My experience in growing crystals for condensed matter physics has been sealing grams of material in ampoules which get heated in laboratory furnaces, so I don't have the experience to understand how Marie Curie managed to go through tons of pitchblende to isolate radium, especially given her limited resources. How were the samples heated, and how would she have kept her samples from getting oxidized? It seems like making lots and lots of ampoules would be impractical.

  • $\begingroup$ Why is making lots of ampoules impractical? That is what chemists did. $\endgroup$ – Jon Custer Sep 17 at 23:44

Marie Curie's work was detailed in the French Journal L'Actualité chimique, $352$, p. V, May $2011$. It is called "Dossier Marie Curie" and was published just $100$ years after Marie Curie's Nobel Prize Conference in $1911$. She used beakers, Bunsen burners, filter paper and funnel. That is all.

It could be summarized this way. Marie Curie extracted first all the heavy elements from $30$ kg of the mineral pechblende, using successive and selective precipitation techniques. At the end she obtained $40$ g pure $\ce{BaCl2}$, with Radium as only impurity ($10$ mg $\ce{RaCl2}$ ; $0.025$ ppm).

Now starts the real purification process. She dissolved this $40$ g $\ce{BaCl2}$ in the minimum amount of boiling water ($68$ g), let it cool down. She obtained a cristalline deposit $\ce{D1}$ containing $16$ g $\ce{BaCl2}$ and $8,3$ mg $\ce{RaCl2}$ ($0.05$ ppm) : the proportion of Radium has increased in the recrystallized solid. She redissolved these $16$ g $\ce{BaCl2}$ in the minimum amount of hot water ($27$ g), let it cool down, to obtain a recrystallized deposit $\ce{D2}$ containing $6.4$ g $\ce{BaCl2}$ and $6.9$ mg $\ce{RaCl2}$. Once again the new deposit $\ce{D2}$ contains more radium ($1$ ppm). Repeating this procedure twice leads to deposits $\ce{D3}$ ($2.6$ g $\ce{BaCl2}$ and $5.8$ mg $\ce{RaCl2}$, $2$ ppm)} and $\ce{D4}$ ($1.0$ g $\ce{BaCl2}$ and $4.8$ mg Ra, $4$ ppm) ($4.0$ ppm). The proportion of radium increased steadily, but the mass of enriched $\ce{BaCl2}$ decreased.

Waste waters from $\ce{D1}$,$\ce{D2}$,$\ce{D3}$,$\ce{D4}$ are all saved. mixed and evaporated so as to save the rest of $\ce{BaCl2}$ ($39$ g) and the rest of radium ($5.2$ mg}. The whole series of recrystallization is repeated, and repeated over and over again. See the detailed report in l'Actualité chimique, if you are interested.

After repeating this tedious series of similar recrystallizations may be more than one thousand times, and starting again and repeating it with $40$ times the original amounts of pechblende (30 kg), she was able to get a final sample made of $0.17$ g $\ce{RaCl2}$ containing only $0.01$ g $\ce{BaCl2}$. This is $\ce{RaCl2}$ at $94$% purity. Enough to get the Nobel Prize in Chemistry.

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After searching Google Books, I found autobiographical notes from Marie Curie. Apparently, it was radium chloride that was isolated first, not elemental radium. Salts can often be precipitated from solution at much lower temperatures than those needed to melt many inorganic materials, and you typically wouldn't need to shield a solution from air, so ampoules wouldn't be needed. This would be the case for fractional crystallization, which she mentions in her autobiographical notes. (She also mentions spending whole days "mixing a boiling mass with a heavy iron rod". I'm not sure if she's referring to mixing molten material or a solution in water or acid.) She also says they eventually used a factory; as time passed and their work became "more and more known", she was able to do the "crude processes" in a factory, allowing herself "more time to the delicate finishing treatment".

source: the book Pierre Curie: with Autobiographical Notes by Marie Curie

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  • 5
    $\begingroup$ Great information, but could you provide a link to the source? $\endgroup$ – Karsten Theis Sep 18 at 1:45
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    $\begingroup$ Most of the work of elemental separation was done by dissolving the minerals in various acids and them using chemistry to separate the salts. She certainly didn't melt the minerals. $\endgroup$ – matt_black Sep 18 at 15:50

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