Make a Homemade Thermometer

Making a homemade thermometer can be a little time consuming, but the process is actually quite simple to complete and easy to understand. Build your thermometer and test it to make sure that it responds to temperature changes correctly. If it seems to work, you'll also need to calibrate it before you can use the thermometer to actually measure the temperature of an unknown solution or space.

Steps

Part One: Building the Thermometer

  1. Make your measuring solution. Fill a measuring cup halfway with water and halfway with rubbing alcohol. Drop four to eight drops of liquid food coloring into the solution and mix gently to combine.[1]
    • Note that the food coloring does not alter the way that the solution reacts to temperature changes. Its only purpose is to make it easier for you to read the level of the water in the straw when you use your thermometer.
    • You could technically skip the alcohol altogether and only use water, but a thermometer containing equal parts water and rubbing alcohol will respond to temperature changes more quickly than one made with only water.
    • When determining how much solution to make, consider the volume of the bottle you will use. You will need to prepare enough solution to fill the entire bottle, plus a little extra.
  2. Pour the measuring solution into a clear bottle. Fill the bottle up to its neck by directly pouring the solution inside. Use a plastic dropper to slowly add more of the colored solution until the level of that solution reaches the very top of the bottle.
    • You can use either a glass or plastic bottle.
    • Avoid letting the solution overflow.
    • Technically, you can create a thermometer even without filling the bottle to the top. The structure of this thermometer will ensure that the solution expands into the straw instead of further into the bottle, even if the bottle is partially empty. Filling the bottle to the top, however, will cause your thermometer to respond to temperature changes faster than it might if you only filled it halfway.
  3. Insert a straw into the bottle and fix it in place. Slide the straw into the bottle, working carefully to avoid spilling any solution. Leave at least 4 inches (10 cm) of the straw sticking out from the top of the bottle and do not allow the straw to touch the bottom of the bottle. Fix it in place by molding clay around the straw and the top of the bottle.[2]
    • The clay must completely seal off the mouth of the bottle. Ideally, no air should get inside the bottle unless it comes through the straw.
    • Partially melted wax or plasticine would work if you do not have modeling clay.
    • Sealing the bottle is crucial. A tight seal prevents the liquid inside your bottle from expanding up through the mouth of the bottle, and as a result, that liquid can only expand into the straw.[3]
  4. Attach a white index card to the top of the straw. Position the card directly behind the straw and use a piece of clear tape to hold it in place.[4]
    • The index card is not strictly necessary, but using it can make it easier for you to see the level of the solution in the straw. Moreover, if you plan on calibrating your thermometer so that it can actually be used to measure temperatures, you will use this index card to mark and label the measurement values.
  5. Add measuring solution to the top of the straw. Carefully add a few drops of your colored solution into the top of the straw. When done, there should be 2 inches (5 cm) of water above the top of the bottle inside the straw.
    • By filling the straw with additional solution, you will ultimately make it easier to spot the level of the solution in the straw as it both rises and drops.
  6. Place a drop of cooking oil in the top of the straw. Use your dropper to carefully add a single drop of vegetable oil into the straw. Only use one drop.
    • Oil and water do not mix, so the oil will stay on top of the solution in the straw.
    • Adding oil to the straw prevents the solution inside from evaporating. As a result, your thermometer will remain accurate for a while after you make and calibrate it.
  7. Examine your work. The device itself is done, but before you attempt to use your thermometer, you need to double-check your work to make sure that your new measuring tool will be as accurate as possible.
    • Feel the sides of the bottle. Make sure that no moisture is leaking out from anywhere.
    • Check the clay seal at the top of your bottle to make sure that it is fairly airtight.
    • Check the straw and the index card to make sure that both are secure and will not move around during use.

