How does this thermometer work?

i have this kid bathtub that had a thermometer inside, it's not digital or electric, it's round. my kid was playing with it and took it apart (so my husband tells me, i wasn't around). so today i took a look at it to check it out, and to see if there was any mercury, since i was worried about it, but there didn't seem to be any? or anywhere to keep it anyway. there is just a round space with a paper with the degrees (that i threw out) and in the middle a little black thing where the hand was that indicated the degree.
i am still a bit worried, should i be? we keep the tub in the regular bathtub so it gets washed out all the time.
but i'm also wondering how it works otherwise. i have no clue if it was accurate, i never paid attention to it, although the hand would move around.

Ray;mond2013-10-17T07:12:54Z

Favorite Answer

That is a good answer. It likely has a metal strip wound in a coil with the hand connected to the center end of the metal strip. This called a bimetal strip = two metals welded to each other so as to double the thickness of the strip. They can be calibrated plus or minus about one degree, but require frequent recalibration to remain that accurate. Toxicity hazard is low, even if one of the metals is an alloy of copper and beryllium.

Zardoz2013-10-17T07:08:38Z

More than likely a bimetallic strip. Two different metal strips are bonded together. One metal expands more with temperature than the other. This causes the strip to bend. The bending of the strip causes a pointer to move relative to the scale.