Dalton's eudiometer, 2000

Museum of Science and Industry, Manchester, England. Eudiometer owned by John Dalton. This is of the design of Henry Cavendish and is used to test the "goodness" of air, its proportion of oxygen. The air to be tested is collected in the eudiometer over water, with the top end of the eudiometer capped (and fitted with electrodes) and the bottom end immersed in water. A small quantity of hydrogen gas is added to the trapped air, and ignited with a spark through the electrodes. The amount by which the water rises in the tube indicates the "goodness" of the trapped air.