The eudiometer is a glass instrument used to measure gas volume changes and was first used to measure oxygen in the atmosphere. It is usually a graduated cylinder shape and can be immersed in water or mercury. The term comes from Greco-Roman origin and the first mention dates back to 1777. Joseph Priestley used a similar tool to discover gases before the eudiometer was invented.
An eudiometer is an instrument used to measure the volume change of gases. The first incarnations were intended to measure the amount of oxygen in the atmosphere. Made of glass, the eudiometer typically has an elongated tube shape with a measuring scale, similar to a barometer or thermometer.
Each eudiometer has one end closed, with the other end open for water filling. It is usually immersed in a container of water, closed end up. When immersion occurs, a sample of gas enters the instrument. This creates an electric spark between the two sealed wires in the eudiometer and allows for a graduation inside to measure the change in gas volume. Some instrument users rely on mercury for immersion rather than water.
The eudiometer is most commonly manufactured as a graduated cylinder. This means it looks like a glass container with measurement marks on the sides. The eudiometer is usually available in measurement scale ranges of 50 to 100 milliliters (mL) or in grams. The graduated cylinder shape first came into use in the mid-20th century and has been the most popular type of eudiometer ever since.
Although the tall, narrow cylinder is the most common shape, the eudiometer is available in other shapes. Some are U-shaped, with one end slightly longer than the other. There are also T-shaped cylinders, characterized by small truncated arms.
The term “eudiometer” is of Greco-Roman origin. “Eu” means “good” and “god” means God. The last part is a reference to God’s residence as in the atmosphere, in the heavens or in the sky. The “meter” part indicates the measurement.
The first mention of an eudiometer dates back to 1777, when the Italian physicist Alessandro Volta wrote in his letters about a laboratory device capable of measuring air quality. The instrument’s invention, however, is often credited to another Italian physicist, Marsilio Landriani, who described the instrument in an 1885 publication titled Physical research around the salubrity of the air. He theorized that air can be analyzed chemically and gases in the atmosphere can be isolated using a laboratory device.
Englishman Joseph Priestley preceded both men by using an instrument to discover gases such as ammonia, hydrochloric acid and oxygen. The tool he used, however, has been described as a pneumatic trough.
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