# Why should an ethanol-filled thermometer NOT be used at temperatures close to 100 ""^@C?

Mar 24, 2016

The alcohol-filled thermometer will be off the scale when the temperature is $230$ ""^@F.
The boiling point of ethanol is $+ 78$ ""^@C. This limits the top measurement of the thermometer to this temperature. Of course, the MELTING POINT of ethanol is $- 100$ ""^@C or so, which allows measurement of temperatures lower than $0$ ""^@C.
A thermometer may be filled with mercury, or (for lower temperatures), it may be filled with ethyl alcohol, toluene, xylenes, or some liquid whose melting point/boiling point extends the range of measurement. Because (as far as I know) the rate of liquid expansion when heated gives a LINEAR SCALE, the thermometer may be calibrated by placing in an ice bath (or a colder bath), marking off this freezing point, then placing in a bath of boiling water, and marking off this boiling point at $100$ ""^@C. The THINNER the glass capillary, the greater the distance between the two points and the more accurate the reading on the thermometer.