404  Calcium.  {''"'■  ^T^n^!'UT6. 
ignited  in  a  platinum  crucible  separate  from  the  filter,  to  a  faint  red- 
ness for  15  minutes  in  order  to  convert  all  of  the  oxalate  to  carbonate. 
This  ignition  may  result  in  the  formation  of  a  little  calcium  oxide, 
so,  after  weighing,  the  contents  of  the  crucible  were  moistened  with 
water  and  a  small  lump  of  ammonium  carbonate  added;  the  am- 
monium carbonate  was  driven  off  by  heating  the  crucible  on  a  water 
bath  and  the  crucible  then  ignited  to  a  very  faint  redness.  This 
treatment  was  repeated  until  constant  weight  was  obtained  and  the 
contents  of  the  crucible  no  longer  turned  red  litmus  paper. 
Results   No.  I — 99  .64 
2 — 99  .49      Av.,  99.57  per  cent.  CaCOs 
No.  2.    Precipitating  as  calcium  carbonate  and  weighing  as  such. 
A  0.5  Gm.  sample  was  freed  from  silica  and  iron  and  aluminum 
oxides  by  the  methods  outlined  under  "Methods  of  Determining 
Impurities."  The  filtrate  from  the  iron  and  aluminum  oxides  was 
treated  with  a  little  ammonia  water  and  then  ammonium  carbonate 
solution  in  slight  excess  was  added.  The  precipitated  calcium  car- 
bonate was  allowed  to  settle  for  several  hours  on  the  top  of  a  covered 
hot  water  bath;  it  was  then  filtered  off  and  washed  with  water  con- 
taining a  little  ammonia;  dried  and  ignited  separate  from  the  filter 
and  weighed  as  calcium  carbonate  as  described  under  Method  No.  i. 
Results   No.  I — 100.05 
2 — 100.10    Av.,  100.07  per  cent. 
No.  3.  Liberating  CO2  by  means  of  hydrochloric  acid  and  weigh- 
ing the  liberated  CO2  in  KOH  solution. 
The  calcite  was  placed  in  an  Erlenmeyer  containing  a  three  hole 
rubber  stopper.  Through  one  of  the  holes  a  glass  tube  was  placed. 
This  glass  tube  extended  to  the  bottom  of  the  Erlenmeyer.  The 
other  end  of  the  tube  was  connected  with  several  potash  bulbs  to 
prevent  access  of  the  CO2  of  the  air  into  the  Erlenmeyer.  The  second 
hole  of  the  rubber  stopper  contained  a  glass  tube  which  reached  just 
below  the  stopper.  The  other  end  of  the  tube  was  connected  first 
with  a  calcium  chloride  tube,  then  with  a  bulb  containing  sulphuric 
a.cid,  then  with  a  weighed  potash  bulb  followed  by  a  weighed  soda- 
lime  tube  which  was  guarded  from  the  air  by  an  unweighed  soda- 
lime  tube.  The  third  hole  in  the  stopper  of  the  Erlenmeyer  contained 
a  separatory  funnel  containing  about  twice  the  quantity  of  recently 
boiled  10  per  cent,  hydrochloric  acid  theoretically  required  to  liberate 
all  of  the  CO2  from  the  sample  of  calcite. 
