Am.  Jour.  Pharm.  ) 
June,  1920.  J 
Calcium. 
407. 
was  then  added  followed  by  10  Cc.  of  concentrated  sulphuric  acid; 
the  solution  was  heated  just  to  boiling  and  then  titrated  to  the  first 
pink  change  with  0.1  N  potassium  permanganate;  then  the  filter 
paper  was  dropped  in  causing  the  pink  color  to  be  discharged  owing 
to  the  trace  of  oxalate  still  present  in  the  paper  and  finally  the  end 
point  was  obtained  by  a  few  drops  of  the  0.1  N  potassium  perman- 
ganate. The  permanganate  was  standardized  against  calcium 
carbonate  obtained  from  the  standard  calcite  as  in  Method  No.  2. 
This  calcium  carbonate  was  considered  as  being  100  per  cent.  CaCOs. 
The  method  of  standardization  was  as  follows : 
A  weighed  portion  of  the  freshly  ignited  CaCOa  (free  from  CaO) 
was  dissolved  in  hydrochloric  acid  and  precipitated  as  calcium  oxa- 
late as  mentioned  under  "Methods  of  Determining  Impurities," 
and  this  calcium  oxalate  was  dissolved  in  sulphuric  acid  (25  per  cent.) 
and  hot  water  as  mentioned  a  few  lines  above  and  the  permanganate 
solution  run  in  to  the  end  point,  including  the  few  additional  drops 
required  by  adding  the  washed  filter  upon  which  the  oxalate  was 
collected,  to  the  titrated  liquid. 
Results   No.  I — 99.91 
2—  99.46 
3—  99.90 
4 —  99.47     Av.,  99.68  per  cent. 
No.  8.  Precipitated  as  calcium  oxalate  from  a  slightly  acid 
solution. 
A  0.5  Gm.  sample  of  the  calcite  was  dissolved  directly  in  dilute 
hydrochloric  acid;  the  solution  was  diluted  to  150  Cc.  and  made 
barely  alkaline  with  freshly  distilled  ammonia;  a  hazy  precipitate 
of  ferric  and  aluminum  hydroxides  resulted;  hydrochloric  acid  was 
added  drop  by  drop  until  acid,  then  2  drops  in  excess  was  added. 
The  mixture  was  then  boiled  and  the  calcium  totally  precipitated 
as  calcium  oxalate  by  means  of  an  excess  of  ammonium  oxalate  solu- 
tion. The  precipitated  calcium  oxalate  was  allowed  to  settle  and 
was  then  filtered  off  and  titrated  with  o.i  N  potassium  permanganate 
as  in  Method  No.  7. 
Result   99.82  per  cent.  CaCOs 
The  experiment  was  repeated  using  acetic  acid  to  dissolve  the 
calcite  and  adding  2  drops  of  acetic  acid  in  excess  before  precipitating 
with  ammonium  oxalate. 
Result 
99.91  per  cent.  CaCOa 
