Step 1: Understanding the Concept:
Specific gravity is the ratio of the density of a substance to the density of a reference substance (usually water). To determine the specific gravity of a solid material, especially granular or powdered ones, we need a method to accurately measure its volume, often by displacement of a liquid. The question asks for the specific instrument used for this purpose.
Step 2: Detailed Explanation:
Let's analyze the function of each piece of equipment listed:
(A) Distillation unit: This is used to separate components of a liquid mixture based on differences in boiling points. It is not used for measuring specific gravity.
(B) Platform scale: This is a type of balance used for measuring mass or weight. While mass is needed to calculate density, a scale alone cannot determine volume or specific gravity.
(C) Pycnometer: A pycnometer, also known as a specific gravity bottle, is a glass flask with a close-fitting ground glass stopper with a capillary tube through it. It is specifically designed to accurately determine the density and specific gravity of liquids and solids (especially powders and granules). The method involves weighing the pycnometer empty, then with the sample, then with the sample and filled with a liquid of known density (like water), and finally filled with the liquid alone. From these weights, the volume of the sample can be calculated by displacement, and thus its density and specific gravity can be determined.
(D) Particle analyzer: This is a broad term for instruments that measure the size distribution of particles in a sample. While related to the physical properties of granular materials, it does not directly measure specific gravity.
Step 3: Final Answer:
A pycnometer is the standard laboratory equipment used for the precise determination of the specific gravity of granular materials. Therefore, option (C) is correct.