Harkins, William Draper

(b. Titusville, Pennsylvania, 28 December 1873; d. Chicago, Illinois, 7 March 1951)

physical chemistry.

Harkins was the son of Nelson Goodrich Harkins, a pioneer in the Pennsylvania oil fields, and Sarah Eliza Draper. In 1900 he graduated from Stanford University with a B.A. in chemistry and immediately accepted a teaching position at the University of Montana, where he became a professor and chairman of the chemistry department. While associated with Montana, Harkins did graduate work at the University of Chicago (1901–1904) and at Stanford University (1905–1906). He received his Ph.D. from Stanford in 1907 and did postdoctoral study at the Technical University in Karlsruhe (1909) and at the Massachusetts Institute of Technology (1909–1910). In 1912 Harkins accepted an assistant professorship at the University of Chicago. He remained there for the rest of his life, becoming associate professor in 1914, professor in 1917, and the Andrew McLeish Distinguished Service Professor for 1935.

Among his many activities, Harkins acted as consultant to a number of private companies, the Chemical Warfare Service, and the National Defense Research Commission. From 1932 he was a member of the International Commission on Atoms. He also served as vice-president of the American Association for the Advancement of Science and was elected to the National Academy of Sciences. On 9 June 1905 Harkins married Anna Louise Hatheway, the head of the English department at Montana. They had two children, Henry Nelson, who became a surgeon, and Alice Marion, who achieved recognition as a singer.

While at Montana, Harkins published three papers on arsenic pollution in smelter smoke, in which he showed that a smelter stack spewed thirty tons per day of arsenic trioxide (and at least as much copper) over the surrounding twenty miles of pastureland. By bringing the arsenic level to 200–500 parts per million in fall grasses, this pollution killed many hundreds of sheep, horses, and cattle. Because Harkins’ detailed and complete studies (supported by the Anaconda Farmer’s Association) left no possible loopholes for dispute, he was recognized as an expert on smelter pollution and became a consultant to the Mountain Copper Company of California, the U. S. Department of Justice, and the Carnegie Institution.

At Chicago, Harkins began work on the structure and the reactions of atomic nuclei. The leading researchers in this newly developing science (Ernest Rutherford, Francis William Aston, Frederick Soddy, Patrick Maynard Stuart Blackett) were mostly in England and, except for T. W. Richards at Harvard, there had been little American involvement. In 1915 Harkins and E. D. Wilson published five important papers concerning the processes of building complex atomic nuclei from protons, deuterium, tritium nuclei, and α-particles. At this time the only nuclear reactions that had been studied were the decomposition reactions of radioactive nuclei, for which the Einstein equation relating mass and energy predicted the observed energies. With the Einstein equation Harkins showed the enormous energy produced in the nuclear fusion of hydrogen to produce helium, with the attendant. 77 percent loss of mass; he also identified this reaction as the source of stellar energy. Harkins termed the decrease in mass in nuclear synthesis “packing effect,” and showed it to be lower in complex nuclei of even atomic number (considered to be produced by condensation of α-particles) than in complex nuclei of odd atomic number (considered to be produced by condensation of a tritium or lithium nucleus with α-particles). This observation led Harkins to propose that the even-numbered elements are more stable and he demonstrated that they are the more plentiful in stars, in meteorites, and on earth. In 1919 Harkins’ conclusions were confirmed by Rutherford, who bombarded various atoms with α-particles and found that of the elements so bombarded, only the odd-numbered ones lost a proton.

The Harkins and E. D. Wilson theory of atom building (1915) predicted atomic weights near units based on 16.000 for oxygen; deviations for lithium, chlorine, and many other elements were considered evidence for isotopes not yet observed. Chlorine isotope separation by diffusion was attempted in 1916, but greater success was obtained with hydrochloric acid in 1919 when 10,000 liters were processed. In February 1920 at Cambridge, Aston announced evidence from mass spectroscopy for chlorine isotopes of mass 35 and 37, while in April 1920 Harkins published a preliminary report on his evidence for chlorine isotopes of 35, 37, and 39. Aston subsequently confirmed the prediction of chlorine-39. In 1921 Harkins showed that with the diffusion process he could obtain mass differences for hydrochloric acid of one part in 645. Subsequent studies with mercury diffusion demonstrated mass differences of 180 parts per million.

Rutherford carried out his 1919 studies (the first nuclear syntheses) in a spinthariscope, which could measure only the range of nuclear particles. Harkins realized that the C.T.R. Wilson cloud chamber could allow exact determination of the energy and mass of nuclear reactions and promptly analyzed tens of thousands of α-particle tracks in nitrogen, and argon by this method; he found (1923) that no collisions resulted in reactions. At Cambridge, Blackett used identical equipment and in 1925 found tracks to prove that nitrogen captured an α-particle and emitted a proton, thus synthesizing oxygen-17; Harkins confirmed this the following year.

