How to make a Thermometer
Here is an easy-to-build homemade thermometer using materials available at home. (3/12/2006)
I built this thermometer in about one hour, just for fun. This one is not intended to be exact, but works fine. I made this one based in my experience from school.
Before we start, let's review a little about the history of the thermometer:
"The thermometer is a device that measures temperature or temperature gradient using a variety of different principles; it comes from the Greek roots thermo, heat, and meter, to measure. A thermometer has two important elements: the temperature sensor (e.g. the bulb on a mercury thermometer) in which some physical change occurs with temperature, plus some means of converting this physical change into a value (e.g. the scale on a mercury thermometer).
Various authors have credited the invention of the thermometer to Avicenna, Cornelius Drebbel, Robert Fludd, Galileo Galilei or Santorio Santorio. The thermometer was not a single invention, however, but a development.
Philo and Hero of Alexandria knew of the principle that certain substances, notably air, expand and contract and described a demonstration in which a closed tube partially filled with air had its end in a container of water.
Such a mechanism was later used to show the hotness and coldness of the air with a tube in which the water level is controlled by the expansion and contraction of the air. These devices were developed by Avicenna in the early 11th century, and by several European scientists in the 16th and 17th centuries, notably Galileo Galilei. As a result, devices were shown to produce this effect reliably, and the term thermoscope (Galileo thermometer) was adopted because it reflected the changes in sensible heat (the concept of temperature was yet to arise). The difference between a thermoscope and a thermometer is that the latter has a scale. Though Avicenna or Galileo are often said to be the inventor of the thermometer, what they produced were thermoscopes.
The first clear diagram of a thermoscope was published in 1617 by Giuseppe Biancani: the first showing a scale and thus constituting a thermometer was by Robert Fludd in 1638. This was a vertical tube, with a bulb at the top and the end immersed in water. The water level in the tube is controlled by the expansion and contraction of the air, so it is what we would now call an air thermometer." Ok.. Ok... too much blah blah blah. Let's start.
Materials Needed:* A plastic film can.
* A straw.
* A wire. (Do no use iron, it rusts)
* Food colorant or beverage powder (Strawberry flavor is better, I like 'dulce de fresa' flavor).
* Glue. (Hot glue works better).
First, Make a hole in the cap, insert the straw in the hole (be sure the straw reach the botton of the film can) and seal it with glue or hot glue.
The cap should be sealed before building the thermometer.
Second, put 1/4 of water in the plastic film can (about half inch of water) and add some colorant.
Third, put the cap. If the water doesn't rise as shows the photo, you need to seal the cap perfectly.
Make the wire straight and put it inside of the straw.
The thermometer is ready to be calibrated. Calibrating this thermometer is not easy but not impossible. First, put your thermomether 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)
I used a computer to get the scale for my homemade thermometer, but it can be done easily using a ruler.
How this home-made thermometer works:
A non-electronic thermometer have mercury (liquid metal) inside. As the temperature rises, the metal expands. My thermometer is simple, it uses air.
Don't be fooled with the liquid in my thermometer. The water with colorant is only a seal. When the air inside of the film can gets warm, it expands and pushes the liquid. That is the reason why the cap should be sealed.
The wire in the straw helps to break the surfase tension of the water and makes the water to rise easily.
There is other ways to make a thermometer, the most fascinating one for me is the galileo thermometer. I hope someday I will be able to build one.
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