Resistance thermometer: Iron coil in liquid Nitrogen and flame varies current.

Resistance thermometer: Iron coil in LN2 and flame varies current. A 6 volt battery sends about 2.5 amps through an iron coil (1.8 at room temperature). If the coil is heated with a bunsen burner flame, the resistance rises, and the current falls. If the coil is submersed in liquid nitrogen, the resistance falls, and the current rises dramatically.
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The length of the section of the long coil that is heated or cooled can be adjusted (e.g., place deeper into LN2). Tossing a little LN2 to cool the full wire gives readily noticeable increase I (projected). Illustrated resistors in series since hot/cold parts have different R. Put R at room temperature on board, and hot/cold R to anticipate size of effect.