Part Two: Testing the Thermometer

  1. Place your thermometer in a bowl of ice water. Fill a small bowl with cold water and a little ice. Let the water get as cold as possible, then carefully sit your thermometer inside the bowl. Make sure that you can see the liquid inside the straw very clearly.
    • When exposed to cold water, the solution in the straw should drop.
    • All matter is made of particles, and all of these particles are in constant motion. The energy involved in this motion is called kinetic energy. When the temperature of matter drops, its particles move slower and its kinetic energy decreases.
    • When you use your thermometer, you transfer the temperature and kinetic energy of the solution you test to the solution inside the thermometer. In other words, the solution in your thermometer changes to match the conditions of the solution or space being tested, and the results are visible and able to be measured.
    • Cold temperatures cause the particles in your thermometer solution to draw closer together. As a result, the liquid condenses and drops further down the straw.
  2. Place your thermometer in a bowl of hot water. Get hot tap water or heat water on the stove until it begins to steam, but not the boil. Carefully lower the thermometer into the hot water and watch the level of the liquid in the straw.
    • Note that you should give the bottle time to warm up to room temperature after you remove it from the ice bath. Do not move the bottle directly from the ice to the hot water, since the sudden change in temperature can cause your bottle to break, especially if it is made from glass.
    • When exposed to warm temperatures, the solution in the straw should rise.
    • As previously mentioned, the particles in matter speed up when heated. When the hot temperature of your tested solution gets transferred to the solution in your thermometer, the particles in your thermometer solution move faster, causing them to expand or move further apart from one another. As these particles expand, the solution rises further into the straw.
  3. Test the thermometer in other areas. Check the thermometer in various places with different temperatures. Look at how much the level rises in warm spots and how it drops in cold spots.
    • You should continue to notice that warm temperatures cause the solution to rise while cold temperatures cause it to drop.
    • Other areas worth checking out may include the refrigerator, a sunny window, an outdoor porch on a hot day or cold day, a shady spot in your yard, the inside of a car when it is not running, your basement, your garage, and your attic.

Part Three: Calibrating the Thermometer

  1. Hold a commercial thermometer next to yours. Place your thermometer in a room temperature location and allow the solution to settle to its original level in the straw. Hold a commercial alcohol thermometer next to the straw, matching the level of your thermometer solution to the level of the solution in the straw.
    • The process of calibration is essential if you want to use your homemade thermometer to actually measure temperature instead of only detecting temperature changes. If you do not calibrate and mark your thermometer, you will only be able to tell when the temperature is warmer or colder but will have no idea of what the present temperature is.
  2. Mark the temperature. With a fine point permanent marker, mark a line on your index card, directly next to the top of your solution in the straw. Label it with the current temperature, as measured by your commercial thermometer.
    • When marking the top of the solution, look closely to make sure that you are marking the top of the colored alcohol solution and not the surface of the protective layer of oil sitting on top.
  3. Repeat in areas of differing temperatures. Return the thermometer to your testing areas. Allow the solution level to rise or fall accordingly in each location, and once it does, hold the commercial thermometer next to it. Mark and label each new temperature on your homemade thermometer.
    • Measure as many different temperatures as possible. The more temperatures you can include on your thermometer gauge, the easier it will be to identify the temperature of an unknown solution or atmosphere.
  4. Use your calibrated thermometer to find an unknown temperature. Once you have a decent range of temperatures marked on your thermometer, take your instrument to a warm or cold location and set it down. Wait for the solution level to rise or fall, and when it stops, look at the calibration marks on your straw. Use these previous measurements to determine the temperature of the area in which your thermometer presently sits.
    • To double-check the accuracy of your thermometer, check the temperature of the location using your commercial thermometer after recording the measurement you got with your homemade thermometer.
    • At the completion of this step, your homemade thermometer is done and officially ready for use.

Warnings

  • Be careful when working with rubbing alcohol. Do not allow the alcohol to come in contact with your eyes and do not ingest it.

Things You'll Need

  • Tap water
  • Rubbing alcohol
  • Food coloring (any color)
  • 4 cup (1 L) measuring cup OR 600 ml beaker
  • Clear glass or plastic bottle, 8 to 10 inches (20 to 25 cm) tall
  • Clear plastic straw, at least 8 inches (20 cm) tall
  • Plastic dropper
  • Vegetable cooking oil
  • Modeling clay, wax, or plasticine
  • Ruler
  • Fine-point marker
  • White index card
  • Clear tape
  • Bowl of cold water
  • Bowl of hot water
  • Commercial thermometer (for calibration)

Sources and Citations

  1. ↑ http://www.energyquest.ca.gov/projects/thermometer.html
  2. ↑ http://assets.pearsonschool.com/asset_mgr/current/201237/tx_sci_G6_lab.pdf
  3. ↑ http://www.hometrainingtools.com/make-thermometer-science-project/a/1533/
  4. ↑ http://publish.uwo.ca/~cagis/experiments/thermo.htm
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