How to Make a Homemade Thermometer?

Take a clear plastic bottle and add tap water and rubbing alcohol in a one to one ratio til you have filled a quarter of the bottle. Add a some food coloring and stir to distribute the dye. Place a clear drinking straw into the bottle but don’t let it touch the bottom. Then use modeling clay to seal the bottle and also it will keep the straw in place. Now watch what happens if you heat the bottle.