Experiment No.4: Grain size analysis

Part II: Hydrometer analysis.

-Hydrometer analysis is the procedure generally adopted for determination of the particle-sizedistribution 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

0.0010.010.10

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Grain Size ( mm )

% p

assin

g