A Source Book in Physics

Author: Pierre Curie



Two of us have shown that by purely chemical processes we may extract from pitch blende a strongly radioactive substance. This substance stands near bismuth in its chemical properties. We have expressed the opinion that pitch blende perhaps contains a new element, for which we proposed the name polonium.

The researches which we have since carried on are in agreement with the first results obtained; but in the course of these researches we encountered a second substance also strongly radioactive and entirely different from the first in its chemical properties. In fact, polonium is precipitated in acid solution by sulphuretted hydrogen; its salts are soluble in acids, and water precipitates them from these solutions; polonium is completely precipitated by ammonia.

The new radioactive substance that we have found presents the chemical aspects of almost pure barium; it is not precipitated either by sulphuretted hydrogen or by ammonium sulphide, or by ammonia; the sulphate is insoluble in water and in acids; the carbonate is insoluble in water; the chloride, very soluble in water, is insoluble in concentrated hydrochloric acid and in alcohol. Finally, it gives the spectrum of barium, which is easy to recognize.

We believe, nevertheless, that this substance, although for the most part consisting of barium, contains in addition a new element which gives it its radioactivity and which furthermore is very near barium in its chemical properties. These are the reasons which speak in favor of this view.

(1) Barium and its compounds are not ordinarily radioactive; now, one of us has shown that radioactivity seems to be an atomic property, persisting in all the chemical and physical states of matter. If we look at the thing this way, the radioactivity of our substance, which does not arise from barium, ought to be attributed to another element.

(2) The first substances which we obtained, in the state of hydrated chlorides, had a radioactivity 60 times greater than that of metallic uranium. (The radioactivity intensity is evaluated by the conductibility of the air in our apparatus.) By dissolving these chlorides in water and precipitating a part of them by alcohol, the precipitated part is much more active than the part which remains dissolved. By starting with this fact we may carry out a series of fractionations, from which we may obtain more and more active chlorides. We have thus obtained chlorides which have an activity 900 times greater than that of uranium. We have been stopped by the lack of material, but from the progress of the operations we may assume that the activity would have been much more increased if we had been able to continue. These facts can be explained by the presence of a radioactive element of which the chloride is less soluble in alcoholic solution than is barium chloride.

(3) M. Demarçay has examined the spectrum of our substance, with a kindness for which we do not know how to thank him enough. The results of his observations are presented in a special note which follows ours. M. Demarçay has found in the spectrum a ray which seems not to belong to any known element. This ray, which is scarcely visible in the chloride that is 60 times more active than uranium, becomes strongly marked in the chloride that was enriched by fractionation until its activity was 900 times that of uranium. The intensity of this ray increases at the same time as the radioactivity, and this, we think, is a strong reason for attributing it to the radioactive part of our substance.

The various reasons which we have presented lead us to believe that the new radioactive substance contains a new element, to which we propose to give the name radium.


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Chicago: Pierre Curie and Marie Curie, "Radium," A Source Book in Physics in A Source Book in Physics, ed. William Frances Magie (Cambridge: Harvard University Press, 1935), 615–616. Original Sources, accessed December 6, 2021, http://originalsources.com/Document.aspx?DocID=HIYFNJDAGZX289A.

MLA: Curie, Pierre, and Marie Curie. "Radium." A Source Book in Physics, in A Source Book in Physics, edited by William Frances Magie, Cambridge, Harvard University Press, 1935, pp. 615–616. Original Sources. 6 Dec. 2021. originalsources.com/Document.aspx?DocID=HIYFNJDAGZX289A.

Harvard: Curie, P, Curie, M, 'Radium' in A Source Book in Physics. cited in 1935, A Source Book in Physics, ed. , Harvard University Press, Cambridge, pp.615–616. Original Sources, retrieved 6 December 2021, from http://originalsources.com/Document.aspx?DocID=HIYFNJDAGZX289A.