A few months before Rutherford’s prediction, Harkins in 1920 predicted the existence of the neutron. But it was not until 1932 that the neutron was actually observed, by James Chadwick at Cambridge. Immediately after Chadwick’s discovery, Harkins, with David Gans and other co-workers, began investigations of nuclear reactions involving these particles. Chadwick and Rutherford contended that nuclear reactions initiated by bombardment could occur without capture of the bombarding particle, but Harkins showed evidence (measured energy losses) that in forming an excited nucleus capture always occurs; by 1936 Harkins’ view was accepted.

Harkins’ eighty papers on nuclear reactions and isotopes include several important contributions to theory and experiment and for some years were the only significant American contributions in this field. The great bulk of his studies, however, concern surface phenomena. On Harkins’ first day at Karlsruhe in 1909 Fritz Haber greeted him with the toast, “He shall work on surface tension.” Although Harkins had no interest in this subject, he soon became intrigued when he found that current measuring techniques were grossly inaccurate. Following the example of Richards—whose precision in atomic weights brought him a Nobel Prize in 1914—Harkins strove to make surface measurements a precise science. Together with F. E. Brown in 1916–1919 Harkins brought high precision to the drop weight method for the measurement of surface and interfacial tension, an easier laboratory procedure than the method of capillary height measurement perfected by Richards. Eleven years later Harkins and Hubert Fairlee Jordan achieved similar precision with the ring method. Harkins publications remain the primary references on the drop weight and ring methods of measurement.

Precise measurements of surface and interfacial tensions allowed new interpretations and understanding. Between 1910 and 1920, when electron shifts in organic compounds had gained the attention of physical chemists, Harkins explored the relation of structure of organic molecules to their surface properties. A short time after the publication of Langmuir’s landmark paper on gas adsorption, Harkins published two extensive papers (1917) on precisely measured surface tensions and interfacial tensions, versus water, for 338 different organic compounds, in which he cited evidence for oriented monomolecular films in surfaces and interfaces. Langmuir’s publication, a month later, on oriented monomolecular films of insoluble polar organic molecules on water, led to competition between the two scientists. In 1920 Harkins’ formalized his views on oriented monolayers at interfaces with the concepts of “work of adhesion,” “work of cohesion,” and the “spreading coefficient.” These concepts are widely used to correlate the spreading of organic materials on water or mercury.

Harkins’ series of publications on monomolecular films at liquid surfaces or interfaces stretched over a twenty-year period. Beginning in 1925 he made precise studies of the adsorption of soluble films and of film properties of insoluble films. He investigated two-component monolayers and types of organic molecules, including enzymes and polymers. In addition he applied his research on monolayers adsorbed at the oil-water interface and at the liquid-solid interface toward a better understanding of emulsions and pigment dispersions.

In about 1937 Harkins initiated a major effort in the study of gas adsorption on solid powders. These studies led to a series of papers, from 1942 to 1950, which remain basic to our present understanding of this subject. Together with George Edward Boyd, George Jura, and others, he made important and novel use of calorimetric measurements with finely divided powders. They developed the only absolute method for measuring surface areas of powders, based on the heats of immersion in a liquid of powders already equilibrated with saturated vapor of the same liquid. This method allowed calibration of relative methods such as the well-known Brunauer-Emmett-Teller (BET) method. Calorimetry was also used to measure the range of forces emanating from solid surfaces. Harkins’ investigations of the total free energy change per unit area of solid surfaces during gas adsorption up to equilibrium vapor pressures (designated “equilibrium spreading pressure”) form the basis of much of our knowledge of adsorption on oxides.

Although Harkins was sixty-eight when the United States entered World War II, rather than retire, he plunged into a new field of colloid chemistry, the emulsion polymerization of rubber. Together with M. L. Corrin and H. B. Klevens he developed new methods for measuring micelle formation in detergent solutions and then related the effect of structure, salts, hydrocarbons, and insoluble surfactants quantitatively to micelle formation. Harkins correlated these criteria with the conditions found to be optimum for emulsion polymerization and thus provided the fundamentals for understanding this important process.

Throughout his career, Harkins showed exceptional foresight in choosing important fields of research. His intuition in predicting phenomena, coupled with a strong drive to measure important properties with great accuracy, provided a legacy that includes basic precepts of nuclear reactions, a general outlook on surface chemistry, laboratory methods for surface studies, and a great many unequaled measurements of surface properties.

BIBLIOGRAPHY

Most of Harkins’ publications are listed in his The Physical Chemistry of Surface Films (New York, 1952), pp. 375–390, posthumously edited by Thomas Frazer Young.

Additional information is in J. R. Partington, A History of Chemistry, IV (London-New York, 1964), 934, 950, 952–953, 966; Poggendorff, VIIb, 1847–1851; Gustav Egloff, Chemical and Engineering News, 22 , no. 10 (1944), 804–805; an anonymous article, ibid., 27 (1949), 1146.

Frederick M. Fowkes