Eudiometer

Eudiometer

Closed end of a eudiometer
Uses	Gas volume measurement
Notable experiments	Composition of water
Inventor	Marsilio Landriani
Related items	Barometer Burette

A eudiometer is a laboratory device that measures the change in volume of a gas mixture following a physical or chemical change.

Depending on the reaction being measured, the device can take a variety of forms. In general, it is similar to a graduated cylinder, and is most commonly found in two sizes: 50 mL and 100 mL. It is closed at the top end with the bottom end immersed in water or mercury. The liquid traps a sample of gas in the cylinder, and the graduation allows the volume of the gas to be measured. For some reactions, two platinum wires (chosen for their non-reactivity) are placed in the sealed end so an electric spark can be created between them. The electric spark can initiate a reaction in the gas mixture and the graduation on the cylinder can be read to determine the change in volume resulting from the reaction. The use of the device is quite similar to the original barometer, except that the gas inside displaces some of the liquid that is used.

In 1772, Joseph Priestley began experimenting with different “airs” using his own redesigned pneumatic trough in which mercury instead of water would trap gases that were usually soluble in water. From these experiments Priestley is credited with discovering many new gases such as oxygen, hydrogen chloride, and ammonia. He also discovered a way to find the purity or “goodness” of air using “nitrous air test”. This test was conducted by mixing nitrous gas with a test sample of another gas and trapping it in the pneumatic trough, essentially the greater the decrease in volume, the more pure the sample of gas was (key principle in eudiometry). Henry Cavendish later used a similar device to determine the fraction of oxygen in the Earth's atmosphere.

It is from these experiments that Marsilio Landriani became inspired to create a more useful tool in measuring the “healthiness” of air. In 1775, Landriani invented the first eudiometer and used it to conduct his own experiments. From these experiments Landriani theorized about the temperament of certain gases and the atmosphere and later published a paper called Ricerche fisiche intorno alla salubrità dell'aria (Physical researches on the salubrity of air). Though many of his findings were incorrect, his invention was the building block for the modern day eudiometer.