Am.  Jour.  Pharm. 
May,  1903. 
Medicinal  Manganese  Dioxid. 
215 
particularly  so  when  larger  quantities  are  prepared.  The  process 
described  is  that  proposed  by  Professor  Jannasch  (Prakt.  Leitfaden 
f.  d.  Gewichts-analyse,  1897)  as  a  quantitative  method  for  the  esti- 
mation of  manganese ;  the  composition  of  the  precipitate,  accord- 
ing to  this  authority,  is  that  of  a  hydrated  manganese  dioxid 
(Mn02.2H20).  Carnot,  who  first  suggested  the  method  (subse- 
quently worked  out  by  Jannasch),  claimed  that  the  precipitate 
formed  had  the  composition  of  Mn6On  (Bull,  de  la  Soc.  Chim.  de 
Paris  (3),  1275,  1889).  Freidheim  (Zeitschs.  f.  anal.  Ch.  38,  681, 
1899)  demonstrated  the  views  of  the  latter  to  be  incorrect,  stating 
that  if  the  precipitation  be  carried  out  in  the  presence  of  a  large 
excess  of  ammonium  salts,  the  composition  of  the  precipitate  more 
nearly  approaches  that  of  Mn02. 
According  to.  my  experiments,  the  precipitate  obtained  is  never  a 
pure  hydrated  manganese  dioxid,  but  always  contains  some  of  the 
lower  oxids,  the  percentage  of  which  in  the  final  product  depends 
largely  on  the  temperature  of  drying. 
The  method  adopted  consists  in  precipitating  the  oxid  from  a 
solution  of  manganese  sulphate,  through  the  addition  of  a  mixture 
of  ammonia  and  hydrogen  peroxid. 
For  this  purpose  250  c.c.  each  of  aqua  ammonia  (10  per  cent.)  and 
hydrogen  dioxid  (3  per  cent.)  diluted  to  the  volume  of  1,000  c.c. 
are  added,  with  constant  stirring,  to  a  solution  of  50  grammes  of 
crystallized  manganous  sulphate  (MnS044H20)  in  1,000  c.c.  of 
water.  After  washing  several  times  by  decantation,  the  precipitate 
is  then  transferred  to  a  filter  and  the  washing  continued  until  free 
from  sulphate,  and  dried  at  1500  C. 
If  the  manganese  is  poured  into  the  alkaline  solution,  the  propor- 
tion of  dioxid  produced  falls  below  43  per  cent.,  with  a  correspond- 
ing increase  in  the  quantity  of  manganoso-manganic  oxid.  The 
dioxid  in  the  dry  product  was  determined  by  means  of  standard 
oxalic  acid  and  permanganate  in  the  usual  manner,  while  the  total 
manganese  was  found  by  converting  into  the  sulphate  through  heat- 
ing with  a  slight  excess  of  sulphuric  acid,  repeating  the  operation 
until  all  of  the  oxid  has  been  converted  into  a  white  manganous 
sulphate  of  constant  weight. 
It  is  impossible  to  remove  all  of  the  water  of  hydration  of  the 
precipitated  oxid;  for  even  at  2100  C,  a  temperature  at  which  the 
precipitate  begins  to  lose  oxygen,  some  water  is  still  retained.  It 
