THE TRANSFORMATIONS OF ELEMENTS 547 



active solution. These formed an intensely black deposit, 

 chiefly tellurium, and very active ; he named the active matter 

 radio-tellurium. Dissolved in hydrochloric acid, all the tellurium 

 was precipitated by hydrazine hydrochloride ; the active matter 

 remained in solution. By repeating the process, Marckwald 

 obtained a few milligrams of intensely active material. 



There remains the question of the final product. Radium F 

 decays at a moderately rapid rate. What becomes of it ? Two 

 lines of argument point to the conclusion that lead is formed. 

 On the assumption that the a particle is helium of atomic 

 weight 4, then, since a particles are given out by radium and 

 four of its products, the atomic weight of the final product 

 should be 226*5 — (5 x 4) = 206*5. Lead has the atomic weight 

 207, a very close agreement. 



Again, Boltwood has shown that lead is present in all 

 uranium-radium minerals, and the amount is greatest in the 

 oldest — i.e. those in which the greatest quantity of uranium 

 has disintegrated. This also points to the fact that the lead 

 is derived from uranium, and therefore from radium. 



Thorium was discovered by Berzelius in 1828. It occurs chiefly 

 in Ceylon, the recently discovered mineral thorianite containing 

 more than 70 per cent, of it. It is precipitated from solution by 

 ammonia, and usually separated in the form of oxalate. The 

 metal has been prepared as a grey powder ; it burns brilliantly 

 in air, and is easily dissolved by warm, dilute acids. The oxide 

 Th0 2 is usually obtained by calcining the oxalate or sulphate. 

 A large number of the salts have been prepared. 



An account of the disintegration changes of thorium has 

 been given in Section 1 (pp. 530-534). It need only be 

 mentioned here that the emanation is an inert gas strongly 

 resembling the gases of the argon group, while the activity 

 of radiothorium is several hundred thousand times that of 

 thorium itself. Rutherford suggests that the final disintegra- 

 tion product of thorium may possibly be bismuth. 



Actinium was discovered by Debierne in 1899, and inde- 

 pendently as emanium by Giesel in 1902 ; it is precipitated 

 with the group of cerium earths, and is closely allied to 

 lanthanum. It is many thousand times more active than 

 thorium ; although it strongly resembles that element, yet all 

 the products of the two have entirely different decay rates — 

 a sufficient proof of their separate identities. 



