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Basic Thermometer

Difficulty Level: 1/5 very simple

Parts and Tools

  • 35mm Film canister with lid
  • 15cm long glass capillary tube
  • Glue gun and glue
  • Food colouring
  • Water
  • Drill and drill bit or bradawl
  • Permanent marker


This guide shows how to make a very simple thermometer. The finished model works like a real spirit thermometer with the water in the chamber expanding or contracting with temperature. This water then either rises or falls in the length of capillary tubing. Although this thermometer is not as accurate as a standard version, it does work well if calibrated properly and is effective over a wide range of temperatures.

Fig 1: Empty film canister
Fig 1: Empty film canister

Fig 1 shows the type of empty film canister required. Black plastic canisters work better than white ones as more thermal energy is absorbed by the black surface. The cap needs to be easily removable. If a film canister cannot be obtained, a small conical flask and bung may be used.

Fig 2: Cap of the canister with a hole drilled in the centre
Fig 2: Cap of the canister with a hole drilled in the centre

Fig 2 shows the cap of the canister with a hole drilled in the centre. This hole needs to be roughly the same size as the diameter of the capillary tube. The hole can either be drilled or made using a small bradawl. If making the hole by hand, ensure that the edges are clean and the hole is as circular as possible.

Fig 3: Capillary tube inserted into the lid hole
Fig 3: Capillary tube inserted into the lid hole

Fig 3 shows the capillary tube which has been inserted into the lid hole. Adjust this so that when the lid is placed on the can, the bottom of the tube sits about half way into the can. Use a glue gun to attach the tube to the lid, ensuring there are no gaps where air could get in. Glue each side and allow to cool.

Fig 4: Finished model
Fig 4: Finished model

Fig 4 shows the finished model. Add a small amount of food colouring to some water and fill the canister to the brim. Suck a small amount of the water into the capillary tube so that the level sits about halfway up the tube and replace the lid. With a little trial and error the water level should remain about halfway up the tube.

To calibrate the thermometer, leave it for an hour or two until the water in the canister is at room temperature. Take a standard thermometer and check the temperature. Draw a line on the simple thermometer with a permanent marker at the water level and in small figures write the temperature.

When the temperature changes, check and add another line. Work out where the increments between the two temperatures should go. These will be evenly spaced. Mark each increment and you should find that the thermometer is fairly accurate over a wide temperature range.


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