SCATCHARD, GEORGE

(b. Oneonta, New York, 19 March 1892; d. Cambridge, Massachusetts, 10 December 1973). physical chemistry.

Scatchard was an authority on the physical chemistry of solutions. He investigated the equilibria thermodynamics, and kinetics of aqueous and nonaqueous solutions, electrolytes and nonelectrolytes, and solutions of small and large molecules, especially proteins. Scatchard stressed the similarities that existed among solutions rather than their differences, and tried to keep his descriptions of them general and free from assumptions and restrictions. In his lifetime he published 165 papers.

Scatchard was the second son and fourth child of Elmer Ellsworth Scatchard and Fanny Lavinia Harmer. After his early education at Oneonta Normal School (1898-1909), Scatchard entered Amherst College, graduating in 1913 with a degree in chemistry. He received the Ph.D. from Columbia in 1917, having studied under the organic chemist Marston T. Bogert. After graduation Scatchard remained at Columbia, assisting Alexander Smith, But once the United States entered World War I in April 1917, he also assisted W. K. Lewis of M.I.T., who was then at Columbia doing war research. In 1918 Scatchard was drafted and commissioned a first lieutenant in the army’s Sanitary Corps. He spent the war in France, at the Sorbonne, where he worked with Victor Grignard on the development of a rapid and sensitive method for detecting small airborne quantities of mustard gas.

In 1919 Scatchard received one of the newly established National Research Council fellowships but declined it in favor of a teaching position at Amherst. He stayed there for four years, investigating the hydration of sucrose from vapor pressure measurements and the reaction rate and mechanism of the sucrose inversion in concentrated solutions. This work showed the advantage of using mole fractions instead of volume concentrations. It was done prior to the introduction in 1922 of Johannes Brönsted’s theories of “specific ion interactions” and “critical complex reaction rates” (today called the activated complex) and the Debye-Hückel theory of interionic attraction in 1923. Scatchard went to the Massachusetts Institute of Technology in 1923; on 28 July he married Willian Watson Beaumont. He remained there, except for the World War II years, until his death.

During the war years Scatchard spent part of each week in Boston, serving as acting director of the physical chemistry laboratory at M.I.T. and also working with Edwin Cohn of the Harvard Medical School on the fractionation of plasma proteins, and the remainder in New York, assisting Harold Urey at Columbia with the gaseous diffusion of uranium hexafluoride isotopes. In July 1946, he went to Berlin for six months to serve as scientific adviser to General Lucius D. Clay, deputy military governor in Berlin, and as the member of commissions charged with preventing the revival of German war research and liquidating its war potential.

At M.I.T., Scatchard expanded his research on solutions to include electrolytes, protein and other colloidal solutions, and the thermodynamics of non-electrolytic solutions, particularly their entropy and enthalpy of mixing. His studies on electrolytic solutions contributed significantly to the acceptance of the Debye-Hückel theory after its publication in 1923. According to their theory, the attractions among ions in a solution always produced an atmosphere of oppositely charged ions around each ion, and this atmosphere retarded the central ion’s motion upon application of an electric field to the solution. In ten papers appearing between 1932 and 1936, Scatchard and co-workers carried out an extensive freezing-point study of aqueous salt solutions that strongly supported Debye and Hückel.

Of fundamental importance was Scatchard’s extension of the Debye-Hückel theory to dipolar ions, large ions such as the amino acids, carrying two or more separate charges. This work became the basis for later investigations that established the dependence of a dipolar ion’s activity coefficient on the solution’s dielectric constant and ionic strength. His research on electrolytic solutions continued into the late 1940’s and showed that the Debye-Hückel model of ion atmospheres accounted equally well for the interionic attractions of strong electrolytes.

Scatchard once said he was only a “part-time colloid chemist”. But in this field he made major contributions, especially in applying thermodynamics to protein solutions. Scatchard’s interest began around 1924 and grew out of his many discussions with his long-time colleague and friend Edwin Cohn on the relation of the Debye-Hückel theory to the solubility of proteins in salt solutions. But not until Scatchard had worked with Cohn on the wartime blood plasma fractionation program to produce albumin and other proteins did independent investigations begin in his own laboratory. In these studies he measured the osmotic pressure of albumin solutions at different pH values and salt and protein concentrations. This was of great importance because the albumin was responsible for maintaining osmotic equilibrium between the plasma and the cells and tissues in contact with it.

Scatchard’s studies on osmotic pressures also led to protein molecular-weight determinations. Søren P. L. Sørenson in Copenhagen and G. S. Adair in Cambridge had already used osmotic pressures to calculate molecular weights of proteins, and by 1946 Scatchard extended the calculations to a broad range of protein concentrations and pH values. Further work on albumin solutions showed that albumin had a tendency to bind ions electively. To account for the binding on it and other macromolecules. Scatchard derived a simple relation for plotting the binding data, and from the plot he determined the number of binding sites on the molecule. This equation, first published in 1949, remains useful today.

Scatchard’s research on the thermodynamics of nonelectrolytic solutions began in 1931 when he published an equation that successfully predicted the magnitude of the enthalpy change upon mixing different solutions. While most chemists at that time agreed that the entropy change was ideal and that the deviation of real solutions from ideal behavior resulted from an enthalpy change, they disagreed in their interpretations. Scatchard believed the enthalpy was a quadratic function of the composition and argued for the use of volume fractions rather than mole fractions. Of the several interpretations proposed, his was the simplest and most successful for predicting the enthalpy on mixing because he established it completely from a solution’s physically determined properties (vapor pressure, density). In 1935 Scatchard introduced the term “excess free energy”, which he defined as the difference between free energies for real and ideal solutions. Excess functions still find general application in defining a solutions thermodynamic properties.

