This is the paper where Marie Curie announced the discovery of Radium.
It came out only 6 months after the Polonium paper and ended up in the same tome of the Comptes rendus de l'Académie des Sciences, number 127 which is funny.
French text on Wikisource: fr.wikisource.org/wiki/Œuvres_de_Pierre_Curie/24. It's from a 1908 collection of works, and it has made minor corretions, such as using "radioactive" without dash instead of "radio-active" to update the terminology a bit, which is a crime!
The original can be found inside the original tome PDF: archive.org/details/ComptesRendusAcademieDesSciences0127/page/n5/mode/2up
An English translation by the American Institute of Physics: history.aip.org/exhibits/curie/discover.htm
Basically they extracted a Barium solution, but were unable to separate Barium and Radium. If you look at a periodic table, you will see that Radium is directly below radium which explains it as they have very similar chemical properties.
Two of us have shown that by purely chemical procedures it is possible to extract from pitchblende a strongly radio-active substance. This substance is related to bismuth by its analytical properties. We have expressed the opinion that perhaps the pitchblende contained a new element, for which we have proposed the name of polonium.The investigations which we are following at present are in agreement with the first results we obtained, but in the course of these investigations we have come upon a second, strongly radio-active substance, entirely different from the first in its chemical properties. Specifically, polonium is precipitated from acid solution by hydrogen sulfide; its salts are soluble in acids and water precipitates them from solution; polonium is completely precipitated by ammonia.The new radio-active substance which we have just found has all the chemical appearance of nearly pure barium: it is not precipitated either by hydrogen sulfide or by ammonium sulfide, nor by ammonia; its sulfate is insoluble in water and in acids; its carbonate is insoluble in water; its chloride, very soluble in water, is insoluble in concentrated hydrochloric acid and in alcohol. Finally this substance gives the easily recognized spectrum of barium.We believe nevertheless that this substance, although constituted in its major part by barium, contains in addition a new element which gives it its radio-activity, and which, in addition, is closely related to barium in its chemical properties.
Like with Polonium they once again found a new spectral line, though it was somewhat weak in this case as they didn't manage to purify as much:
M. Demarçay has consented to examine the spectrum of our substance with a kindness which we cannot acknowledge too much. The results of his examinations are given in a special Note at the end of ours. Demarçay has found one line in the spectrum which does not seem due to any known element. This line, hardly visible with the chloride 60 times more active than uranium, has become prominent with the chloride enriched by fractionation to an activity 900 times that of uranium. The intensity of this line increases, then, at the same time as the radio-activity; that, we think, is a very serious reason for attributing it to the radio-active part of our substance.
Name the thing:
The various reasons which we have enumerated lead us to believe that the new radio-active substance contains a new element to which we propose to give the name of radium.
They did not have enough purity to clearly measure the mass difference:
but it is cute to see that they called radium as "active barium".
We have measured the atomic weight of our active barium, determining the chlorine in its anhydrous chloride. We have found numbers which differ very little from those obtained in parallel measurements on inactive barium chloride; the numbers for the active barium are always a little larger, but the difference is of the order of magnitude of the experimental errors.
Polonium and radium can be used as a light source without power source, so oops, it looks like we broke the conservation of energy!
Later on radium came to be used as a phosphorescent light source for things like watch handles, which led to girls getting cancer in the factories; the Radium Girls.
The new radio-active substance certainly includes a very large portion of barium; in spite of that, the radio-activity is considerable. The radio-activity of radium then must be enormous.Uranium, thorium, polonium, radium, and their compounds make the air a conductor of electricity and act photographically on sensitive plates. In these respects, polonium and radium are considerably more active than uranium and thorium. On photographic plates one obtains good impressions with radium and polonium in a half-minute's exposure; several hours are needed to obtain the same result with uranium and thorium.The rays emitted by the components of polonium and radium make barium platinocyanide fluorescent; their action in this regard is analogous to that of the Röntgen rays, but considerably weaker. To perform the experiment, one lays over the active substance a very thin aluminum foil on which is spread a thin layer of barium platinocyanide; in the darkness the platinocyanide appears faintly luminous above the active substance.In this manner a source of light is obtained, which is very feeble to tell the truth, but which operates without a source of energy. Here is at least an apparent contradiction to Carnot's Principle.Uranium and thorium give no light under these conditions, their action being probably too weak.
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