546 SMITH'S INTERMEDIATE CHEMISTRY 



is expelled, the fact is shown by the symbols He and e, respectively. 

 The first number below each element is the average life of that 

 member of the series (y = year, d = day, h = hour, m = min- 

 ute, s = second). The second number is the atomic weight, 

 obtained by subtracting from the at. wt. of uranium (238) the 

 weight (4) of each helium atom emitted. 



Ui - He + U-Xi -- -f U-X 2 - + U 2 -*He + Ionium 

 8 X 10" y. 35.5 d. 1.65 m. 3 X 10y. 2 X 10" y. 



238 234 234 234 230 



-> He + Ra - He + Niton - He + Ra-A - He + Ra-B 



2440 y. 5.55 d. 4.3 m. 38.5 m. 



226 222 218 214 



-* 4- Ra-C - e + Ra-Ci - He + Ra-D -> + Ra-E 



28.1m. 10-* s. 24 y. 7.2 d. 



214 214 210 210 



- + Ra-F - He + Pb (end) 

 196 d. 

 210 206 



The radium emanation was shown by Ramsay to be one of the 

 inert gases (p. 296), and was renamed niton. Its density was 

 determined experimentally with a small sample, using a micro- 

 balance capable of weighing 1/500,000 mgm., and found to be 

 222.4 (density of oxygen = 32). 



The end-product of the disintegration is lead, and all uranium 

 ores contain lead (see p. 550). 



Thorium, found as phosphate in monazite sand, is also radio- 

 active and furnishes a similar series of disintegration products. 

 The final material is again lead. 



Actinium and polonium are other radioactive elements, which 

 have not yet been fully investigated. 



Transmutation of Elements; Atomic Energy. The 



phenomena of radioactivity establish the transmutation of ele- 

 ments, long regarded as a delusion of the alchemists, as an in- 



