Pycnometer method,water content by Pycnometer Detailed study of Pycnometer meter method for determining water content

 Detailed study of Pycnometer method for determining water content ..

Pycnometer 

Volume of Pycnometer = 900 ml 

Top conical cap = made by brass metal 

Central hole of the top = 6 mm.

Limitations of Pycnometer method for water content 

(1)-one  must have to know about specific gravity for using this method .

(2)-It is defined only cohesionless soil.

(3)-This method does not use in cohessive soil 

***because when we stirring the soil then air does not remove due to interlocking if soil particles in cohessive soil. 

Apparatus required

Pycnometer

Weighing balance with an accuracy of 1.0g

Glass rod

Vacuum pump

Method .

1- Take empty Pycnometer and Weight it.(M1)

2-Put a moist soil in an empty Pycnometer and Weight.(M2).

Note .

Moist soil means combination of solid particles,Water and air .

3- stirring the soil and continue filling water into Pycnometer so that air completely remove from voids and weight it .it is M3.

4- Now fill the empty Pycnometer with water and weight.(M4).

Now mass if water Mw= (M2-Md)-M1 

 w%= (mass of water/mass of solid) 

       = (M2-Md)-M1/Md .

But here we don't know Md..

For Md 

We know that volume of solid= Md/ρs

                                             =Md/Gρw 

 Note ρs=Gρw

Volume of water equivalent to solid=Md/Gρw 

Now mass of water =(Md/ Gρw)ρw 

                     = Md/G.

Now M4=M3-Md+Md/G

M3-M4=Md-Md/G.

M3-M4=Md(G-1)/G 

Md=(G/G-1)xM3-M4 

Now water content w% =(M2-Md)/Md-M1 

= (M2-M1)/Md-1 

w%= (M2-M1)/(M3-M4){G-1}/G-1 

This shows that without specific gravity G we can't determine the water content by Pycnometer.

Also see...

Soil formation ......

Specific gravity of soil ....