Cavendish's leftover bubble of air turned out to be argon, a century later
In 1785 Henry Cavendish stripped oxygen and nitrogen from a sample of air and found a tiny bubble that refused to react. He had not made a mistake. More than a hundred years later William Ramsay and Lord Rayleigh realised the stubborn residue was argon, a gas nobody yet knew existed.
Cavendish was born in Nice on 10 October 1731 into one of Britain's grandest families, grandson of two dukes. His mother died before he turned two. He left Cambridge in 1751 without a degree, as many did then, and set up a laboratory in his father's London home. His father, Lord Charles, brought him into the Royal Society in the late 1750s, and Henry joined it and its dining club in 1760, attending faithfully for the rest of his life while shunning politics.
He is best known for hydrogen. Robert Boyle and others had made the gas earlier, but Cavendish is credited with recognising it as a distinct substance, which he called inflammable air, describing its density in his 1766 paper Factitious Airs. Lavoisier later repeated the work and named the element. Cavendish showed that burning hydrogen produced water, reporting this to Joseph Priestley by March 1783 but publishing a year later, which sparked a priority dispute with James Watt. He also found that exhaled air becomes fixed air, carbon dioxide, contrary to Priestley's prediction.
His hallmark was precision. He repeated experiments, averaged results and allowed for sources of error, using one of the century's first precision balances, made by a craftsman named Harrison. From his air analyses he concluded that ordinary air holds one part oxygen to four parts nitrogen. He also measured Earth's density, and hence its mass, in what is now called the Cavendish experiment, which also informs the gravitational constant. In the 1760s he explained heat as the motion of matter, and in 1787 he became one of the first outside France to accept Lavoisier's new chemistry.
He was intensely private. He published no books and only a few papers, leaving work on mechanics, optics and magnetism largely in manuscripts. His associate Charles Blagden helped keep the world at bay. Cavendish died on 24 February 1810.
Source: Henry Cavendish
