186 J. MOBISON : ADDRESS 



exciting temporary radio-activity in substances placed near it, 

 and this activity remains for some little time after the removal 

 of the radiiim. The explanation of this I will give presently. 



But we have not half exhausted all the wonders of radium. 

 Still greater marvels remain. 



Besides the emission of rays, radium is continually being 

 transformed into other substances, giving birth indeed to a whole 

 series of what we may look upon as separate and distinct 

 elements. A heavy gas is constantly being given off from 

 radium which has been called the " radiiun emanation." A small 

 quantity of emanation is always escaping from a radium 

 compound in its ordinary state, but it is emitted much more 

 freely when the radium is dissolved or heated. This shows that 

 a piece of radium salt in its usual condition contains a good 

 deal of emanation shut up in its interstices, which is liberated 

 on the solution or heating of the radimn. This emanation is 

 a radio-active gas of heavy atomic weight allied to the recently 

 discovered inert gases which exist in the atmosphere, such as 

 argon, helium, and neon. Radium itself, on the contrary, is 

 allied to barium, calcium, and the alkaline-earth group of 

 metals. The emanation is intensely radio-active, and with its 

 decomposition-products to be noticed later is responsible for 

 three-fourths of the activity and heat manifested by radium. 

 It has a definite spectrum of bright lines analogous to that of 

 argon. It is really a distinct element, but is not permanent, 

 continually undergoing change. Its atom is much more 

 unstable than that of radium, and breaks up at such a rate 

 that one half of the emanation is transformed into another 

 substance in about four days. It is brilliantly phosphorescent. 

 Its activity is simply enormous, being about 100,000 times 

 greater than that of radium. Its transformation is accompanied 

 by the emission of a particles, and is attended by an enormous 

 evolution of heat: the heat evolved being at least one miUion 

 times greater than that produced by any chemical reaction 

 known. Eadivini itself, freed from the emanation and its 

 subsequent products, emits only « rays ; while its activity and 

 heating effect immediately after the emanation is removed is 

 reduced to only one-quarter of its usual value. But fresh 

 emanation continues to be formed, and so the activity of the 

 radiiun continues to increase until it reaches its normal amount, 

 which occurs in about a month. 



The emanation in its turn is transformed into a solid 

 substance called by Rutherford the *' active deposit." All 



