|Gordon van Wylen's 1959 Fundamentals of Classical Thermodynamics, having gone through three editions (1985). |
The term classical thermodynamics seems to have an elusive coinage history. According to one account, it was German physicist Georg Helm who wrote the first section devoted to a discussion on the use of the term 'classical'.  Specifically, in his 1898 Historical Development of Energetics, Helm was said to have included a section on “Classical Thermodynamics”, arguing to the effect that thermodynamics had reached such a well-established state that “it can certainly be called ‘classical’”, hence the name classical thermodynamics. Helm, supposedly, comments, however, that the label ‘classical’ had first been used not by him but by those who opposed all efforts to develop thermodynamics further. 
Yet, according to the 1905 views of American physicist Edgar Buckingham, the term 'classical thermodynamics' had been introduced by French physicist Pierre Duhem, a noted student of German physical chemist and energetics founder Wilhelm Ostwald. In Buckingham’s own words: 
“Aside from these three difficulties [(a) the definition of temperature; (b) the definition of quantity of heat; and (c) the statement of the theorem of Clausius for irreversible processes], the rest of ‘classical thermodynamics’, as Pierre Duhem has named it, seems to be a fairly logical and satisfactory whole.”
American physicist Paul Epstein, in his 1937 Textbook of Thermodynamics, states that “the writings of the classical period culminated in German physicist Max Planck’s ‘Lectures on Thermodynamics’.”  Epstein, however, does not specify which lectures of Planck to which he refers. It is probable that he referring to Planck’s famous series of eight lectures delivered at Columbia University in 1909, most of which were on thermodynamics. 
Most-notably, in a general sense, the phrase “classical thermodynamics” seems to have drifted into lay science folklore in the following circa 1940s quote by German-born American physicist Albert Einstein: 
“A theory is the more impressive the greater the simplicity of its premises, the more different kinds of things it relates, and the more extended its area of applicability. Therefore the deep impression that classical thermodynamics made upon me. It is the only physical theory of universal content which I am convinced will never be overthrown, within the framework of applicability of its basic concepts.”
In the years to follow, and specifically in the 1950s, a number of books and textbooks began to appear with this title, a trend that continued into the 1970s.  The term “classical thermodynamics”, as used by Einstein, as judged by his first 30 published scientific papers (85% of which were in thermodynamics), would seem to refer generally to the thermodynamic publications of German physicist Rudolf Clausius, and those surrounding or connected to his work. 
In the 1957 publication Elements of Classical Thermodynamics, British physicist Brian Pippard defined classical thermodynamics as “the method of approach that takes no account of the atomic constitution of matter [and] makes no attempt to provide a mechanistic explanation of why a given substance has the properties observed experimentally.”  This would generally date classical thermodynamics to the publication up until the year 1889 or the years before the thermodynamic publications of German physicist Max Planck and his theory of energy quanta in black bodies.
1. McQuarrie, Donald. A. and Simon, John D. (1999). Molecular Thermodynamics (keyword: classical thermodynamics, pgs. 1-2). University Science Books.
2. (a) Einstein, Albert. (author), Paul Arthur, Schilpp (editor). (1979). Autobiographical Notes. A Centennial Edition, (p. 31). Open Court Publishing Company. (b) As quoted by Don Howard, John Stachel. Einstein: The Formative Years, 1879-1909 (Einstein Studies, vol. 8). Birkhäuser Boston. 2000. (p. 1).
3. (a) Buchdahl, Hans A. (1966). The Concepts of Classical Thermodynamics. Cambridge University Press.
(b) Münster, Arnold. (1970). Classical Thermodynamics. Wiley-Interscience.
4. List of Scientific Publications by Albert Einstein – Wikipedia.
5. Pippard, A. Brian. (1957). Elements of Classical Thermodynamics for Students of Physics (pg. 1). Cambridge University Press.
6. Buckingham, Edgar. (1905). “On Certain Difficulties which are Encountered in the Study of Thermodynamics”, (classical thermodynamics, pg. 208), Philosophical Magazine: a Journal of Theoretical, Experimental, and Applied Physics, pgs. 208-13. Taylor & Francis.
7. Van Wylen, Gordon J. and Sonntag, Richard E. (1976). Fundamentals of Classical Thermodynamics. Wiley.
8. Epstein, Paul. (1937). Textbook of Thermodynamics (pg. vii). John Wiley & Sons.
9. Planck, Max. (1909). Eight Lectures on Theoretical Physics (1: Reversibility and Irreversibility, pgs. 1-20; 2: Thermodynamic States of Equilibrium in Dilute Solutions, pgs. 21-40; 3: Atomic Theory of Matter, pgs. 41-57; 4: Equation of State for a Monoatomic Gas, pgs. 58-69; 5: Heat Radiation: Electrodynamic Theory, pgs. 70-86; 6: Heat Radiation: Statistical Theory, pgs. 87-96; 7: General Dynamics: Principle of Least Action, pgs. 97-111; 8: General Dynamics: Principle of Relativity, pgs. 112-). (Trans. A.P. Wills.). BiblioBazaar, 2009.
10. Staley, Richard. (2008). Einstein’s Generation: the Origins of Relativity Revolution (Georg Helm and classical thermodynamics, pg. 355-57). University of Chicago Press.
11. (a) Helm, Georg F. (1898). Die Energetik: Nach Ihrer Geschichtlichen Entwickelung (Energetics: Historical Development). Leipzig.
(b) Helm, Georg F. (2000). The Historical Development of Energetics (classical thermodynamics, pg. 153-60). Kluwer Academic Press.
● Classical thermodynamics – Wikipedia.