During his career Scatchard received many awards and honors. He was a National Research Council Fellow in 1923, and in 1931-1932 a Guggenheim Fellowship enabled him to study with such European scientists as Peter Debye in Leipzig. Scatchard was active in the American Chemical Society (ACS), and held membership in the National Academy of Sciences (1946), the New York Academy of Sciences, and the American Academy of Arts and Sciences. He was a Sigma Xi national lecturer in 1951. The ACS awarded him its Theodore W. Richards Medal in 1954, and in 1962 he received the Kendall Award in Colloid Science. The unpublished manuscripts of Scatchard’s texts on chemical thermodynamics and colloids have been published as Equilibrium in Solutions and Surface and Colloid Chemistry (1976).

BIBLIOGRAPHY

I. Original Works. Scatchard’s papers are in the archives of the Massachusetts Institute of Technology (two boxes, three linear feet). They contain reprints, reports, photographs, manuscripts, slides, and other material. John H. Edsall and Walter H. Stockmayer, “George Scatchard”, in Biographical Memoirs. National Academy of Sciences, 52 (1980), 335-377, contains a complete list of Scatchard’s publications, Scatchard’s Equilibrium in Solutions: Surface and Colloid Chemistry (Cambridge. Mass., 1976) has an introductory “Autobiographical Note” with a valuable commentary on each of his 165 publications. A second autobiographical account is Scatchard’s “Half a Century as a Part-Time Colloid Chemist”, in K. J. Mysele. C. M. Samour, and J. M. Hollister, eds., Twenty Years of Colloid and Surface Chemistry: The Kendall Award Addresses (Washington, D.C., 1973).

Scatchard’s important publications include “The Interaction of Electrolytes with Non-electrolytes”, in Chemical Reviews, 3 (1927), 383-402; “Equilibria in Non-electrolyte Solutions in Relation to the Vapor Pressures and Densities of the Components”, ibid., 8 (1931), 321-333; “Das Verhalten von Zwitterionen und von mehrwertigen lonen mit weit entfernten Ladungen in Elektrolytlösungen”, in Physikalische Zeitschrift, 33 (1932), 297-300, written with John G. Kirkwood; “The Coming of Age of the Interionic Attraction Theory”, in Chemical Reviews, 13 (1933), 7-27; “Concentrated Solutions of Strong Electrolytes”, ibid., 19 (1936), 309-327; chapters 3, 8 (with John T. Edsall), and 24 in Edwin J. Cohn and John T. Edsall, eds., Proteins, Amino Acids and Peptides (New York, 1943, repr. 1965); “Chemical, Clinical, and Immunological Studies on the Products of Human Plasma Fractionation. VI. The Osmotic Pressure of Plasma and of Serum Albumin”, in Journal of Clinical Investigation, 23 , (1944), 458-464, written with Alan C. Batchelder and Alexander Brown; “Chemical, Clinical, and Immunological Studies on the Products of Human Plasma Fractionation. XXVI. The Properties of Solutions of Human Serum Albumin of Low Salt Content”. ibid., 24 (1945), 671-679, written with L. E. Strong. W. L. Hughes, Jr., J. N. Ashworth, and A. H. Sparrow; “Physical Chemistry of Protein Solutions. I. Derivation of the Equations for the Osmotic Pressure”, in Journal of the American Chemical Society, 68 (1946), 2315-2319; “Preparation and Properties of Serum and Plasma Proteins. VI. Osmotic Equilibria in Concentrated Solutions of Serum Albumin and Sodium Chloride”, ibid., 2320-2329, written with Alan C. Batchelder and Alexander Brown; “Preparation and Properties of Serum and Plasma Proteins. VII. Osmotic Equilibria in Concentrated Solutions of Serum Albumin”, ibid., 2610-2612, written with Alan C. Batchelder, Alexander Brown, and Mary Zosa; “Physical-Chemical Characteristics of Certain of the Proteins of Normal Human Plasma”, in Journal of Physical and Colloid Chemistry, 51 (1947), 184-198, written with J. C. Oncley and Alexander Brown; “The Attractions of Proteins for Small Molecules and Ions”, in Annals of the New York Academy of Sciences, 51 (1949), 660-672; “Physical Chemistry of Protein Solutions. IV. The Combination of Human Serum Albumin with Chloride Ion”, in Journal of the American Chemical Society, 72 (1950), 535-540, written with I. Herbert Scheinberg and S. Howard Armstrong, Jr.; “Physical Chemistry of Protein Solutions”, V, The Combination of Human Serum Albumin with Thiocyanate Ion,” ibid., 540-546, written with I. Herbert Scheinberg and S. Howard Armstrong. Jr.; “Equilibria and Reaction Rates in Dilute Electrolyte Solutions,” in National Bureau of Standards (U.S.) Circular, no. 524 (1953), 185-192; “Physical Chemistry of Protein Solutions, X, The Binding of Small Anions by Serum Albumin,” in Journal of the American Chemical Society, 81 (1959), 6104-6109, written with Ying Victor Wu and Amy Lin Shen; and “Solutions of Electrolytes,” in Annual Review of Physical Chemistry, 14 (1963), 161-176.

II. Secondary Literature. The most complete account of Scatchard is Edsall and Stockmayer’s memoir. I. Herbert Scheinberg has written a shorter biographical account as an introduction to Scatchard’s Equilibrium in Solutions. Other articles on Scatchard are “Behavior of Serum Albumin;” in Chemical and Engineering News, 32 (24 May 1954), 2098-2099, on his receiving the ACS’s Theodore Richards Medal; and 40 (2 April 1962), 100, on his receiving the Kendall Company Award in Colloid Chemistry.

Anthony N. Stranges