How to Measure Specific Gravity Using a Specific Gravity Bottle?

A specific gravity bottle (also known as a density bottle or relative density bottle) allows you to accurately determine the specific gravity of a liquid by carefully measuring the masses of the empty bottle, the bottle filled with the liquid in question, and the bottle filled with water, and then applying a simple formula. Here's a step-by-step guide:

Steps to Measure Specific Gravity

1. Clean and Dry the Specific Gravity Bottle:

   • Thoroughly clean the specific gravity bottle and its stopper. Ensure it is completely dry. Any residue or moisture will affect the accuracy of your measurement.

2. Weigh the Empty Bottle:

   • Weigh the clean, dry, and empty specific gravity bottle using an accurate balance. Record this weight as m₁ (mass of empty bottle).

3. Fill with the Reference Liquid (Water):

   • Fill the specific gravity bottle completely with distilled water at a known temperature (e.g., 20°C). Ensure there are no air bubbles trapped inside. Insert the stopper carefully, allowing excess water to overflow through the capillary tube.

4. Dry the Exterior and Weigh:

   • Thoroughly dry the outside of the bottle to remove any adhering water. Weigh the bottle filled with water and record this weight as m₂ (mass of bottle + water).

5. Empty and Dry the Bottle Again:

   • Empty the bottle completely and ensure it is thoroughly dried before proceeding. This is crucial to avoid contamination.

6. Fill with the Test Liquid:

   • Fill the bottle completely with the liquid whose specific gravity you want to determine, ensuring no air bubbles are present. Insert the stopper, allowing excess liquid to overflow.

7. Dry the Exterior and Weigh:

   • Dry the outside of the bottle completely. Weigh the bottle filled with the test liquid and record this weight as m₃ (mass of bottle + test liquid).

8. Calculate the Specific Gravity:

   • Use the following formula to calculate the specific gravity of the liquid:

   Specific Gravity = (Mass of Test Liquid / Volume) / (Mass of Water / Volume)

   Since the volume is the same for both water and the test liquid (the volume of the specific gravity bottle), the formula simplifies to:

   Specific Gravity = (m₃ - m₁) / (m₂ - m₁)

   Where:

   • m₁ is the mass of the empty bottle.
   • m₂ is the mass of the bottle filled with water.
   • m₃ is the mass of the bottle filled with the test liquid.

Example Calculation

Let's say:

• m₁ (mass of empty bottle) = 20 g
• m₂ (mass of bottle + water) = 70 g
• m₃ (mass of bottle + test liquid) = 65 g

Specific Gravity = (65 g - 20 g) / (70 g - 20 g) = 45 g / 50 g = 0.9

Therefore, the specific gravity of the test liquid is 0.9.

Important Considerations

• Temperature Control: Maintain a constant temperature throughout the experiment. Specific gravity is temperature-dependent, so variations will affect your results. Record the temperature at which measurements are taken.
• Accuracy of Balance: Use a balance with sufficient accuracy to ensure reliable results. A higher precision balance will give more accurate results.
• Air Bubbles: Ensure there are no air bubbles trapped in the bottle when filled with either water or the test liquid, as these will affect the volume and hence the density measurement.
• Cleanliness: Keep the bottle meticulously clean to avoid contamination.
• Calibration: Regularly check the calibration of your specific gravity bottle.

By following these steps carefully, you can accurately determine the specific gravity of a liquid using a specific gravity bottle.