Study carefully the experimental set-ups labelled A, B and C. (a) What is the aim of the experiment for which the apparatus has been set up? (b) List the ex...

(a) Aim of the experiment: The apparatus is set up to compare the capillary attraction (capillarity) of different soil types, that is, to determine and compare the rate and height to which water rises through samples of clay, loam and sandy soil.

(b) Order in which water has risen, starting with the highest:

• Set-up C (sandy soil) - highest
• Set-up A (loamy soil) - middle
• Set-up B (clayey soil) - lowest

Within the time allowed for the experiment, water rises fastest and highest through the coarse sand; over a much longer period the order would change as the clay absorbs and holds more water.

(c) Six items of apparatus used:

• A large beaker, basin, dish or trough
• Three capillary (glass) tubes
• Soil samples A, B and C (clay, loam and sand)
• Water
• Cotton wool
• Clamps and retort stands

(d) Procedure:

1. Take three glass tubes and plug each at the lower end with cotton wool.
2. Dry the soil samples and break up the lumps into fine particles.
3. Fill each tube with an equal quantity of the dry clayey, loamy and sandy soil respectively.
4. Fix the three tubes upright with the clamps and retort stands.
5. Dip the lower ends of the three tubes to the same depth into the trough of water.
6. Allow the set-up to stand for the required time.
7. Watch the upward movement of water into each soil sample and record the height of rise in each tube.

(e) Reason for the difference in water levels between B and C: In set-up C (sand), the larger particles and wider pore spaces allow water to rise quickly by capillarity, but the rise soon stops because the large pores give only weak capillary attraction. In set-up B (clay), the very fine particles and tiny pore spaces let water rise only slowly at first; but as the clay particles absorb water and swell, the capillary attraction becomes stronger, so given more time the water eventually rises higher in the clay than in the sand. The difference in water level is therefore due to the difference in particle size and pore space of the two soils.