The bulk update request #10521 has been approved by @NWF_Renim.
create alias mercury_thermometer -> liquid-in-glass_thermometer
Mercury thermometers are a type of liquid-in-glass thermometer, and the tag is mostly being used for non-mercury thermometers (ex: post #4543260, post #3836605, post #3810302). The stereotypical red liquid thermometers use a liquid, such as alcohol, with a dye to make it standout. If it was mercury or another metal, then the liquid filling would generally be a greyish/silvery metallic color.