Metallic radium and the Traité de radioactivité

In August 1906, months after Pierre's death, Lord Kelvin argued in The Times that radium was not an element but a compound of lead and helium. Marie Curie answered with chemistry. She purified larger amounts of radium chloride and redetermined the atomic weight in 1907, close to the modern value of 226.

In 1910, with her colleague André Debierne, she went further. They passed an electric current through a radium chloride solution into a pool of mercury, then distilled the mercury away under hydrogen, leaving a white metal that blackened in air. "So I saw at last the mysterious white metal," she wrote, "but could not keep it in this state, for it was required for further experiments."

The same year she published the *Traité de radioactivité*, two dense volumes signed "Mme P. Curie". It laid out the theory, methods and data of a field that had not existed fifteen years earlier.