Beckmann thermometer
The Beckmann thermometer (after Ernst Otto Beckmann 1905) is a special design of a mercury thermometer .
It enables the measurement of temperature differences with a resolution of 0.01 ° C. This is achieved by using a particularly fine mercury capillary . The disadvantage of the Beckmann thermometer is that due to the wide spread of the temperature range (1 ° C corresponds to a mercury thread approx. 5 cm long), the total measuring range is small, around 5 ° C (i.e. in order to be able to display 0 ... 100 ° C) the thermometer should be 5 m long).
The wide spread is achieved by setting the thermometer to the required measuring range without using an adjusted starting point . To do this, the amount of mercury in the capillary can be set by hand so that the mercury level for the area of interest lies within the scale - setting it requires a certain minimum of skill.
The Beckmann thermometer can only measure temperature changes, but not the temperature itself. In the past it was used for the precise determination of melting point and boiling point changes and also for determining the molar mass with the aid of cryoscopy . Today it is mainly used by students in the basic practical course in physical chemistry.
The price for a Beckmann thermometer is around 150 euros. There are electronic devices today, achieve the same resolution, cost less mechanically stable, are smaller and lighter and have the added advantage of providing absolute temperatures (eg. Pt100 - resistance thermometers ).
Individual evidence
- ↑ Ernst Beckmann: Modification of the thermometer for the determination of molecular weights and small temperature differences . In: Journal of physical chemistry . 51, 1905, pp. 329-343. , ISSN 0942-9352
- ↑ G. Amarell: Molecular weight determination with the Beckmann thermometer . In: GIT Labor-Fachzeitschrift , Vol. 5 (1961), special issue October, ISSN 0016-3538