# Z

The letter Z, the twenty-sixth letter of the 26-letter English alphabet, derived from the Phoenician "zayin" symbol. [1]

In symbols, Z, twenty-sixth letter of the 26th letter English alphabet, is the symbol for []

## Mathematics

In mathematics, "z", lower case, is the symbol for the vertical axis in the Cartesian coordinate system.

## Thermodynamics

In 1875, Rudolf Clausius employed upper “Z” and lower case “z” in his derivation of the forces involved in the work function of a moving body: [2]

${\displaystyle F(xyz)=const}$

In words:

“W is the work done whenever a body moves under the influence of a force. The product of the force and distance moved through is the mechanical work which the force performs during the motion.”
— Rudolf Clausius (1875), The Mechanical Theory of Heat (§: Mathematical Introduction)

In 1924, James Partington, was employing the symbol "Z" thusly: “Z is called the thermodynamic potential by analogy with the potential function in dynamics: ϕ1 – ϕ2 = work”, was employed as the symbol for the isothermal-isobaric thermodynamics potential: [1]

${\displaystyle U-TS+pV}$

In other words, Z, at one point was a symbol for the Gibbs energy, in modern parlance. [3]

The letter “Z” is also sometimes employed as the “compressibility factory” of a gas (see: characteristic function notation table). [4]

## References

1. Thims, Libb. (2020). Human Chemical Thermodynamics — Chemical Thermodynamics Applied to the Humanities: Meaning, Morality, Purpose; Sociology, Economics, Ecology; History, Philosophy, Government, Anthropology, Politics, Business, Jurisprudence; Religion, Relationships, Warfare, and Love (§2: Alphabet) (pdf). Publisher.
2. (a) Symbols (EoHT.info) -- Hmolpedia 2020.
(b) Symbols – EoHT.info | Internet Archive (21 Feb 2020).
3. Partington, James. (1924). Chemical Thermodynamics: An Introduction to General Thermodynamics and its Applications to Chemistry. D. Van Nostrand.
4. Compressibility factor – Wikipedia.