CHAPTER IV. 



RADIUM. 



Radium has never been isolated. As a free element it has 

 never been seen, never been touched, never been handled, as 

 gold and iron may be, but it is manifest in the properties of 

 its compounds. It has been studied only in combination 

 with other elements, chiefly in the form of the chloride or 

 bromide. We know that it exists as an element different 

 from any other body in nature, solely and completely through 

 the fact that every element has had its own sign manual, or 

 spectrum, by means of which it signifies its existence, 

 whether it is found in the sun, the stars or the laboratory. 

 Fig. 25 is the spectrum of radium as obtained byM.Demarcay 

 from a small quantity of chemically pure radium chloride 

 provided by Professor Curie. The lines numbered at the top 



Fig. 25. Comparative spectra of radium and calcium. 



of the picture are caused by no known element on the earth 

 or in the heavens. Therefore radium is a new element. 



(93) 



