Making of lactometer in Floating bodies – Class 9 Science Experiment

Chapter Name: Floating bodies

Activity Name: Making of lactometer in Floating bodies

Activity Description:

Making of lactometer in Floating bodies - Class 9 Science Experiment

This experiment aims to create a simple device called a lactometer, which can be used to test whether water is added to milk or not.

The lactometer is essentially a makeshift hydrometer/densitometer. The experiment involves observing the behavior of a ball pen refill when submerged in water, milk, and a mixture of milk and water.

Required Items:

  • Ball pen refill with a metal point
  • Boiling tube
  • Water
  • Milk
  • Pen for marking

Step by Step Procedure:

  1. Take an empty ball pen refill with a metal point.
  2. Fill a boiling tube with water.
  3. Gently place the refill in the boiling tube with the metallic point inside the water. If the refill does not stand vertically, find a way to make it stand upright (not touching the tube’s wall) and note down how you achieve this.
  4. Observe whether the refill sinks completely or if some part remains above the water surface. Use a pen to mark the point on the refill indicating the part above the water surface.
  5. Empty the boiling tube and fill it with milk.
  6. Float the refill in the milk and observe whether it sinks to the same mark as it did in water. If not, note whether it sinks more or less and explain why you think this happened.
  7. Put a second mark on the refill, indicating the part above the surface of the milk.
  8. Create a mixture of milk and water and pour it into the boiling tube.
  9. Guess to which point the refill will sink when placed in this mixture.
  10. Test your guess by actually submerging the refill in the milk-water mixture.
  11. Consider whether this lactometer can be used to determine if water is added to milk.

Experiment Observations:

  1. The refill sinks in water and some part remains above the water surface.
  2. When floated in milk, the refill may sink more or less than it did in water, and the reasons for the difference are to be noted.
  3. The refill is then tested in a milk-water mixture to observe its sinking behavior.


  1. Handle the boiling tube and the refill carefully to avoid any breakage.
  2. Ensure the boiling tube is clean and free from any contaminants before filling it with liquids.
  3. Make sure the marks on the refill are clear and accurate for proper observations.

Lesson Learnt from Experiment:

This experiment demonstrates how a simple lactometer can be created using a ball pen refill to determine whether water is added to milk. It also introduces the concept of density and how objects float or sink based on their density compared to the liquid they are placed in.

Additionally, the experiment hints at the use of professional instruments like hydrometers/densitometers to measure the density of various liquids.

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