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I'd like to accurately calibrate a digital thermometer I'm building in the range of $50^\circ$ to $120^\circ$ Celsius.

I'm aware that one can buy various chemicals that have melting points in this range, but are there any readily available household / pharmaceutical items I could use instead?

From what I have read, it looks like the two easiest candidates would be vanillin or Sodium acetate (Thanks Curt F.), but I'm not sure how one would go about creating a pure enough calibration standard at home.

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    $\begingroup$ The boiling point of water is a good calibration point. Sodium acetate trihydrate has a well-known melting point at 58 °C but I don't know if you count that as "household". $\endgroup$ – Curt F. Apr 13 '15 at 4:55
  • $\begingroup$ @CurtF. So one would just boil vinegar and baking soda, then cool and reheat to find the melting point? That sounds pretty household to me. $\endgroup$ – nbubis Apr 13 '15 at 8:29
  • $\begingroup$ Related: Looking for a chemical to calibrate a temperature sensor $\endgroup$ – Loong Apr 13 '15 at 8:56
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    $\begingroup$ nubis: true but (i) it would take a lot of boiling and (ii) I worry about purity. Without perfectly pure compounds, the melting point is not exact. $\endgroup$ – Curt F. Apr 13 '15 at 14:54
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According to this cooking site, Crisco brand vegetable shortening melts between $\mathrm{47^oC-48^oC}$ (yes, I know $\mathrm{48^oC}$ is less than $\mathrm{50^oC}$, but it seems pretty close to me). The best way to use such a non-certified melting point "standard" like this is to use your thermometer side-by-side with a properly calibrated thermometer.

Vanillin may be your best bet (melting point of $\mathrm{81^oC - 83^oC}$). Again, using a calibrated thermometer to check the actual melting point would be the ideal situation.

Although your question asks about calibrating based on melting point measurements of household items, household items just aren't usually of the purity required for accurate melting point based thermometer calibration. In the absence of a calibrated thermometer as discussed above, the best way to calibrate your thermometer is probably to use the freezing and boiling points of water (don't forget to adjust boiling point for altitude if you don't live at sea level), then check the melting points of Crisco and vanillin if you want. Good agreement with these stated melting points would be a good indicator of proper thermometer calibration, while poor agreement could either be due to improper thermometer calibration or impure material.

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