54 
SCHEELE  AND  HIS  DISCOVERIES. 
continued  the  same  subject,  and  showed  in  what  manner  Plum- 
bago differed  from  Molybdic  Acid,  demonstrating  that  it  was  com- 
posed of  fixed  air  and  Carburet  of  Iron.  This  analysis  was  fol- 
lowed by  Experiments  on  the  quantity  of  pure  air  contained  in 
the  atmosphere.  For  a  year  he  continued  his  observations  and 
obtained  the  same  results  as  Lavoisier,  namely,  that  pure  air 
(Oxygen)  formed  393d  part  of  our  atmosphere.  About  the  same 
time  appeared  his  "  Experiments  on  the  Decomposition  of  Neu- 
tral Salts  by  Quick  Lime  and  Iron." 
In  the  Annals  of  the  Academy  of  Stockholm,  are  three  pub- 
lished Memoirs  belonging  to  1780.  A.  Remarks  on  Fluor  Spar, 
being  chiefly  an  answer  to  objections  to  his  previous  paper.  B. 
Examination  of  Milk  and  its  Acid.  After  having  stated  the  in- 
fluence of  Alkalis  and  Acids  in  determining  its  coagulation,  he 
pointed  out  that  caseine,  when  calcined,  contained  Phosphoric 
Acid  and  Lime.  In  order  to  obtain  the  Acid  of  Milk,  he  evapo- 
rated the  Serum  down  to  an  eighth  part,  saturated  it  with  quick- 
lime, which  he  afterwards  separated  by  Oxalic  Acid ;  then  he 
treated  the  Liquor  with  Alcohol,  which  dissolved  the  Lactic  Acid 
without  touching  the  Sugar  of  Milk.  On  distilling  the  Alcohol 
he  obtained  pure  Lactic  Acid.  C.  The  examination  of  Sugar 
of  Milk.  On  treating  the  concentrated  Serum  with  Nitric  Acid 
he  obtained  Saccho-lactic  Acid  in  crystals,  or  in  the  form  of  a 
white  powder,  sparingly  soluble  in  water,  and  forming,  with  al- 
kalis, crystallizable  salts.  Each  succeeding  year  is  the  record 
of  some  new  and  original  observation  ;  but  we  must  not  linger 
too  long  over  details. 
In  1781  appeared  the  Memoir  on  Tungsten  and  his  discovery 
of  Tungstic  Acid.  In  1782  three  new  memoirs  saw  the  light, 
the  first  being  Observations  on  Ether,  and  the  second,  A  Method 
for  Preserving  Vinegar ;  the  third,  same  date,  is  an  Essay  on 
the  Coloring  Matter  of  Prussian  Blue.  This  is  one  of  his  most 
important  dissertations,  and  probably  his  chef  a"  ceuvre.  It  is 
divided  into  two  parts.  In  the  first,  Scheele  endeavors  to  dis- 
cover the  substance  which,  in  Prussian  Blue,  is  united  with  Iron 
and  an  alkali.  The  methods  employed  in  this  research  are  most 
ingenious,  and  show  the  utmost  skill  in  the  employment  of  re- 
agents. By  dint  of  repeated  trial,  he  succeeded  in  discovering 
the  coloring  matter ;  his  first  description  of  it  being  that  it  pos- 
