Study carefully the experimental set-up labelled A and use it to answer questions (a) - (d) (a) State the aim of the experimental set-up. (b) Describe brief...

Answer Details

(a) Aim of the experiment

To determine the different soil particles (fractions) present in a soil sample, and hence its soil texture.

(b) Procedure

• A measured quantity of the soil is put into a measuring cylinder and sufficient water is added.
• A small quantity of hydrogen peroxide (or sodium bicarbonate) is added to disperse the particles and remove organic matter.
• The cylinder is stirred and shaken vigorously so that the soil is thoroughly mixed with the water.
• The mixture is then allowed to stand undisturbed for at least five hours to settle.

(c) Observation

• The soil particles settle in layers according to their weights and sizes.
• Gravel settles first at the bottom, followed by coarse sand, then fine sand, then silt, with the fine clay settling last on top.
• The organic matter (humus) floats on the surface of the water.

(d) How the different soil particle sizes can be estimated

• Read the total height of the sediments directly from the measuring cylinder, \(T\).
• Read the height of the sand layer, \(H_{SA}\), the silt layer, \(H_{SI}\), and the clay layer, \(H_{CL}\).
• Calculate the proportion of each fraction as a percentage of the total: \[ \%\,\text{sand} = \frac{H_{SA}}{T}\times 100, \quad \%\,\text{silt} = \frac{H_{SI}}{T}\times 100, \quad \%\,\text{clay} = \frac{H_{CL}}{T}\times 100. \]