TRANSITION TO CLASSIFICATORY SCIENCE. 203 



markable body which, from a dark powder, is con- 

 verted into a violet-coloured gas by the application 

 of heat, was also, in 1813, the subject of a sinylar 

 rivalry between the same English and French che- 

 mists. Bromine was only discovered as late as 

 1826 ; and Fluorine, or Phtore, as, from its de- 

 structive nature, it has been proposed to term it, has 

 not been obtained as a separate substance, and is 

 inferred to exist by analogy only. These analogies 

 are very peculiar; for instance, by combination with 

 metals they form salts; by combination with hy- 

 drogen they form very strong acids ; and all, at the 

 common temperature of the atmosphere, operate 

 on other bodies in the most energetic manner. 

 Berzelius 3 proposes to call them halogenous bodies, 

 or Jialogenes. 



5. The number of Elementary Substances which 

 are at present presented in our treatises of che- 

 mistry* is fifty-three. It is naturally often asked 

 what evidence we have, that these are elementary, 

 or that they are all; how we know that new 

 elements may not hereafter be discovered, or these 

 supposed simple bodies resolved into simpler still? 

 To these questions we can only answer, by referring 

 to the history of chemistry ; by pointing out what 

 chemists have understood by analysis, according to 

 the preceding narrative. They have considered, as 

 the analysis of a substance, that elementary consti- 

 tution of it which gives the only intelligible expla- 



3 Chem., i. 262. 4 Turner, p. 971. 



