MOLLIER, RICHARD

(b. Trieste, 30 November 1863; d. Dresden, Germany, 13 March 1935)

thermodynamics.

Mollier was the eldest son of German parents. His father, Eduard Mollier, a Rhinelander, was a naval engineer at, and later director of, a Trieste machine factory; his mother (née von Dyck) was a native of Munich. After graduating summa cum laude (1882) from the local German Gymnasium, Mollier studied mathematics and physics at the universities of Graz and Munich. He soon transferred to the Technische Hochschule of Munich, where Moritz Schröter and Carl von Linde became his most influential teachers. He graduated in 1888 and, after a brief engineering practice at his father’s factory in Trieste, became Schrötefs assistant in 1890. His first scientific investigations were his Habilitation thesis on thermal diagrams in the theory of machines (1892) and his doctoral dissertation at the University of Munich on the entropy of vapors (1895). In 1896 Felix Klein, who was conducting a wide-ranging campaign to reunite science and technology, called Mollier to the University of Göttingen to introduce “technical physics” into the curriculum. Mollier’s stay was brief. Feeling isolated in a purely scientific atmosphere, he was delighted to answer an invitation in 1897 to succeed Gustav Zeuner at the Technische Hoetachule of Dresden. In this post, as professor of the theory of machines and director of the machine laboratory, Mollier spent his working life. He subsequently received international recognition for his contributions to thermodynamics, as well as the concomitant honors.

Mollier was unassuming and kindly, if somewhat retiring, and he took his teaching duties seriously. His lectures, prepared by a unique method, were much praised. Using no notes, he would compose and memorize them, so that clarity of organization and simplicity of style were combined with spontaneity. Several of his pupils became notable contributors to thermodynamics, including F. Bošnjaković, F. Merkel, Wilhelm Nusselt. and Rudolf Plank—as well as his own sister Hilde Mollier, who later married the electronics pioneer H. G. Barkhausen.

Although his engineering colleagues considered Mollier a pure theoretician instead of experimenting himself, he based his findings upon the empirical data of others—his role was actually that of a mediator between the theoretical work of Clausius and J. W. Gibbs (whose work he knew through Ostwald’s 1892 German translation) and the realm of practical engineering. From the beginning his interest centered on the properties of thermodynamic media and their effective presentation in the form of charts and diagrams. It was here that he made his crucial contribution. Engineers had traditionally visualized thermodynamic processes in terms of the pressure-volume (P-V) diagram with which they were familiar from practical experience with the steam engine indicator. This diagram, however, obscured the significance of the second law of thermodynamics. In 1873 Gibbs had suggested an alternative in the temperature-entropy (T-S) diagram where Carnot processes stand out as simple rectangles, and the degree of approximation of actual thermodynamic processes to ideal ones can be easily judged. It was at this point that Mollier introduced the concept of enthalpy, a property of state that was then little known (1902). This property had been defined in 1875 by Gibbs, under the name “heat function for constant pressure,” as the sum of internal energy and of the product of pressure and volume (the term “enthalpy” was coined later by Kamerlingh Onnes). Like Clausius’ entropy, enthalpy is an abstract property that cannot be measured directly. Its great advantage is that it describes energy changes in thermodynamic systems without requiring a distinction between heat and work. Employing this new property of state, in 1904 Mollier devised an enthalpy-entropy (H-S) diagram, which retained most of the advantages of the T-S diagram, while acquiring some additional ones. While vertical lines signified, as before, reversible processes, horizontal lines in it described processes of constant energy; the diagram thus demonstrated in strikingly simple fashion the essence of both the first and the second law of thermodynamics. Quantities of work, which in the P-V and the T-S diagrams had appeared as an area, as well as discharge velocities through adiabatic nozzles, were represented here simply as vertical distances. Although the H-S diagram quickly became a principal tool of power and refrigeration engineers, to Mollier it was merely an element in a broad reorganization of thermodynamic practice. He also developed a new system of thermodynamic computation in which enthalpy played an important role, and as a basis for such calculations he published charts and diagrams of the properties of steam and of various refrigerants (his steam tables, first published in 1906, quickly went through seven editions). Besides the H-S diagram he proposed a number of other enthalpy diagrams, which have all become known, upon recommendation of the U.S. Bureau of Standards in 1923, as Mollier diagrams.

Mollier also contributed to other areas of thermodynamics. In 1897 he published an important study on heat transfer, before turning this subject over to his pupil Wilhelm Nusselt, who soon made fundamental contributions to it. His presentation of the first mathematical analysis of the process of combustion (1921) has proven of lasting utility.

BIBLIOGRAPHY

I. Original Works. Except for the chapter “Wärme,” in Akademischer Verein Hütte, Hütte: Des Ingenieurs Taschenbuch, 18th ed. (Berlin, 1902), and Neue Tabellen und Diagramme für Wasserdampf (Berlin, 1906; 7th ed., 1932), Mollier’s publications were confined to journals. His most important research papers are “Über die kalorischen Eigenschaften der Kohlensäure und anderer technisch wichtiger Dämpfe,” in Zeitschrift für die gesamte Kälteindustire, 2 (1895), 66–70, 85–91; “Über die kalorischen Eigenschaften der Kohlcnsäure ausscrhalb des Sättigungsgebietes,” ibid., 3 (1896), 65–69, 90–92; “Über den Wärmedurchgang und die darauf bezüglichen Versuchsergebnisse,” in Zeitschrift des Vereins deutscher Ingenieure, 41 (1897), 153–162, 197–202; “Über die Beurteilung der Dampfmaschinen,” ibid., 42 (1898), 685–689; “Dampftafel für schweflige Säure,” in Zeitschrift für des gesamte Kälteindustrie, 10 (1903), 125–127; “Neue Diagramme zur technischen Wärmelehre,” in Zeitschrift des Vereins deutscher Ingenieure, 48 (1904), 271–275; “Gleichungen und Diagramme zu den Vorgängen im Gasgenerator,” ibid., 51 (1907), 532–536; “Die physikalischen Grundlagen der Kältetechnik,” in Zeitschrift für die gesamte Kälteindustrie, 16 (1909), 186–190; “Die tech nische Darstellung der Zustandsgleichungen,” in Physikalische Zeitschrift, 21 (1920), 457–463; “Die Gleichungen des Verbrennungsvorganges,” in Zeitschrift des Vereins deutscher Ingenieure, 65 (1921), 1095–1096; “Ein neues Diagramm für Gasluftgemische,” ibid., 67 (1923), 869–872; and “Das i/x-Diagramm für Dampfluftgemische,” ibid., 73 (1929), 1009–1013.

II. Secondary Literature. The following are particularly useful for biographical data: N. Elsner, “Richard Mollier als Mensch und Wissenschaftler,” in Wissenschaftliche Zeitschrift der Technischen Universität Dresden, 13 (1964), 1101–1103; Heinz Jungnickel, “Kältetechnik—Stand und Entwicklung,” ibid., 1105–1106; Walter Pauer, “Erinnerungen an Richard Mollier,” ibid., 1103–1104; and Rudolf Plank, “Richard Mollier zum 70. Geburtstag,” in Zeitschrift für die gesamte Kälteindustrie, 40 (1933), 165–167; and “Richard Mollier,” in Kaltetechnik, 15 (1963), 342–344. Poggendorff, VI, 1766; and VIIa, pt. 3, 342; gives a number of further references.

Otto Mayr