82 THE KINGDOM OF MAN 



dissolving the salt in water, when it comes away with 

 a rush, as a gas. Sixty milligrams of bromide of radium 

 yielded to Ramsay and Soddy .124 (or about one-eighth) 

 of a cubic millimetre of this gaseous emanation. What 

 is it ? It cannot be destroyed or altered by heat or by 

 chemical agents ; it is a heavy gas, having a molecular 

 density of 100, and it can be condensed to a liquid by 

 exposing it to the great cold of liquid air. It gives a 

 peculiar spectrum of its own, and is probably a hitherto 

 unknown inert gas a new element similar to argon. 

 But this by no means completes its history, even so far 

 as experiments have as yet gone. The radium emanation 

 decays, changes its character altogether, and loses half 

 its radio-activity every four days. Precisely at the same 

 rate as it decays the specimen of radium salt from which 

 it was removed forms a new quantity of emanation, 

 having just the amount of radio-activity which has been 

 lost by the old emanation. All is not known about the 

 decay of the emanation, but one thing is absolutely 

 certain, having first been discovered by Ramsay and 

 Soddy and subsequently confirmed by independent ex- 

 periment by Madame Curie. It is this : After being 

 kept three or four days the emanation becomes, in part 

 at least, converted into helium the light gas (second 

 only in the list of elements to hydrogen), the gas found 

 twenty-five years ago by Lockyer in the sun, and since 

 obtained in some quantities from rare radio-active mine- 

 rals by Ramsay ! The proof of the formation of helium 

 from the radium emanation is, of course, obtained by the 

 spectroscope, and its evidence is beyond assail (see fig. n). 

 Here, then, is the partial conversion or decay of one 

 element, radium, through an intermediate stage into 

 another. And not only that, but if, as seems probable, 

 the presence of helium indicates the previous presence 



