How to Build an Outdoor Thermometer

A thermometer is any device that measures temperature. A fluid thermometer is one the oldest types of thermometer and still one of the most common for general outdoor use. This type of thermometer relies on the general rule that liquids expand as their temperature increases. The fluid in a thermometer must remain a liquid throughout the temperature range that the outdoor thermometer will encounter. The most common types of liquid for this purpose are mercury or a mixture that contains alcohol.

Things You'll Need

• Clear drinking straw
• Colored tape
• Commercial thermometer
• Food coloring
• Hammer
• Jar (thin and narrow)
• Plumber's putty
• Nail
• Rubbing alcohol
• Ruler
• Thin waterproof marker
• Water

Instructions

1. Mix a solution of half water and half rubbing alcohol to provide an effective thermometer fluid. Plain water does not expand enough to register small temperature changes well, while pure alcohol expands too much over a modest temperature change.

2. Add a few drops of food coloring to the solution you mixed in Step 1. This will make the level of the thermometer fluid easily visible when it moves up and down through the straw. Fill the jar 1/8 to 1/4 full with the thermometer fluid. This level should provide enough fluid to move up the straw in response to a temperature increase, but not so much that it overflows the straw when it gets hot.

3. Hammer a nail through the center of the lid. The nail should create a hole just large enough for the straw to pass through. Place the straw in the jar so the bottom end is below the surface of the fluid but doesn't touch the bottom of the bottle. This will allow the fluid to move in and out of the straw as the temperature changes.

4. Form a watertight seal around the straw with plumber's putty. Plumber's putty is waterproof and remains flexible over a wide range of temperatures. You should now be able to observe the fluid move up the straw when it gets hot and down when it gets cold.

5. Calibrate the thermometer you just made against the commercial thermometer. Mark at least two different temperatures to obtain a scale for the thermometer you just made. Measure the distance between these marks and label a long piece of tape with a temperature scale based on this distance. Peel off the back of the tape and carefully fix it to the straw so that the temperatures on the label match those of the commercial thermometer. Place the thermometer outside under a porch roof so that it doesn't rain on your thermometer.

References

• California Energy Commission