I have found this great project originally created from josepino.com. A homemade thermometer which works much like the mercury thermometer.
• A plastic film can.
• A straw.
• A wire. (Do not use iron, it rusts)
• Food colorant or beverage powder (Strawberry flavor is better).
• Glue. (Hot glue works better).
1. First, make a hole in the cap, insert the straw in the hole (be sure the straw reach the bottom of the film can) and seal it with glue or hot glue.
2. The cap should be sealed before building the thermometer.
3. Second, put 1/4 of water in the plastic film can (about half inch of water) and add some colorant.
4. Third, put the cap. If the water doesn't rise as shows the photo, you need to seal the cap perfectly.
5. Make the wire straight and put it inside of the straw.
6. The thermometer is ready to be calibrated. Calibrating this thermometer is not easy but not impossible. First, put your thermometer floating in water and measure the temperature of the water with another thermometer. Mark the level of the thermometer. The next step is to handle your thermometer in your hands and watch how the level rises. Wait for ten minutes until the water line does not rises anymore and mark it.
The top line should be 96.7F approximately, the lower line should be as marked as the calibrated thermometer indicates (usually, close to 75F)