AAuiustr'  fgil"11')     Romance  of  Chemical  Elements.  569 
metals,  and  which  he  called  "inflammable  air."  Later,  in  1781,  he 
showed  that  by  burning  of  this  gas,  water  was  produced  and  from 
this  fact  the  name  is  derived  from  the  Greek  v&wp,  hydros,  =  water, 
and  yewaw,  gennao,  =  to  produce.  There  is  evidence  that  the  al- 
chemists knew  of  hydrogen,  without  examining  it  closer,  for  Para- 
celsus (1493-1541)  mentions  that  a  combustible  gas  is  produced 
by  treating  certain  metals  with  acids,  and  in  1700  Lemary  recog- 
nized knallgas,  the  explosive  mixture  of  hydrogen  and  air.  Liquid 
and  solid  hydrogen  was  for  the  first  time  prepared  by  Dewar  in  1! 
Nitrogen. 
In  1772  Rutherford  showed  that  only  a  part  of  the  air  could  be 
used  for  breathing,  and  that  the  remainder  could  not  be  used  for 
combustion.  This  he  termed  "  mephisticated  air."  Priestley  termed 
it  "  phlogisticated  air,"  and  Cavendish  in  1785  produced  nitric  acid 
by  passing  electric  sparks  through  moist  air,  thus  proving  that  nitric 
acid  can  be  produced  from  air.  He  gave  the  gas  the  name  nitrogen, 
from  niter  and  gennao,  produce,  meaning  the  niter-producing  gas 
(niter  =  saltpeter  or  potassium  nitrate). 
Oxygen. 
But  the  most  important  of  all  these  discoveries  was  that  of  oxy- 
gen, isolated  on  the  first  of  August,  1774,  by  J.  Priestley  (1733- 
1804)  by  heating  mercuric  oxide.  K.  W.  Scheele  (1742-1786), 
working  independently,  also  isolated  in  1775  the  gas,  which  he  called 
"empyreal  air,"  but  it  was  A.  L.  Lavoisier  (1 743-1 786)  who  devel- 
oped the  new  theory  of  combustion  and  termed  the  gas  oxygen,  be- 
cause he  found  that  many  of  its  combustion  products  were  acids, 
from  the  Greek  o£u?,  oxy,  =  sour,  and  yewaw,  gennao,  =  produce. 
Chlorine. 
Chlorine  was  discovered  by  Scheele  in  1774  and  called  "de- 
phlogisticated  muriatic  acid."  Berthollet  in  1784  regarded  it  as 
"oxygenized  muriatic  acid"  and  in  1809  Sir  Henry  Davy  finally 
gave  it  the  name  chlorine  from  the  Greek  x^0/00'5?  chloros,  =  yellow- 
ish green,  on  account  of  its  color. 
