The American chemist Theodore William Richards (1868-1928) ushered in a new age of accuracy in chemistry by determining the atomic weights of many elements.

Theodore W. Richards was born on Jan. 31, 1868, in Germantown, Pa. His father, William Trost Richards, was a prominent landscape and marine artist; his mother, Anna Matlock Richards, was a poet and a woman of great cultivation. Until he entered college, his education was at home under his mother's direction. At age 14 he entered Haverford College as a sophomore, uncertain whether to become an astronomer or a chemist. He had defective eyesight, however, and by the time of his graduation he had decided on a career in chemistry.

In 1885 Richards entered Harvard as a senior and the following year was granted the bachelor's degree. Two years later he was awarded the doctorate with a dissertation on the atomic weights of hydrogen and oxygen. He won a Harvard grant for a year of travel and study in Europe. On his return to Harvard in 1889, he became an assistant and subsequently an instructor in analytical chemistry.

Atomic Weight Determinations

To Richards, atomic weights were the most fundamental constants in nature, and he associated them with deep questions about the universe. They offered more promise of contributing to the understanding of the universe than any other area of chemistry. By very thorough, painstaking work he published revised atomic weights for copper, zinc, barium, strontium, magnesium, and calcium.

In 1894 Richards introduced two new devices to overcome the two most prevalent sources of error in atomic weight work: the presence of moisture and the loss of traces of precipitate. His bottling apparatus enabled him to fuse, handle, and weigh solids under absolutely dry conditions. His nephelometer (cloud measurer) enabled him to determine traces of unrecovered precipitate by measuring the turbidity of the filtrate.

Along with his research Richards was teaching quantitative analysis. In 1894 he was promoted to assistant professor. Harvard sent him to Germany for a year of training in physical chemistry. On his return from Europe in 1896 he married Miriam Stuart Thayer.

Over the next few years Richards corrected the atomic weights of nickel, cobalt, iron, uranium, and cesium. In every instance his results became the official ones of the International Commission on Atomic Weights. His revision of the atomic weights of J. S. Stas involved correcting for errors in purification, drying, and weighing of materials, and it inaugurated a new era of accuracy. His papers published from 1905 to 1910 exceeded in accuracy any chemical research ever published.

In 1901 Richards was promoted to full professor, and in 1912 he became Erving professor of chemistry and director of the new Wolcott Gibbs Memorial Laboratory (1913), which was the finest chemical laboratory in the world.

By 1913 the study of radioactive decay led to the possibility that an element may have more than one atomic weight. Richards analyzed radioactive samples of lead, and all of his determinations were below the atomic weight of ordinary lead, the lowest being 206.08. He concluded that there was no doubt that uranium transmuted itself into a light variety of lead. Frederick Soddy announced the isotope concept in 1913, and Richards's experiments were the first confirmation of the new theory and the only conclusive evidence for isotopes until the development of the mass spectrograph.

Atomic weights have remained the most frequently required units by chemists in quantitative measurements of all kinds. Richards determined the atomic weights of 25 elements. His students, Gregory Baxter at Harvard and Otto Hönigschmidt at Munich, continued his work and were responsible for 30 additional elements.

Physical Chemistry

Of Richards's almost 300 papers, about one-half deal with atomic weights, the remainder being concerned with several aspects of physical chemistry. He was a leader in introducing this new field into the United States, and his laboratory was a center which prepared a new generation of physical chemists. Richards made investigations in thermochemistry, electrochemistry, and the physicochemical study of the properties of matter. In physical chemistry, as in atomic weights, his work represented an advance in precision and accuracy.

One of Richards's most productive areas of research was thermochemistry. In 1905 he introduced the adiabatic calorimeter to prevent the loss or gain of heat to and from the surroundings. He published over 60 papers on thermochemistry and for many years was a pioneer in precision calorimetry.

In 1899 Richards began a study of the atomic volumes and compressibilities of the elements after noting that the constant b occurring in the Van der Waals equation (p + a/V²) (V - b) = RT was not a constant but varied with pressure and temperature. Since b was the space occupied by the molecule, Richards asserted that the concept of the atom as a hard, rigid particle was incorrect. He proposed that atoms were compressible, the forces of affinity and cohesion exerting a compressing effect on atoms resulting in enormous internal pressures. He devised methods to determine the compressibilities of the elements up to 500 atmospheres pressure and tried to correlate this property with the other fundamental properties of the elements in the hope of discovering important relationships. He never completed these studies; nevertheless, his experimental data proved to be invaluable to atomic physics.

His Character and Honors

Richards was primarily an experimentalist of exceptional ability. Yet his measurements were only a means to an end; with them he searched for an understanding of the material structure of the universe.

Richards received many honorary degrees and medals. A Harvard professorship was endowed in his name in 1925. He received the Nobel Prize in chemistry in 1914, the first American chemist to be so honored. He was a man of noble character who made a deep impression on those who met him. The guiding principles of his life he described as "kindliness and common sense." He died on April 2, 1928.

Further Reading

• Richards presented his atomic weight research in Determinations of Atomic Weights (1910). In his Nobel Prize lecture, printed in Nobel Foundation, Nobel Lectures: Chemistry, 1901-1921 (1966), he described both his research and his beliefs about the universe. Of the many biographical studies of Richards, the most informative are those in Benjamin Harrow, Eminent Chemists of Our Time (1927); Sir Harold Hartley, Memorial Lectures Delivered before the Chemical Society (3 vols., 1933); and Aaron J. Ihde, Great Chemists (1961).