4 JOURNAL OF THE 
It was only when chemists began to realize that mere obser- 
vation of properties, chiefly physical, was not sufficient that 
the subject began to clear up and lose its vagueness. Black 
proved that certain substances were possessed of a constant 
and definite composition and fixed properties, unalterable and 
hence simple bodies or elements. Lavoisier finally cleared 
the way for the work of the nineteenth century by his defini- 
tion that ‘‘an element is a substance from which no simpler 
body has yet been obtained; a body in which no change 
causes a diminution of weight. Every substance is to be re- 
garded asan element until it is proved to be otherwise.” 
With this clear definition to build upon, a rational system of 
chemistry became, for the first time, a possibility. 
Thus the elements were recognized as simple bodies be- 
cause there were no simpler. They were not complex or com- 
pound. ‘This distinction was clearly drawn between bodies 
simple and bodies compound, and the name simple body has 
been frequently used as a synonym for element through a 
large part of this century. Naturally the question of simplic- 
ity was first settled by an appeal to that great arbiter of 
chemical questions, the balance. And, quite as naturally, 
many blunders were made and the list of bodies erroneously 
supposed to be simple was very large. All whose weight 
could not be reduced were considered elementary. When, 
however, from stich a body, something of lesser weight could 
be produced, its supposed simplicity was, of course, dis- 
proved. 
This test for the elemental character has been clung to per- 
sistently, and is perhaps still taught, although it was long ago 
recognized that many of the elements existed in different 
forms, a pheriomenon to which Berzelius gave the name a//o- 
tropism. One only of these could be the simplest, and the 
others could be reduced to this one and rendered specifically 
lighter. With the discovery of this relation it should have 
been quite apparent that the old definition would no longer 
hold good. But many years passed before chemists were 
made to feel that a new definition was necessary, and adapted 
one to the newer knowledge. 
