4o6 
Calcium. 
Am.  Jour.  Phara. 
June,  1920. 
were  ignited  to  constant  weight  before  a  blast  lamp  and  the  weight 
was  corrected  for  the  filter  ash. 
Results   No.  I — 99.75 
2 — 99 . 98      Av.,  99 . 86  per  cent. 
No.  5.    Precipitating  as  calcium  sulphate  and  weighing  as  such. 
0.5  Gm.  of  the  calcite  was  freed  from  silica  and  iron  and  aluminum 
oxides  as  mentioned  under  "Methods  of  Determining  Impurities." 
The  filtrate  from  the  iron  and  aluminum  oxides  was  treated  with  a 
slight  excess  of  dilute  sulphuric  acid  and  the  solution  was  diluted 
with  twice  its  volume  of  alcohol.  The  precipitate  of  calcium  sulphate 
was  allowed  to  settle  over  night,  filtered  off,  washed  thoroughly  with 
alcohol,  dried  and  ignited  separately  from  the  filter  using  only  a 
cherry-red  heat  for  ignition.  The  weight  of  ignited  CaS04  was  then 
corrected  for  filter  ash  and  calculated  to  CaCCs. 
Results   No.  I — 99  .64 
2 — 99 . 73      Av.,  99 . 68  per  cent. 
No.  6.  Precipitating  as  calcium  oxalate  and  weighing  as  calcium 
sulphate. 
A  0.5  Gm.  sample  of  the  calcite  was  treated  as  in  Method  No.  i 
to  obtain  the  calcium  oxalate  which  was  then  separated  from  the 
filter.  The  filter  was  ignited  and  the  calcium  oxalate  was  then  placed 
in  the  crucible.  A  little  10  per  cent,  sulphuric  acid  was  then  added 
to  the  contents  of  the  crucible  which  was  then  thoroughly  dried  on 
a  water  bath  and  very  carefully  ignited  with  the  cover  on,  gradually 
increasing  the  heat  until  a  cherry-red  heat  was  attained.  The  crucible 
and  contents  were  then  weighed.  The  treatment  with  sulphuric 
acid  was  repeated  until  constant  weight  was  obtained  upon  subse- 
quent weighings. 
Results   No.  I — 100.15 
2 — 100.64    Av.,  100.39  per  cent. 
No.  7.  Precipitating  as  calcium  oxalate  and  titrating  with  po- 
tassium permanganate. 
The  sample  of  calcite  was  treated  as  in  Method  No.  i  to  obtain 
the  calcium  oxalate  which  was  filtered  off,  washed  with  hot  water 
until  free  from  soluble  oxalate,  transferred  to  the  beaker  in  which 
it  was  precipitated  by  spreading  the  filter  paper  against  the  side  of 
the  beaker  and  washing  down  the  precipitate  first  with  hot  water 
and  then  with  dilute  sulphuric  acid  (25  per  cent.) ;  reserving  the  washed 
filter  by  hanging  it  across  the  edge  of  the  beaker;  50  Cc.  of  water 
