Not to mention, with all of magic and all of physics to work with, you'd really think there'd be something with a measurable linear dependence on temperature that was not the volume of mercury.  Like seriously.  Maybe he can build a resistance thermometer and calibrate it off a mercury one?  Though resistance thermometers probably don't work at, like, another ten times the temperature distance between frozen water and boiling water, such as you need for metallurgy... actually, Keltham would be sort of surprised if the Element-80 thermometers worked for that either.

Not to mention, with all of magic and all of physics to work with, you'd really think there'd be something with a measurable linear dependence on temperature that was not 'the density of mercury'.  Like seriously.  Maybe he can build a resistance thermometer and calibrate it off a mercury one?  Though resistance thermometers probably don't work at, like, another ten times the temperature distance between frozen water and boiling water, such as you need for metallurgy... actually, Keltham would be sort of surprised if the Element-80 thermometers worked for that either.