120 Journal of the Mitchell Society [^Jan. 



yond the range of experimentation, they were "unproductive of 

 useful results. 



And so the chemist became cautious in his definition of 

 atoms, regarding them as a series of related bodies, complex in 

 nature and hence probably divisible but indivisible by any means 

 known to him, each remaining as a unit under the influence of 

 the ordinary forces which might be applied to them. Each one 

 made itself known as a group of associated properties, or as 

 Patterson-Muir put it : " The name copper is used to distinguish 

 a certain group of properties that we always find associated to- 

 gether from other groups of associated properties, and if we do 

 not find the group of properties connoted by the term copper, we 

 do not find copper." 



The discovery by Sir William Ramsay in 1894 of argon, 

 followed in 1898 by that of neon, krypton, xenon and helium, 

 brought a new phase into the discussion. Here were atoms 

 destitute of all power of combination, even with similar atoms, 

 hence existing as monatomic gases and presenting no so-called 

 chemical properties for comparison. They formed a new group 

 in the periodic system and had to be accounted for in some way. 



It is interesting to me personally that as sectional chairman, 

 I delivered an address in 1899 before the section of chemistry 

 of the A. A. A. S. in which I spoke as follows : " Is it not fair 

 to assume that argon, helium and their companion gases, having 

 no affinity, are without electrical charge ? Were they without 

 affinity from the beginning or did they start out as ordinary 

 atoms and somehow lose this property and with it the power of 

 entering into union of any kind, even of forming molecules ? 

 Can these be the changed atoms of some of our well-known ele- 

 ments, a step nearer to the primal elements and with the elec- 

 trical charge lost ? Perhaps the coming century will unfold the 

 answer." 



The answer came much sooner than was expected. In 1903, 

 Rutherford and Soddy from the presence of helium in minerals 

 and its inability to enter into combination, suggested that it was 

 probably the product of radio-active changes. Sir William 

 Ramsay had drawn attention to the fact that helium is only 



