THE TRANSFORMATIONS OF ELEMENTS 



PART I— THOSE DETECTED BY RADIOACTIVE 

 METHODS; WITH SOME ACCOUNT OF THE PRO- 

 PERTIES OF THESE ELEMENTS, SO FAR AS 

 KNOWN 



By ALEXANDER T. CAMERON, M.A., B.Sc. 

 University College, London 



SECTION PAGE 



1. Methods employed in the Detection of Radioactivity : 



Thorium and its Products . 525 



2. Nature and Properties of the Radiations from Radio- 



active Elements 534 



3. Life of a Radioactive Element 538 



4. The Radioactive Elements and their Properties . . 541 



Section i. — Methods employed in the Detection of Radio- 

 activity : Thorium and its Products 



Radioactive substances are defined as those which possess 

 the property of spontaneously emitting radiations or rays capable 

 of passing through plates of metal, or other substances opaque 

 to light. The word ray was first used in a definite sense by 

 Newton, who employed it both in the sense of undulations and 

 of corpuscles, in the latter sense especially in defending the old 

 corpuscular theory of light. The rays, or radiations, emitted 

 from radioactive bodies may be in like manner either corpus- 

 cular, or consist of undulations in the ether ; both kinds are 

 known. Such radiations possess certain characteristic properties. 

 The most important are their penetrative power, emphasised in 

 the definition, their action on photographic plates, and especially 

 their property of discharging electrified bodies. The second 

 of these properties first led to their detection ; the last is the 

 means most commonly employed in their study. 



Cathode rays and Rontgen or X-rays possess such proper- 

 ties. So do the rays emitted under certain conditions by 

 zinc sulphide and similar substances. They are not produced 



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