Kraus, Charles August

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Kraus, Charles August

(b. Knightsville, Indiana, 15 August 1875; d. East Providence, Rhode Island, 27 June 1967)


Although he spent most of his childhood on a Kansas farm, Kraus developed a strong interest in physics and electrical engineering. He entered the University of Kansas in 1894. In his junior year he coauthored a paper on spectroscopy, and he received his bachelor’s degree in engineering in 1898. After a year’s further study at Kansas and a year as research fellow at Johns Hopkins University, he served as an instructor of physics at the University of California from 1901 until 1904. He then became a research assistant at the Massachusetts Institute of Technology, where he received his doctorate in chemistry in 1908.After graduation he remained at MIT as research associate (1908-1912) and assistant professor of physical chemical research (1912-1914).

In 1914 he was named professor of chemistry and head of the chemical laboratory at Clark University, where he remained for nine years. He became professor of chemistry and director of chemical research at Brown University in 1924. Although he retired from the position in 1946, he continued his research and was working on a book when he died in 1967 at the age of ninety-one. During World War I he was active in government service. Kraus received five honorary degrees, the Willard Gibbs Medal (1935), and the Priestley Medal (1950) of the American Chemical Society.

Kraus’s studies in chemical research began at the University of Kansas, where Hamilton P. Cady and Edward C. Franklin became interested in liquid ammonia solutions. Kraus was attracted by the opportunities that appeared in the field, especially by the study of solutions of the alkali metals. Using the glassblowing experience he had gained in Germany, Franklin, in conjunction with Kraus, published eight papers between 1898 and 1905, dealing with such problems as the solubility of substances in liquid ammonia, the molecular rise in the boiling point of a solution of a solute in liquid ammonia as the molal concentration of the solution is increased; and various physical properties of the solutions.

Continuing his research on liquid ammonia at MIT, Kraus published a series of articles (beginning in 1907).He reported that alkali and alkaline earth metals could form solutions with ammonia. Highly concen. trated solutions would behave like metals while dilute solutions would resemble ionic solutions of salts. The dilute solutions ionize to give the normal positive metal ion and negative electrons, the latter associated with large amounts of ammonia. Gilbert N. Lewis remarked on Kraus’s “extraordinary experimental skill” in designing and constructing glass apparatus, which was largely responsible for his successful studies.

At Clark University, Kraus studied other physical properties of metal ammonia solutions, notably density, conductivity, and vapor pressure. His results indicated beyond any doubt that alkali metals do not form compounds with ammonia, but alkaline earths do form compounds by combining with six molecules of ammonia to produce metal-like ammoniates.

His interest in radicals that exhibit metallic proper. ties led to studies of alkyl mercury and ammonium and substituted ammonium groups. From these groups he then turned to work on organic radicals bonded to group four metals. He published over twenty-five papers on these metal-organic systems; many of the studies were carried out in liquid ammonia solutions because of the water or air sensitivity of most of the compounds.

Around 1920 Thomas Midgley, Jr., and T. A. Boyd of General Motors discovered that tetraethyl lead would reduce engine knocking when added to gasoline. As a consultant to Standard Oil Company of New Jersey, Kraus was asked to design an economical quantity synthesis of this substance. After a three. month intensive study with Conrall C. Callis late in 1922, Kraus succeeded in producing a reaction between a lead-sodium alloy and ethyl chloride under high pressures and relatively low temperatures followed by steam distillation. This discovery permitted the automobile industry to develop high compression engines.

Further studies at Clark and Brown concerned the electrical properties of substances dissolved in solvents of very low dielectric constant such as benzene, dioxane, and ethylene dichloride. Of particular interest are his studies of large anions and cations, which have led to a clearer picture of the nature of electrolyte solutions.

During World War II he worked with the navy and served as a consultant to the Manhattan Project. Specifically he was instrumental in working out a process for purifying uranium salts.


I. Original Works. Among Kraus’s more significant publications are “Solutions of the Metals in Non-metallic Solvents. I. General Properties of Solutions of Metals in Liquid Ammonia,” in Journal of the American Chemical Society, 29 (1907), 1556-1571; “Solutions … II. On the Formation of Compounds between Metals and Ammonia,” ibid., 30 (1908), 653-668; and “General Relations Between the Concentration and the Conductance of Ionized Sub. stances in Various Solvents,” ibid., 35 (1913), 1315-1434, written with W. C. Bray. These papers give sufficient refer. ences to Kraus’s earlier work. His tetraethyl lead studies received U.S. Patent Numbers 1,612,131 (28 Dec. 1926);1,694,268 (4 Dec. 1928); and 1,697,245 (1 Jan. 1929).

II. Secondary Literature. R. M. Fuoss published a memoir of Kraus in the Biographical Memoirs of the National Academy of Sciences, 42 (1971), 119-159. A detailed, but incomplete, discussion of Kraus’s early achievements is Warren C. Johnson, “The Scientific Work of Charles A. Kraus,” in The Chemical Bulletin, 22 (1935), 123-127. A helpful obituary notice appeared in Chemical and Engineering News, 45 (July 17, 1967). p. 59. In this latter article, his birth year is incorrectly given as 1865.The G. N. Lewis quotation in the text comes from John. son’s article.

Sheldon J. Kopperl