CHEMICAL ELEMENTS AND ATOMS URBAIN 215 



Demarcay, who commenced the utilization of the ultra-violet 

 region for spectrochemistry, announced an element which he desig- 

 nated as :$. He later recognized the identity of this with that which 

 the spark had revealed to Lecoq de Boisbaudran, but he had some 

 reservations as to the origin of the anomalous band of Crookes, 

 He finally called the neAv element europium. He isolated it in a 

 very pure state but was unable to complete his work. 



Having had the good fortune to isolate europium almost quanti- 

 tatively, I am able to clear away some of the uncertainties relative 

 to the diverse spectrum characteristics at first observed. Particularly 

 it was apparent that the anomalous band of Crookes and the reversed 

 band of Lecoq de Boisbaudran were different manifestations of this 

 element. 



Certain that europium had been first revealed to Crookes, I sent 

 him my results before publication, together with a sample of pure 

 europium. He made a magnificent spark spectrum from the sam- 

 ple — he had much perfected his technique. He published that spec- 

 trum which had no immediate relationship with the phosphorescent 

 band and claimed nothing. 



Almost all elements have striking histories but europium would 

 have beaten all records if celtium had not been subsequently dis- 

 covered. 



I will not develop further the history of the rare earths. The 

 many elements of the group have been isolated one by one, and 

 their characteristics fixed with surety. You know as well as I, 

 my dear Brauner, the closing chapter of their history since you 

 wrote it with all the necessary detail under circumstances unfor- 

 getable to me. 



During the years which closed this history. Sir W. Ramsay 

 opened and closed a new column in the classification of Mendeleeff, 

 discovering successively the different rare gases of the atmosphere. 

 Curie and his pupils, Sir E. Rutherford and his collaborators, 

 several years later demanded from the electrometer, w^hat, until then, 

 had been asked from chemistry and spectroscopy. We know some 

 40 new radioactive elements. These we may call electrometric ele- 

 ments for we can observe the spectra only of radium and radon. 



When it was established, that the radioactive elements are born 

 and die according to exponential laws, the composite experimental 

 decay of mixtures of radioactive elements, not in equilibrium, was 

 ingeniously analyzed into the components due to the separate ele- 

 ments. Each one of these new components presumably belonged to a 

 new element. The discovery of elements in this field became thus 

 the analysis of curves. It is difficult to avoid certain scepticisms; 

 and those who have for a long while made elaborate chemical 

 analyses in order to find evidence of new chemical characters may 



