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