Experiment No.4: Grain size
analysis
Part II: Hydrometer analysis.
-Hydrometer analysis is the procedure generally
adopted for determination of the particle-size
distribution in a soil for the fraction that is finer
than No. 200 sieve size (0.075 mm).
The lower limit of the particle-size determined
by this procedure is about 0.001 mm.
tools
1- Sensitive balance.
2- Hydrometer.
3- Control cylinder.
4- Sedimentation cylinder.
5- Thermometer.
6- Mixer.
7- Stop watch.
Procedure
• Dry the sample ( which passed sieve # 200 ) in an oven,
then take ( 50 gram ) of it to do the hydrometer test
on it .
• Prepare two cups filled with 125 mL water , then add
to one of them Sodium Hexametaphosphate
substance ( so that the concentration become 4 % , so
for this cup we need 5 gram of the substance ) .
• Put one of the two cups in the control cylinder and add
water to 1000ml.
• Put the Hydrometer in the control cylinder and wait
until it is rest at the water then tack its reading – this
reading called Zero Condition - .
• Put the soil in the other cup , then we have to mix it slurry – in a mixer for 5 minutes with adding water to
the mixer till we fill half of the mixer .
• Move the soil to the sedimentation cylinder and add
water to 1000 ml.
• Close the cylinder then we have to rotate it 30 times in
a minute and wait a bit, then put the Thermometer
and the Hydrometer in the sedimentation cylinder .
• Record the value of the Temperature and take the
reading of the Hydrometer after specific periods of
time – these time periods depend on the specifications
of the experiment (1,2,4 ,....) minutes – then keep
recording the Hydrometer readings at the specific
times till the Hydrometer reading reach the Zero
Condition reading .
•
•
•
•
•
1 min T=20 C Ra= 47mm
2 min T=20 C Ra= 42mm
4 min T=20 C Ra= 37mm
8 min T=20 C Ra= 32mm
16 min T=20 C Ra= 29mm
45
40
35
% passing
30
25
20
15
10
5
0
1
0.1
0.01
Grain Size ( mm )
0.001