RADIUM. « 



By E. Curie, 

 Professeur a la Fdcnllr deit Scienci'x dr I' Jhiircrsiff dr Paris. 



]\I. Becfiuorel discovered in ISlx; that uraniimi and its products emit 

 spontaneously radiations which, like the Kontgen rays, are photo- 

 graphically active, augment the electrical conductivity of the air 

 through which the>' pass, traverse black paper and thin sheets of metal 

 freel}^ hnt can neither be reflected nor refracted/' 



Compounds of thorium emit radiations analogous in their proper- 

 ties, and of comparable intensity/ The radiations thus spontaneously 

 emitted by certain substances received the name "Becquerel rays," 

 and we are accustomed to speak of the substances emitting them as 

 radio-active. 



Madame Curie and myself have discovered new radio-active sub- 

 stances existing in minute quantities in certain minerals, but possess- 

 ing the property of radio-activity in a ver}" high degree. We have 

 separated the radio-active substance polonium, analogous to bismuth 

 in its chemical reactions, and radium'' which more resembles barium. 

 M. Debierne has since separated actinium, which is a radio-active sub- 

 stance to be classed chemically with the rare earths.' 



Polonium, radium, and actinium emit radiations of an order of inten- 

 sity a million times higher than those emitted by uranium and thorium, 

 and have enabled physicists ta conduct many investigations of the 

 phenomena of radio-activity within the past few years. The present 

 j)aper is contined to the description of radium, which we have proved 

 to be a new element, and have succeeded in isolating in the form of a 

 pure salt.' This is the substance which has been most widely used in 

 researches on radio-activity. 



« Translated from a lecture delivered by Prof. E. Curie before the Royal Institu- 

 tion of London, as printed in the Revue Scientifique February 13, 1904. 



''Ik'cqnerel, Comptes rendns de 1' Academic des Sciences, 185)6 and 1897. Ruther- 

 ford, Phil. Mas-, 1899. 



"^Schmidt, Wied. Ann., Band 65, p. 141. Rhulame Curie, Comptes rendus de 

 I'Acadenne des Sciences, April, 1898. 



'' Discovt'red in an investigation shared with M. Bemont. 



>■ P. Curie and Mme. Curie, C. R. de 1' Academie des Sciences, .July, 1898. P. Curie, 

 Mme. Curie, and M. Bemont, C. R., December, 1898. Debierne, C. R., October, 

 1899, and April, 1900. 



/Mme. Curie. These ;i la Facultc des Sciences de Paris, 1903. 



187 



