid determined by Specific gravity bottle

d=density of reference liquid

t°=time of flow of liquid

t= time of flow of reference liquid