Which of the following is determined with the help of pycnometer?

Detailed Explanation

A pycnometer is a specially shaped, wide-mouthed bottle (typically of about 900 ml capacity) fitted with a conical, perforated cap that allows air bubbles to escape while excess water/soil slurry is expelled through the small hole in the cap, ensuring a precisely repeatable fill volume. It is used in the laboratory to determine two related quantities for a soil sample: the water content and the specific gravity of solids.

The method involves weighing the pycnometer empty, with soil alone, with soil and water (topped up to the mark), and with water alone (topped up to the mark) — from these four weighings, both the water content and specific gravity can be calculated using standard formulas.

Key Concepts for Students

• Pycnometer method determines both water content and specific gravity from the same set of weighings, making it an efficient combined test.
• The device is more commonly used for coarser (sandy) soils; fine-grained soils typically use the smaller 50 ml density bottle instead (see Q23).
• The perforated conical cap ensures a precise, repeatable fill volume each time, which is essential since the calculation relies on comparing weights at a fixed total volume.
• Removing entrapped air (by shaking, stirring, or applying gentle heat/vacuum) before the final weighing is critical for accurate results.