SCHEELE  AND  HIS  DISCOVERIES. 
53 
bodies  could  bring  it  back  to  the  state  of  White  Arsenic,  and 
even  of  Metallic  Arsenic.  On  heating  it  in  combination  with 
Ammonia,  he  obtained  a  gas  which  extinguished  flame,  being 
neither  fixed  air  nor  Carbonic  Acid.  This  wa3  Nitrogen.  La- 
voisier and  Berthollet  repeated  his  experiments,  and  easily  ex- 
plained the  various  phenomena  described  by  the  principles  of 
the  new  theory  of  Chemistry.  Never  weary  of  his  labors, 
Scheele  worked  on  Quartz,  Silica,  Clay,  and  Alum ;  then  he 
commenced  his  Analysis  of  Benzoar,  in  which  he  discovered  a 
particular  acid,  first  called  Lithic,  and  afterwards  Uric  Acid. 
These  researches  paved  the  way  for  all  the  recent  investiga- 
tions of  Urinary  Calculi,  and  even  of  Urine  itself. 
The  same  year  Scheele  obtained  Oxalic  Acid  by  the  action  of 
Nitric  Acid  on  Sugar.  In  1777  appeared  his  treatise  on  Air 
and  Fire,  a  work  on  which  he  had  been  long  engaged.  Whether 
or  not  he  may  claim  to  have  been  one  of  the  original  discoverers 
of  Oxygen  is  uncertain,  yet  in  this  identical  pamphlet  occurs  the 
capital  experiment  that  when  Manganese  is  exposed  to  a  high 
degree  of  temperature  and  then  heated  with  Sulphuric  Acid,  an 
elastic  fluid  is  disengaged,  which  he  named  Air  of  Fire.  Priestly 
had  in  truth  announced  the  same  fact  in  1774,  and  Scheele,  un- 
fortunately for  himself,  only  published  his  discovery  when  his 
work,  which  had  been  seven  years  in  preparation,  was  complete. 
He  established  also  the  point  that  common  air  is  composed  of 
Air,  of  Fire  and  Foul  Air  (Nitrogen)  ;  that  the  process  of  com- 
bustion deprives  common  air  of  its  purest  part  (Oxygen).  The 
same  work  contains  remarks  of  the  greatest  interest  on  Nitrous 
Gas,  on  Sulphuretted  Hydrogen,  on  Fulminating  Gold,  and  on 
the  Radiation  of  Heat. 
In  the  course  of  1778  this  wonderfully  industrious  man  pub- 
lished four  separate  memoirs  ; — 1.  A  process  for  preparing  Cal- 
omel. 2.  The  preparation  of  the  Oxychloride  of  Antimony.  3. 
The  preparation  of  what  is  still  called  Scheele's  Green,  which 
was  obtained  on  pouring  a  solution  of  Potash  and  white  Arsenic 
in  a  solution  of  Sulphate  of  Copper.  It  is  an  Arsenite  of  Cop- 
per. 4.  Molybdenum,  whose  ore  was  originally  confounded  with 
Plumbago;  Scheele  proved  that  it  was  a  compound  of  Sulphur 
and  a  whitish  powder  (Molybdic  Acid),  from  which  more  recently 
Hielm  extracted  Molybdenum  in  a  state  of  Metal.    In  1779  he 
