Beckmann-Thermometer

The Beckmann thermometer (after Ernst Otto Beckmann 1905) is a special design of a mercury thermometer.

It allows the measurement of temperature difference at a resolution of 0.01 ° C. This is achieved by using a very fine mercury capillaries. The disadvantage of the Beckmann thermometer is that due to the large spreading of the temperature range (1 ° C corresponds to a column of mercury of about 5 cm in length) of the total measurement range is small, about 5 ° C ( ie at 0 ... 100 ° C represent to can, the thermometer should be 5 m long).

The high spreading is achieved in that the thermometer is set waiving an adjusted starting point to the required measuring range. For this purpose, the amount of mercury in the capillary can be manually adjusted so that the mercury level is for the region of interest within the scale - its setting requires a certain minimum level of skill.

In order for the Beckmann thermometer can only measure temperature changes, but no temperature yourself. Use it used to be for the exact determination of melting point and boiling point changes and also to determine the molar mass using the cryoscopic method, now use it mainly still students in basic practical physical chemistry.

The price of a Beckmann thermometer is about 150 euros. There are electronic devices that provide the same resolution and are more expensive, but have the advantage of providing absolute temperatures (e.g. Pt100 resistance thermometer) today.