AmMayri9^8arm* 5  Preparation  of  Permanganate  Solutions.  '  359 
example,  in  the  estimation  of  calcium  as  oxalate  in  small  portions  of 
biological  fluids2  where  permanganate  solutions  approximately 
N/100  must  be  used,  the  elimination  of  these  sources  of  error  is  a 
necessity. 
Where  a  standard  permanganate  weaker  than  N/10  was  desired 
it  has  been  customary  to  make  this  shortly  before  using  by  dilution 
of  a  stronger  permanganate  solution,3  in  spite  of  the  fact  that  ordi- 
nary distilled  water  contains  appreciable  amounts  of  organic  matter 
which  can  be  removed  only  with  great  difficulty.  For  instance,  we 
have  found  that  water  redistilled  from  both  acid  and  alkaline  per- 
manganate may  still  cause  an  appreciable  deterioration  (as  much  as 
2  or  3  per  cent.)  when  used  in  diluting  permanganate  from  N/10 
to  N/100.  This  was  true  even  where  the  weak  solution  was  used 
at  once.  If  allowed  to  stand  for  any  length  of  time,  or  if  less  care- 
fully distilled  water  was  used,  the  permanganate  was  almost  entirely 
decomposed,  this  process  being  hastened  by  the  catalytic  action  of 
the  oxides  of  manganese  which  were  formed. 
To  avoid  the  inconvenience  as  well  as  inaccuracy  of  dilution  we 
have  endeavored  to  prepare  permanent  N/100  solutions.  The  prin- 
ciple used  is  not  new,  but  the  technique  as  we  have  adapted  it  and 
some  data  pertaining  to  the  keeping  qualities  of  dilute  permanga- 
nates and  of  oxalic  acid  solutions  used  as  standards  may  be  of  in- 
terest. 
Preparation  of  N/100  Potassium  Permanganate. 
Dissolve  0.04  Gm.  pure  potassium  permanganate  crystals  in.  one 
liter  of  redistilled  water  in  a  thoroughly  clean  Florence  flask  which 
has  been  rinsed  with  the  same  water.  Digest  at  or  near  the  boil- 
ing point  for  36  hours.  A  funnel  covered  with  a  watch-glass  may 
be  used  as  a  reflux  condenser.  Cool  and  allow  to  stand  over  night. 
Without  disturbing  the  sediment  of  manganese  oxides,  filter  with 
gentle  suction  through  a  3-in.  Biichner  funnel  lined  with  ignited 
asbestos.  Both  funnel  and  filter  flask  should  be  rinsed  with  re- 
distilled water.  Transfer  the  permanganate  solution  to  a  glass- 
stoppered  bottle  free  from  traces  of  organic  matter.  The  solution 
should  be  kept  in  the  dark  when  not  in  use.    If  the  asbestos  be- 
2Halverson  and  Bergeim,  /.  Biol.  Chem.,  24  (1916),  22;  29  (1917),  337; 
Halverson,  Mohler  and  Bergeim,  /.  Am.  Med.  Assn.,  68  (1917),  1309. 
3  See  Michaelis,  Biochem.  Z.,  59  (1914),  166,  and  Ellinger,  Z.  physiol. 
Chem.,  38  (1903),  192,  for  example. 
