Apparatus for comparing airs, 1761.
© Science Museum / Science & Society Picture Library
George Adams, instrument maker to the king, who made this, called this 'a convenient apparatus to examine a portion of air, taken by chance or choice either in the atmosphere or in a place filled with vapours or known exhalations'. The apparatus fitted on the air pump. Vapours from burning matter for example, filled the large receiver on the right. The glas sphere on the left provided clean dry air from the atmosphere. Operating the pump sucked the two airs into the central jars where they could be compared.