Perfect gas

In thermodynamics, perfect gas is a substance, in the gaseous state, in such a condition that the total pressure exerted by any number of portions of it, at a given temperature, against the sides of a vessel in which they are enclosed, is the sum of the pressures which each portion would exert if enclosed in the vessel separately at the same temperature. [1] The term perfect gas is a synonym of more modern term "ideal gas".

Etymology
The term "perfect gas", as defined above in 1859 by Scottish engineer William Rankine, traces to the use of the word “perfect” in descriptions of earlier 17th century attempts to make a perfect vacuum, such as discussed in the works of Denis Papin, by the ignition or explosion of a substance inside of a piston and cylinder. In this sense, the word “perfect” means that the cylinder had been made perfectly empty of atoms or gas particles. In 1890, the phrase “ideal perfect gas” was being used in relation to gases that obeyed the laws of Charles and Boyle. In 1923, phrases such as “perfect gas or ideal gas” were being used. Soon thereafter, the adjective “perfect” tended to be removed, leaving the term ideal gas in common use.

References
1. Rankine, William. (1859). A Manual of the Steam Engine and Other Prime Movers, (pg. 226, chapter III: “Principles of Thermodynamics”, pgs. 299-478). London: Charles Griffin and Co.

Further reading
‚óŹ Clausius, Rudolf. (1879). The Mechanical Theory of Heat, (ch. II: On Perfect Gases, pgs. 39-68). London: Macmillan & Co.

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