Incoming links: Electromagnetic radiation
Not only did this open the way for X-ray crystallography, it more fundamentally clarified the nature of X-rays as being electromagnetic radiation, and helped further establish the atomic theory.
This is the papaer where Marie Curie announced the discovery of Polonium.
Here's a link with OCR on the French Wikisource: fr.wikisource.org/wiki/%C5%92uvres_de_Pierre_Curie/23. It's from a 1908 collection of works, but it is the exact same paper.
Here's an English translation: web.lemoyne.edu/~giunta/curiespo.html
First a recap of previous work:Note the cute terminology "Becquerel rays", which were only later understood to be electromagnetic radiation now known as gamma rays.
Some minerals containing uranium and thorium (pitchblende, chalcolite, uranite) are very active from the point of view of the emission of Becquerel rays. In a previous work, one of us showed that their activity is even greater than that of uranium and thorium, and expressed the opinion that this effect was due to some other very active substance contained in small quantities in these minerals.
Then some more recapitulation of the previously discussed groundbreaking idea that only atom counts matter for radioactivity, regardless of their chemical configuration as in fluorescence:
The study of compounds of uranium and thorium had shown, in fact, that the property of emitting rays which make air conductive and which act on photographic plates is a specific property of uranium and thorium which is found in all compounds of these metals, all the more weakened as the proportion of active metal in the compound is itself lower. The physical state of the substances seems to have a completely secondary importance. Various experiments have shown that the state of mixture of the substances seems to act only by varying the proportion of active bodies and the absorption produced by the inert substances. Certain causes (such as the presence of impurities) which act so powerfully on phosphorescence or fluorescence are therefore here completely without action. It therefore becomes very probable that if certain minerals are more active than uranium and thorium, it is because they contain a substance more active than these metals.
Then the key innovation: they used radioactivity measures to guide their purification work:
We have sought to isolate this substance in pitchblende, and experience has confirmed the above predictions.Our chemical research has been constantly guided by the control of the radiant activity of the products separated at each operation. Each product is placed on one of the plates of a condenser, and the conductivity acquired by the air is measured using an electrometer and a piezoelectric quartz, as in the work cited above. We thus have not only an indication but a number which accounts for the richness of the product in active substance.
Next they describe in high level their separation process, and I can't understand anything. But that's OK
Finally towards the end, bombs are dropped:
- the new elemnt is next to bismuth. If you stop now and look at a periodic table, you will see that bismuth is exactly one element before polonium
- "simple bodies" is their cute terminology for atoms, whose existence at the time not yet full aknowledged Section "History of the atomic theory"
- we call it polonium
By carrying out these various operations, we obtain increasingly active products. Finally, we obtained a substance whose activity is about 400 times greater than that of uranium.We have sought, among the bodies currently known, to see if there are any active ones. We have examined compounds of almost all simple bodies; thanks to the great kindness of several chemists, we have had samples of the rarest substances. Uranium and thorium are the only ones clearly active, tantalum is perhaps very weakly so.We therefore believe that the substance that we have removed from the pitchblende contains a metal not yet reported, close to bismuth by its analytical properties. If the existence of this new metal is confirmed, we propose to call it polonium, from the name of the country of origin of one of us.
They managed to purify it enough to look at the emission spectrum and it seems novel:
Mr. Demarçay was kind enough to examine the spectrum of the body that we are studying. He was unable to distinguish any characteristic line apart from those due to impurities. This fact does not support the idea of the existence of a new metal. However, Mr. Demarçay pointed out to us that uranium, thorium and tantalum offer particular spectra, formed of innumerable lines, very fine, difficult to perceive.
And once again, our radiation-based analytical chemistry technique is new:
Allow us to note that if the existence of a new element is confirmed, this discovery will be uniquely attributable to the new method of detection that Becquerel rays provide.
The history of light if funny.
First people thought it was a particle, as per corpuscular theory of light, notably Newton supported the corpuscular theory of light.
But then evidence of the diffraction of light start to become unbearably strong, culminating in the Arago spot.
And finally it was undertood from Maxwell's equations that light is a form of electromagnetic radiation, as its speed was perfectly predicted by the theory.
But then evidence of particle nature started to surface once again with the photoelectric effect. Physicists must have been driven mad by all these changes.