Mercury-in-glas thermometer, 18th century.
© Science Museum / Science & Society Picture Library
This mercury-in-glas thermometer was used in the demonstration in which sal ammoniac (ammonium chloride) was dropped in dilute sulphuric acid. The whole apparatus was in a receiver on the air pump with the air removed. This thermometer showed that the temperature of the 'Efervescence' given off during the reaction was lower than that of the surroundings. The thermometer is graduated from -20 to 210 Fahrenheit. The scale on the left of the tube is marked in 2 degree intervals, and the scale on the right is offset by a degree to enable the temperature to be estimated to the nearest degree. The instrument was made by George Adams, instrument maker to the king.