Chemistry and the Law

by Harold Goldwhite

April, like most months, is rich in anniversaries of scientists who made major contributions to chemical sciences. Among them are James Watson, Robert Woodward, Carl Lindemann, and Glen Seaborg. But I choose to discuss the career of a great physicist whose work made such an impact on our science that it changed the thinking and work of every chemist who followed him. I refer to Max Karl Ernst Ludvig Planck, born in Kiel, Germany, on April 23 (a birthday he shares with Shakespeare), 1858.

The Planck family had, in common with the family of J. Clerk Maxwell, a long history of public service as lawyers, scholars, and clergymen. Planck’s father was a professor of law. The family moved from Kiel to the independent state of Bavaria when Max was 9 years old. He attended the Maximilian Gymnasium in Munich, where he chose an emphasis on physics over music (he remained an excellent pianist all his life), perhaps through the influence of his physics teacher H. Muller. His experience for his first 3 years at the University of Munich was less inspiring, and he transferred to Berlin, where he encountered two distinguished physicists as teachers. Kirchhoff, the collaborator of Bunsen in spectral analysis, apparently delivered his polished lectures in such a manner as to put many in his audience to sleep. Helmholz, the great expert on electrical and optical phenomena, was often unprepared and difficult to follow.

Planck read widely in physics and decided to specialize in thermodynamics, after reading some of Clausius’s work. His doctoral thesis, which included a critique of Clausius’s views on irreversibility, was successfully submitted to the University of Munich in May 1879. It is worth noting that some of Planck’s results had already been published by J. Willard Gibbs in a very long article published in the somewhat obscure Transactions of the Connecticut Academy of Sciences, an article that was not brought to the attention of the European thermodynamicists for decades. On the strength of his thesis, Planck was appointed Privat-Dozent at Munich and then in 1885 was called to Kiel as Extraordinary Professor of Theoretical Physics.

In 1889, on the death of Kirchhoff, the prestigious University of Berlin asked Boltzmann to succeed him. Initially, he accepted, but then changed his mind. In his place, the somewhat unlikely choice was the young 34-year-old Planck, who was appointed Professor in 1892, becoming a colleague of the great Helmholz. Planck remained at Berlin for the rest of his professional career, retiring in 1928. His successor was Schroedinger.

Planck’s work before he ascended to the Berlin Chair was collected in his important thermodynamics text, published in 1897, and included discussion of chemical potentials and their applicability to equilibrium constants; dissociation of real gases; and the thermodynamics of colligative properties, including freezing-point depression and osmotic pressure. These treatments of really fundamental chemical and physical problems led him to the forefront of classical thermodynamics.

At Berlin, he began to turn his attention to emissivity phenomena, the so-called black-body radiation. His predecessor, Kirchhoff, had provided theoretical backing for the observations that the distribution of radiant energy with wavelength (or frequency!) emitted from a heated enclosure did not depend on the material of the enclosure. It was therefore a quite general or universal result. In 1893, Wien had used experimental data to derive his displacement law, which connected the enclosure temperature with the frequency of maximum energy output. The efforts of some of the best physicists of the day, including Rayleigh and Jeans, were able to explain parts of the Wien law at low frequencies and high temperatures, but failed at other extremes. The field was open for Planck’s efforts.

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