Beckmann Thermometer

a mercury thermometer with an enclosed scale that is used to measure small temperature differences. It was invented by the German chemist E. O. Beckmann in 1888.

The main scale of a Beckmann thermometer usually covers 3° to 5°C and has divisions of 0.02°C, 0.01°C, and even 0.005°C. The range of temperatures measured with such a thermometer is determined by the amount of mercury in the reservoir and capillary of the thermometer. The mercury in the reservoir can be partially drawn off into an auxiliary chamber, which is equipped with a secondary scale for the entire range of use of the thermometer and has divisions of 1° or 2°C. Before use, the mercury in the chamber is adjusted on the scale to the maximum mark of the temperature range to be measured and is separated from the mercury in the capillary and the reservoir by shaking, thus readying the thermometer. The accuracy of the readings is usually 0.002°C. Beckmann thermometers are used in laboratory practice for calorimetry and for measurements near phase transition points, but their use is decreasing.