Beckmann thermometer

It was invented by Ernst Otto Beckmann (1853 – 1923), a German chemist, for his measurements of colligative properties in 1905.

The temperature scale typically covers about 5 °C and it is divided into hundredths of a degree.

The peculiarity of Beckmann's thermometer design is a reservoir (R on diagram) at the upper end of the tube, by means of which the quantity of mercury in the bulb can be increased or diminished so that the instrument can be set to measure temperature differences at either high or low temperature values.

In setting the thermometer, a sufficient amount of mercury must be left in the bulb and stem to give readings between the required temperatures.

First, the thermometer is inverted and gently tapped so that the mercury in the reservoir lodges in the bend (B) at the end of the stem.