RPSC Agriculture Research Officer (Agriculture Chemistry) - 2024

The scattering of light by colloidal particles that makes their illuminated path visible is known as the Tyndall effect.

• Brownian movement: The continuous random zigzag kinetic motion of colloidal particles caused by unequal collisions with dispersing solvent molecules.
• Tyndall effect: The optical phenomenon where colloidal particles scatter a focused beam of light, causing the path of the beam to become luminous and distinct.
• Flocculation: The coagulation or clumping together of dispersed colloidal particles into larger aggregates.
• Cataphoresis: The electrophoretic movement of positively charged colloidal particles toward the cathode under an applied electric gradient.

The Cunninghamella plaque method developed by Adolf Mehlich is a microbiological bioassay used to evaluate available soil phosphorus.

• Boron: Evaluated biologically via the sunflower pot culture technique (Colwell method).
• Phosphorus: Adolf Mehlich (1934) used the fungus Cunninghamella blakesleeana grown directly on soil plaques; the colony diameter directly reflects available phosphorus levels.
• Potassium: Commonly estimated using Aspergillus niger bioassay.
• Copper and magnesium: Microbiologically assayed using Aspergillus niger (Mulder method).

The aqueous solubility of gypsum (CaSO4·2H2O) at 0 °C is 0.241 g per 100 mL of water.

• 41 g: Solubility of gypsum per 1000 mL (1 litre) of water.
• 24.1 g: Highly exaggerated value; gypsum is only sparingly soluble.
• 0.241 kg: Exceeds true gypsum solubility by a factor of one thousand.
• 0.241 g: At 0 °C, exactly 0.241 g of calcium sulfate dihydrate dissolves in 100 mL of pure water (~2.41 g/L).