Soil – Part 6

An Experiment to investigate components of a Soil Sample (Sedimentation experiment)

Requirements (apparatus and materials):

• Garden soil, measuring cylinder, stirring rod and water

Procedure

• Add a known volume of water to the soil in a measuring cylinder.
• Put some soil in the cylinder
• Mix the soil thoroughly with a stirring rod.
• Leave the experiment to settle for some time, about 15 minutes.
• Record your observation

Note: step one and two are interchangeable.

Setup of the Apparatus and observation

Observation

When the mixture settles, the soil particles arrange themselves according to particles size, with the heaviest particles on at the bottom and the lightest on top. So the oder from bottom is; coarse gravel and sand settle first then silt and finally clay particles. Humus settles on top of all the other particles.

The proportions of mineral constituents in the soil sample can be estimated by measuring the depth of each layer, relating it to the total depth of the layers as shown in the diagram.

Experiment to determine the presence of air in soil (and percentage of air in soil)

Materials

Water, stirring rod, soil measuring cylinder

 Procedure

Pour water (50cm3) in a measuring cylinder and note the level. Add 50cm3 of soil to it to make the level of water rise up to the 100cm3 mark. Note this level, stir the soil in water until all the soil mixes with water and no more bubbles are evolved. Leave it to settle and note the final level of water and soil.

Note; water could be added to soil instead of adding soil to water

Observation

The water level rises to a high level called initial level and after stirring the level falls progressively until no further fall. This level is called the final level. Bubbles are given off.

Conclusion

Soil contains air, which is equal to the difference between the initial and final levels.

Determining percentage of air in a soil sample

Results

Volume of soil = 50cm³

Volume of water = 50cm³

Initial volume of water +soil = 100cm³

Final volume of soil +water=85cm³

Volume of air in soil = (100-85) cm³

Percentage of air in soil = volume of air/ volume of soil

                                      = 15/50 x100

                                      =   30%

Questions

1. A sample of soil was poured into a measuring cylinder containing water and the mixture stirred. The readings taken were as follows:

Volume of water in the measuring cylinder      = 215 cm³

Volume of water + soil                                        = 260 cm³

Volume of water + soil after stirring                 = 250 cm³

(a) Calculate the volume of soil. (03 marks)
(b) Calculate the volume of air. (03 marks)
(c) What was the percentage of air in the soil? (04 marks)

2. In an experiment to determine the percentage of air in a soil sample, the following results were obtained.

Volume of soil added to measuring cylinder       = 40 cm³

Volume of water added to measuring cylinder   = 40 cm³

Volume of soil and water after stirring                = 75 cm³

(a) Calculate the volume of air. (03 marks)
(b) What is the percentage of air in the soil sample? (03 marks)
(c) What is the importance of soil air? (04 marks)