TO make a lactometer with ball point refill, follow the given steps : 1. Take an empty ball pen refill with a metal point at the bottom. 2. Take a boiling tube and fill it with water. 3. Put the refill in the water with metallic point. 4. To make the refill stand in water, insert a small eraser piece in the refill at the centre. 5. Mark the point with marker up to which the refill is above the water. 6. Now, empty the boiling tube with water and fill it with milk. 7. Again put the refill in milk and mark the point which shows the part which is above the surface of milk. 8. Further we can add , milk water mixture in the boiling tube and repeat the same step 8. 9. we can now compare and test whether water is added to milk or not.