56 ILLINOIS ACADEMY OF SCIENCE. 



as one of the disintegration products of radium. During the 

 seventies Crookes devised a large number of extremely interesting 

 experiments with electrical discharges through rarefied gases, and 

 laid the basis for the discovery of the Rontgen rays and many 

 of the phenomena connected with electrons and radioactivity. 



In 1889 Hillebrand in Washington discovered nitrogen in 

 uraninite and missed by only a hair's breadth the discovery of 

 argon and helium. In 1894 Rayleigh and Ramsay discovered 

 argon and shortly afterward Ramsay completed the discovery of 

 helium from terrestial materials. In 1895 Rontgen of Wiirtzburg 

 discovered the penetrating radiations from Crookes tubes. The 

 following year Becquerel in Paris discovered the Becquerel rays 

 emanated by compounds of uranium and noted the effect upon 

 photographic plates, the ionization of gases through which they 

 pass and the effect upon a screen of zinc sulphide. This led in 

 the hands of the Curies two years later to the discovery of radium. 



During the four years following Rutherford worked at McGill 

 University, partly upon radio-active thorium, which led to the 

 proposal of his disintegration theory of chemical elements, a 

 theory which has since been established on a very firm founda- 

 tion. Rutherford discovered in the course of his work that a gas 

 with the properties of one of the noble gases results from the 

 breaking down of radium. Shortly after this, in 1903, Soddy 

 who had been at work with Rutherford, and who went to the 

 laboratory of Ramsay in London to secure his aid in working out 

 the difficult problem of identifying the disintegration products, 

 succeeded in conjunction with Ramsay in establishing the fact 

 that helium results from the spontaneous decomposition of radium. 



Rutherford and others have also shown that radium as it 

 decomposes evolves a large amount of heat, one gram of radium 

 giving 118 gram calories of heat per hour. In this way chemists 

 have become acquainted with a source of energy which is enor- 

 mously greater than any form of chemical action hitherto known. 

 For instance, a given amount of radium emanation evolves during 

 its decomposition two million times as much heat as would be 

 evolved by the same quantity of electrolytic gas. 



From this time on there have been very many workers in the 

 field of radiochemistry, and it has been established that the phe- 

 nomena of disintegration is much more common than was at first 

 supposed. The rate of disintegration is measured in the period 

 required for one-half of a given element to disappear. This 



