OLD AND NEW ALCHEMY 265 



have learned little more than that some or all of the various 

 forms of matter spontaneously decay, and give rise, in 

 decaying, to other forms. The three heaviest metals, uran- 

 ium, thorium, and radium, are the most conspicuous possess- 

 ors of these extraordinary properties. Their intimate 

 structure is such as to render them unstable. Each of 

 their atoms is the seat of eventually self-destructive activi- 

 ties. True, their waste, although unceasing, is excessively 

 slow. Radium, the shortest-lived of the trio, needs about 

 1,300 years, Professor Rutherford calculates, 1 to become 

 half disintegrated, while 30,000 must elapse before the 

 earth's present stock is virtually exhausted. Something 

 will, indeed, be left; but it will not be radium. Perhaps 

 the residuum will prove to be lead. Indications have been 

 gathered that radium is compounded, in a transcendental 

 manner, of helium and lead. Helium unquestionably 

 escapes at each stage of its decay, and the conjecture is 

 plausible that, after the fifth and last emission of helium- 

 particles, lead remains as a caput mortuum. 



Nor is radium itself believed to be an aboriginal sub- 

 stance. For unless there were a continuous source of sup- 

 ply, the stock would evidently have long ago become- 

 exhausted. What perishes day by day must day by day 

 be renewed, and the renewal is, in this case, apparently 

 effected by the exorbitantly slow transformation of uran- 

 ium. The grounds for this view are: First, that the two 

 metals never occur separately, uranium always holding a 

 percentage of radium; secondly, that this percentage has 

 a constant value. Its invariability clearly results from the 

 establishment of an equilibrium between production and 

 waste. Radium is scarce, because it is quickly dissipated. 

 It bears within itself the seeds of destruction. Solid in 

 appearance, it is in reality more unstable than the thinnest 

 air. Even the substantial preservation of its materials 

 is open to doubt. In other words, there is some proba- 

 bility that many of the particles flung out from its dis- 

 io- Active Transformations, page 176. 



