Red thermometers are alcohol, with a dye. Invented in the 1600's. They're far less toxic or dangerous than the mercury thermometers (mercury is silver) if broken. However, they are more difficult to make, as they require a thinner capillary tube for the alcohol.
The question implies that a thermometer might be both red, and silver -- this does not seem likely. Perhaps the question needs to be re-asked in a way that is more specific. Just what is red outside, but silver inside? Do you mean that a red thermometer broke and somehow it now looks silver inside (which might happen once the alcohol has evaporated away)? Or do you mean that the writing on the outside of a thermometer is red but there is a column of silver (mercury) inside?
The question implies that a thermometer might be both red, and silver -- this does not seem likely. Perhaps the question needs to be re-asked in a way that is more specific. Just what is red outside, but silver inside? Do you mean that a red thermometer broke and somehow it now looks silver inside (which might happen once the alcohol has evaporated away)? Or do you mean that the writing on the outside of a thermometer is red but there is a column of silver (mercury) inside?
