In July 1898, Marie and Pierre Curie announced the discovery of a new chemical element. They had isolated it from pitchblende, a uranium-bearing mineral, through a painstaking series of chemical separations guided by radioactivity measurements. The element was approximately 400 times more radioactive than uranium. They could have named it anything.
Marie Curie named it polonium, after Poland.
This was not a neutral choice. In 1898, Poland did not exist as an independent state. It had been partitioned in 1795 among Russia, Prussia, and Austria, and its territory had been divided among three empires for over a century. Polish language, culture, and identity were actively suppressed by the occupying powers, particularly by Russia, which controlled the largest portion including Warsaw, where Marie Curie (born Maria Skłodowska) had grown up.
Naming an element after a country that had been erased from the map of Europe was a deliberate act of defiance. It placed the word “Poland” in the permanent vocabulary of science, in every periodic table, in every chemistry textbook, in every language on Earth. No political decree could undo it. As long as the periodic table exists, polonium will remind the world that Poland existed, even when its borders did not.
How Polonium Was Found
The discovery of polonium was not an accident. It was the result of a systematic investigation that began with a simple but powerful observation.
Marie Curie had been studying the radioactivity of uranium compounds as part of her doctoral research, begun in late 1897. Using a piezoelectric electrometer (an instrument designed by Pierre Curie and his brother Jacques), she measured the ionizing radiation emitted by every uranium compound she could obtain. The results confirmed what Henri Becquerel had discovered in 1896: uranium emits penetrating rays spontaneously.
But Curie went further than Becquerel. She tested not just uranium compounds but every element and mineral available to her. She discovered that thorium is also radioactive (a finding made independently by Gerhard Carl Schmidt in Germany). And she made the crucial observation that the radioactivity of a compound depends only on the amount of the radioactive element it contains, not on its chemical form. This led her to conclude that radioactivity is an atomic property, a characteristic of the atom itself rather than a product of chemistry.
Then came the anomaly that changed everything. When Curie measured the radioactivity of pitchblende, a complex mineral containing uranium, she found that it was more radioactive than pure uranium. The same was true of chalcolite, another uranium mineral. This was impossible if uranium was the only radioactive element in these minerals. The excess radioactivity had to come from something else: an unknown element, present in tiny quantities, that was more radioactive than uranium.
The Chemical Hunt
Pierre Curie joined Marie’s research at this point, and together they began the chemical analysis of pitchblende, fraction by fraction. Their method was innovative: instead of relying on chemical tests alone, they used radioactivity as a guide. At each step of the chemical separation, they measured which fraction carried the most radioactivity. The fraction with the highest radioactivity contained the unknown element.
Pitchblende is a complex mineral containing dozens of elements. The Curies dissolved it in acid and separated it into chemical groups using standard analytical techniques: precipitation, filtration, dissolution, re-precipitation. At each step, they tracked the radioactivity. It was detective work, with the electrometer as their compass.
The radioactivity concentrated in two different chemical fractions. One fraction behaved like bismuth: it precipitated with hydrogen sulfide in acidic solution and had chemical properties similar to bismuth. The other fraction behaved like barium: it precipitated as an insoluble chloride and co-crystallized with barium chloride.
The bismuth-like fraction was investigated first. By repeated precipitation and measurement, the Curies showed that this fraction contained a substance far more radioactive than bismuth itself. In their paper of July 1898, they wrote: “We believe that the substance we have extracted from pitchblende contains a metal not yet described, akin to bismuth in its analytical properties. If the existence of this new metal is confirmed, we propose to call it polonium, after the name of the country of origin of one of us.”
The understatement was characteristic of Marie Curie’s scientific writing. But the political message was unmistakable.
The Difficult Element
Polonium proved to be one of the most challenging elements ever studied. It was present in pitchblende at extraordinarily low concentrations (approximately one part per thirty million), far lower even than radium. Isolating a visible quantity required processing enormous amounts of raw material.
