Pycnometer method for Specific Gravity IS‑code (IS 2720: Part 3/Section 2, 1980)

 IS‑code (IS 2720: Part 3/Section 2, 1980) pycnometer method  

Objective 

To determine the specific gravity (Gs) of soil solids using a pycnometer (1 L gas jar).  

Reference 

IS 2720 (Part 3/Sec 2): 1980 — Determination of Specific Gravity: Fine, Medium & Coarse‑Grained Soils.  

 

Apparatus 

• Gas jar (pycnometer), ~1 L, with rubber bung/stopper and ground‑glass plate or plastic slip cover 

• End‑over‑end mechanical shaker (~50 rev/min) (or a suitable vibrating shaker) 

• Balance readable/accurate to 0.2 g 

• Thermometer 0–50 °C, readable/accurate to 1 °C 

(A gas jar is an effective pycnometer provided the mouth can be sealed so the volume is constant.)  

 

Sample 

• 200 g for fine‑grained soils; 400 g for medium/coarse‑grained soils. 

• Use a disturbed sample that has been oven‑dried and cooled (if loss of water of hydration is a concern, dry at ≤ 80 °C and report). 

• Not suitable if the soil has > 10 % stones retained on 40‑mm IS sieve (break such stones to < 40 mm).  

 

Symbols (masses) 

• m₁ = mass of dry gas jar + plate 

• m₂ = mass of gas jar + plate + dry soil 

• m₃ = mass of gas jar + plate + soil + water (filled and sealed, no air) 

• m₄ = mass of gas jar + plate + water only (filled and sealed, no air)  

 

Procedure (Step‑by‑step) 

1. Dry & weigh the container 

Dry the gas jar and plate. Weigh to the nearest 0.2 g → m₁.  

2. Add dry soil & weigh 

Quickly add ~200 g (fine) or 400 g (medium/coarse) of the oven‑dried soil to the jar. Put the plate on and weigh → m₂.  

3. Add water 

Add about 500 mL water at a temperature within ±2 °C of the average room temperature during the test. Insert the rubber stopper. 

1. For medium/coarse soils: stand ≥ 4 h after adding water. 

2. For fine soils: proceed directly.  

4. Disperse & shake 

First hand‑shake to suspend particles, then place on the mechanical shaker for 20–30 min.  

5. Top up, seal without air & weigh 

6.  Remove the stopper. Rinse any adhering soil from stopper and rim back into the jar; disperse froth with a fine water spray. 

7.  Fill to brim, allow soil to settle a few minutes, then top up to a convex meniscus and place the plate carefully so no air is trapped. Dry outside and weigh → m₃.  

8. Jar full of water only & weigh 

Empty and wash the jar. Fill completely with water only, place plate with no air, dry outside and weigh → m₄.  

9. Replicates 

Perform three determinations on the same soil (independent runs). Use the average as the reported value; if any result differs by > 0.03 from the average, repeat the test(s).  

 

Calculation 

G=(m1-m2)/((m1-m2)-(m3-m4))

Apply temperature correction to 27 °C if needed: 

Report G′ at 27 °C to the nearest 0.01.  

 

Reporting (as per IS) 

• Specific gravity at 27 °C (G′), to 0.01. 

• Number of determinations (≥ 3) and average value. 

• Any deviations (e.g., drying at ≤ 80 °C) and the test temperature used for correction.  

 

Practical notes (from IS) 

• Ensure the seal traps no air under the plate. 

• Keep water temperature within the stated range; if room and water temperatures differ greatly, draw enough water and let it stand in the lab to stabilize before testing. 

• An end‑over‑end shaker is specified, but a suitable vibratory shaker may be used depending on the pycnometer type.  

 

Quick calculation template (fill your masses in grams) 

• m₁ = ___ 

• m₂ = ___ 

• m₃ = ___ 

• m₄ = ___ 

• G=(m1-m2)/((m1-m2)-(m3-m4))

• Water temp = ___ °C → K = ___ → G′ = K·G