death. According to Forbes, by 1932 the atomic weights of 55 elements had been studied by Richards and his students. Among the potential sources of error Richards uncovered in such determinations was the tendency of certain salts to occlude gases or foreign solutes on precipitation. As an example of the care Richards used in his work, Emsley reports that he carried out 15,000 recrystallizations of thulium bromate in order to obtain the pure element thulium for an atomic weight measurement. Richards was the first to show, by chemical analysis, that an element could have different atomic weights. He was asked to analyze samples of naturally occurring lead and lead produced by radioactive decay. His measurements showed that the two samples had different atomic weights, supporting the concepts of isotopes. Although Richards's chemical determinations of atomic weights were highly significant for their time, they have largely been superseded. Modern scientists use electronic instrumentation, such as mass spectrometers, to determine both the masses and the abundances of an element's isotopes. From this information, an average atomic mass can be calculated, and compared to the values measured by Richards. The modern methods are faster and more sensitive than those on which Richards had to rely, but not necessarily less expensive. Other scientific work of Theodore Richards included investigations of the compressibilities of atoms, heats of solution and neutralization, and the electrochemistry of amalgams. His investigation of electrochemical potentials at low temperatures was among the work that led, in the hands of others, to the Nernst heat theorem and the Third law of thermodynamics, although not without heated debate between Nernst and Richards. Richards also is credited with the invention of the adiabatic calorimeter as well as the nephelometer, which was devised for his work on the atomic weight of strontium. Legacy and honors Member of the American Philosophical Society (1902) Lowell Lectures (1908) Davy Medal (1910) Faraday Lectureship (1911) Willard Gibbs Medal (1912) President of the American Chemical Society (1914) Nobel Prize in Chemistry (1914) Franklin Medal (1916) President of the American Association for the Advancement of Science (1917) Honorary Member of the Royal Irish Academy (1918) Foreign Member of the Royal Society of London (1919) President of the American Academy of Arts and Sciences President (1919 – 1921) Lavoisier Medal (1922) Le Blanc Medal (1922) Honorary Fellow of the Royal Society of Edinburgh (1923) Member of the International Atomic Weights Committee Theodore