More problematically, polonium is intensely radioactive and has a relatively short half-life (138 days for its most stable isotope, polonium-209, but only 138 days for the isotope the Curies were working with, polonium-210). This means that any sample of polonium steadily disappears, decaying into lead. A sample that is strongly radioactive one month is noticeably weaker the next. Within a year, most of it is gone.
This made polonium much harder to study than radium, which has a half-life of 1,600 years and could be accumulated and preserved. The Curies quickly realized that radium was the more practical element to isolate and characterize, and their subsequent work focused primarily on radium. Marie Curie eventually isolated one-tenth of a gram of pure radium chloride, enough to measure its atomic weight and record its emission spectrum. Polonium, by contrast, was never isolated in comparable quantities during Curie’s lifetime.
It was not until 1910 that Marie Curie, working with André-Louis Debierne, succeeded in isolating a few milligrams of metallic polonium. Even then, the element’s rapid decay made it almost impossible to study in bulk.
The Science of Polonium
Despite its elusiveness, polonium proved scientifically significant in several ways:
- Alpha radiation. Polonium is an intense emitter of alpha particles (helium nuclei). In fact, it emits almost exclusively alpha radiation, with very little beta or gamma radiation. This made it useful as a pure alpha source in later experiments, including those by Rutherford and others who used alpha particles to probe the structure of the atom.
- Decay chains. Polonium-210 is the final radioactive element in the uranium-238 decay chain, decaying into stable lead-206. Its discovery helped researchers map the sequence of radioactive transformations by which uranium slowly converts to lead over billions of years.
- Atomic structure. The existence of polonium, with atomic number 84, helped fill gaps in the periodic table and confirmed Mendeleev’s prediction that undiscovered elements existed between bismuth (83) and radon (86).
Polonium also turned out to be far more dangerous than the Curies could have known. Because it emits alpha particles, which are easily stopped by skin but devastating to internal organs, polonium is one of the most toxic substances known when ingested or inhaled. A microgram (one-millionth of a gram) is a lethal dose. The Curies, who handled radioactive materials daily without protection, were exposed to polonium along with radium and other radioactive substances throughout their careers.
Poland and the Periodic Table
Marie Curie’s decision to name her first discovered element after Poland was part of a broader pattern of scientific nationalism in the naming of elements. Gallium (France), germanium (Germany), scandium (Scandinavia), ruthenium (Russia), and hafnium (Copenhagen, from the Latin Hafnia) all carry national identities in their names. But polonium was unique: it was named not for an existing country but for a vanished one, a nation that existed only in the hearts of its exiled and oppressed people.
The naming had real political resonance. The announcement of polonium’s discovery in 1898 was covered by newspapers across Europe, and the name drew attention to the Polish question at a time when the partition of Poland was rarely discussed in Western European politics. Marie Curie, who had left Warsaw for Paris in 1891 partly to escape Russian restrictions on women’s education, never forgot her origins. Her scientific work in Paris was, among other things, a demonstration that Polish talent and intellect could flourish when given the opportunity that occupied Poland denied.
Poland regained its independence in 1918, twenty years after the discovery of polonium. Marie Curie lived to see it happen. She visited Warsaw multiple times in the 1920s and 1930s, and she helped establish the Radium Institute in Warsaw (now the Maria Skłodowska-Curie National Research Institute of Oncology). The element she had named for a dream became the element of a real country.
Reading the Evidence
The discovery of polonium is described in Marie Curie’s doctoral thesis, defended at the Sorbonne in 1903. The thesis, titled Recherches sur les substances radioactives, presents the full sequence of experiments: the systematic survey of radioactive elements, the anomalous radioactivity of pitchblende, the chemical hunt for the unknown elements, and the announcement of both polonium and radium. It is a masterclass in experimental reasoning, written with the clarity and precision that characterize all of Curie’s scientific work.
The Kronecker Wallis bilingual edition presents the French original from one cover and the English translation from the other. Reading the thesis, one can follow Curie’s reasoning step by step, from the first measurements of uranium salts to the identification of two new elements. The discovery of polonium, the element that carries a nation’s name through every periodic table on Earth, begins on those pages.
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