Here are your supplies. Go to the counter and get one vial, one plastic cup, one small plastic zip bag, one 50 mL syringe, and one bulb pipette.
Fill the vial with 25 mL of room-temperature water. Let the vial stand for 1 minute undisturbed, so that the water stops moving.
Carefully place the vial with room temperature water on the bottom of the plastic cup.
Use a bulb pipette to take up a bulbful of cold water (blue).
Gently squeeze the bulb to release the cold blue water on the bottom of the vial. This must be done very carefully. Do not jiggle the vial. Observe the vial to see if the blue water floats or sinks.
Take the 50 mL syringe and draw up 25 mL of hot water from the tea kettle. Be careful not to burn yourself.
Fill the zip bag with the 25 mL of hot water. Seal the top of the bag tightly.
Slowly lower the bag of hot water into the cup with the vial and observe what happens to the blue water.