WHAT IS AN ELEMENT ? 155 



It will be noticed that their atomic weights lie between 

 those of the elements in* the vertical rows ; and that they 

 separate the active elements of the fluorine group from 

 the equally active elements of the sodium group. 



The discovery of these elements, however, has added 

 little to our knowledge as regards the nature of elements in 

 general, except in so far as to show that elements which 

 form no compounds can exist. It might be supposed that 

 the same agencies which are successful in splitting up 

 compounds into the elements of which they consist might 

 decompose elements into some still simpler substances ; 

 of course the elements thus decomposed could no longer 

 be called elements. And it appeared not impossible that 

 in a series of elements closely resembling each other, like 

 those of the sodium column, or the chlorine column, it 

 might be impossible to decompose those of higher atomic 

 weight into those of lower atomic weight, and perhaps 

 something else. Such agencies are : a high temperature 

 or an electric current. Water, for instance, can be decom- 

 posed into hydrogen and oxygen either by heating steam 

 to whiteness or by passing an electric current through 

 water. But it is needless to say that the elements have 

 been repeatedly exposed to the highest temperature and 

 to the strongest electric currents and yet have remained 

 elements. There are, indeed, reasons for supposing that 

 at the enormously high temperatures of the sun and of 

 the fixed stars some of our elemei|j are decomposed ; but 

 it has hitherto been impossible to reproduce such extreme 

 conditions on the earth. 



The element carbon is characterised by the enormous 

 number of compounds which it forms, chiefly with hydrogen 

 and oxygen, although many other elements can be in- 

 duced to combine with it. And one instructive fact is 

 to be noticed as regards such compounds : the greater the 

 number of atoms they contain the more easily they are 



