Be a Scientist: Make Your Own Thermometer




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About 300 years ago, Daniel Fahrenheit made and calibrated the first reliable thermometers. Some people* still use the scale he developed; the Fahrenheit Scale.

*like Americans ;-)

Step 1: Materials and Tools.

You need a small air-tight container (a 35mm film cannister is perfect), a thin translucent or transparent tube (such as an empty biro ink-tube), food colouring and something to make and seal a hole.

If you are going to add a scale, you will also need a piece of white card, clear sticky-tape and a narrow marker (an OHP pen is good).

Step 2: Make It.

Make a small hole in the middle of the cannister's lid, put the tube through it and seal around the tube. When you put the lid back on, the tube should almost reach the bottom of the cannister, but not quite.

There are three ways to make the hole:

Drill really carefully: use a small sharp blade to drill a perfectly circular hole, stopping frequently to try the tube through it. When you can just get the tube through, stop drilling.

Drill quickly: use whatever tool you have handy - pocketknife, scissors, particle-beam accelerator - and then seal any gaps between the hole and the tube with blu-tac, modelling clay or hot-glue.

Melt it: heat a narrow nail in a flame (hold the nail with pliers or you'll burn yourself), and poke a hole in the middle of the lid. Quickly push the tube through the hole and, as the plastic cools, it will set and make an air-tight seal around the tube.


Did you push the tube too far through before you sealed it, and now you can't close the lid? Never mind, just snip the bottom of the tube off, no big deal.

Step 3: Fill It.

Fill the cannister about a third or half-full with coloured water and push the lid on.

Be careful, because the water can easily squirt out the top of the tube.

You should end up with the coloured water part-way up the tube with plenty of free space above it.

Step 4: Try It.

That, basically, is that. The thermometer is finished and works.

Hold the cannister in your fist - the warmth of your hand will make the air in the cannister expand and push the water up the tube. Dip it in your coffee, it will go up further. Stand it in your fridge and the air will cool and contract, pulling the water back down.

Obviously you cannot use the thermometer to check your freezer compartment or your sauna (think about it...), but you are now the proud possessor of a working model of an early Fahrenheit thermometer.

Step 5: Calibrate It.

Thermometers aren't much use without a scale. You can have one as well.

Tape the card against the tube like a flag, then hold the cannister in your fist. When the water stops moving, mark the point and label it "hand heat". Try a range of other places - a cup tea just cool enough to drink, slip it under the quilt with your loved one in the morning. One of Fahrenheit's original standard points was "human armpit".

When you have enough points on your scale, add some numbers. It doesn't really matter what they are, either, since Fahrenheit's scale was quite arbitrary - he just used numbers that "felt" right, which is why water freezes at 32F and boils at 212F.

Give your scale a name, then take delight in confusing your friends when the conversation inevitably drifts round to the weather;

"Boy, it's hot today!"
"Yeh, it was nearly forty Desmonds when I checked this morning."



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55 Discussions

argha halderKiteman

Reply 5 years ago on Introduction

every day i search your name in the search bar and see some awesome instructables everytime!and keep commenting on them.hope many such instructables from you.(and keep replying to my comments and question. just saying!)


12 years ago

It might just be a rumor, but I heard the Fahrenheit scale isn't totally arbitrary, 0 degrees is supposed to be the coldest temperature you can achieve with salt and ice, and 100 is supposed to be body temperature. He was a little off, but there was still method to his madness.

4 replies

Reply 12 years ago

I thought it was defined a bit more wackily... 99 is body temperature I thought? But I remember he defined 100 to be like, the temperature cow's milk comes out as or something... It's definitely defined along those lines


Reply 12 years ago

Sort of. 0 was the coldest he could get fluid water with salt. 100 was supposed to be body temperature, but the subject he used, his wife, had a slight fever when he established the measure. Or so the story goes...


8 years ago on Introduction

Some people* still use the scale he developed; the Fahrenheit Scale.

*like Americans (me!)  :D


10 years ago on Introduction

BTW: This thing is called a thermo"meter", not a "thermofahren" or a thermo"reaumur". It's a metric's, metric's world. BSG Which number had the space mission that's crashed 'cause US-nerds did not not notice that their european colleagues calculated in metrics and not in feet?

2 replies

Reply 10 years ago on Introduction

Sorry, you're wrong there. The word "thermometer" means "heat measurer". A "meter" is a device for measuring. A "metre" is a unit of length.


Reply 8 years ago on Introduction

I hate it when people make an almost perfect correction, and then mess it up at the end: Meter is the [chiefly] American spelling for metre. Similarly, center for centre, liter for litre, etc. But yes, thermometer comes ultimately from the Greek thermos and metron, heat measurer.


9 years ago on Introduction

What is with science teachers, Brits and biros... Biros are exactly the definition our science teacher uses for pens.

1 reply