# Who came up with R for the universal gas constant?

I never did find an answer from professors, or even see an acknowledgement in textbooks, on why capital-letter-r is invariably used to represent the constant 0.08206 L-atm/mol-K seen in chemistry everywhere. The only variation I've seen is to use subscripts or overbars to denote incorporation of a particular circumstances.

• Try this che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/… "Why is the universal gas constant in PV = nRT represented by the letter R?" His answer: Clapeyron first used this, and proposes possible reasons why. – Gerald Edgar Dec 29 '18 at 16:06
• @GeraldEdgar Perhaps you could convert this into an answer, with the quote about the ratio and Regnault ? – Conifold Dec 30 '18 at 3:55

I quote from Ask the Historian "The Universal Gas Constant" by William B. Jensen, Department of Chemistry, University of Cincinnati, published in J. Chem. Educ., 2003, 80, 731-732

Question
Why is the universal gas constant in $$PV = nRT$$ represented by the letter $$R$$?
This is best answered by tracing the origins of the ideal gas law itself. One of the first persons to combine Boyle’s law (1662) relating volume and pressure and Gay-Lussac’s law (1802) relating volume and temperature in a single equation appears to have been the French engineer, Benoit-Paul Emile Clapeyron (1799- 1864). In his famous memoir of 1834 on the Carnot cycle, he wrote the combined equation as $$pv = R(267 + t) \tag{1}$$ where $$t$$ is the temperature in degrees centigrade.
Later versions of the law kept the letter $$R$$.
Later in the same reference, Jensen guesses why "$$R$$" was chosen by Clapeyron.
So why did Clapeyron choose the letter $$R$$ for the constant in his gas law? The fact is that he doesn’t explicitly tell us why and we are left with two speculative answers: (a) it was arbitrary or (b) it stood for ratio or one of its French equivalents: raison or rapport, since Clapeyron noted that the value of R for each gas was obtained by evaluating the constancy of the ratio $$pv/(267 + t)$$ over a range of pressures and temperatures, a point also emphasized by Clausius using the revised ratio $$pv/(273 + t)$$.