Am.  Jour.  Pharm. 
June,  1920. 
Calcium. 
405 
The  assay  was  made  as  follows:  Air  was  drawn  for  about  15 
minutes  through  the  apparatus  by  means  of  an  aspirator  attached 
to  the  soda-lime  guard  tube,  thus  the  air  entered  the  train  of  potash 
bulbs  and  was  depleted  of  CO2,  it  then  entered  the  Erlenmeyer  con- 
taining the  sample  and  then  in  turn  the  calcium  chloride  tube  and 
sulphuric  acid  bulb  which  depleted  it  of  moisture.  The  air  then 
entered  the  weighed  potash  bulb  from  which  it  took  up  some  moisture 
and  which  it  then  deposited  in  the  weighed  soda-lime  tube  which  was 
guarded  against  the  moisture  and  the  CO2  of  the  air  and  aspirator, 
by  the  un weighed  soda-lime  tube  at  the  end  of  the  train.  The 
weights  of  the  weighed  potash  bulb  and  soda-lime  were  then  obtained 
and  any  variation  from  their  previous  weights  was  noted.  The 
weighed  potash  bulb  and  soda-lime  tube  were  replaced  in  the  train, 
the  current  of  the  air  was  re-established  and  the  10  per  cent,  hydro- 
chloric acid  in  the  separatory  funnel  was  allowed  to  drip  into  the 
Erlenmeyer  where  it  came  into  contact  with  the  calcite  and  liberated 
CO2  which  was  dried  by  passing  through  the  calcium  chloride  tube 
and  sulphuric  acid  bulb  and  then  caught  by  the  weighed  potash  bulb 
and  soda-lime  tube.  The  air  was  allowed  to  pass  for  15  minutes, 
during  which  time  the  contents  of  the  Erlenmeyer  were  stirred  up 
by  the  current  of  air  and  warmed  a  trifle  by  external  heat.  The 
weighed  potash  bulb  and  soda-lime  tube  were  then  allowed  to  stand 
in  the  balance  case  for  about  1 5  minutes  and  weighed.  When  not 
connected  in  the  train,  the  ends  of  the  weighed  potash  bulb  and  soda- 
lime  tube  were  kept  closed  by  small  rubber  nipples  which  were  re- 
moved momentarily  and  then  replaced  before  each  weighing  in  order 
to  insure  absence  of  pressure  or  vacuum  within  the  bulb  and  tube. 
The  increase  in  weight  of  the  potash  bulb  and  tube  corrected  as  found 
necessary  by  the  blank  was  considered  to  be  due  to  the  CO2  from  the 
calcite  and  was  calculated  into  terms  of  CaCOs. 
Results   No.  I —  99-57 
2 — 100.50    Av.,  100.03  per  cent.  CaCOs 
No.  4.  Precipitating  as  calcium  oxalate  and  weighing  as  cal- 
cium oxide. 
In  all  respects  this  method  was  similar  to  No.  i  with  the  excep- 
tion that  the  calcium  oxalate  after  gentle  ignition  was  made  into  a 
paste  with  water  and  spread  around  the  sides  of  the  crucible  so  that 
the  calcium  oxide  would  be  obtained  in  a  very  thin  layer.  This  was 
found  essential  because  of  the  tenacity  with  which  calcium  carbonate 
retains  its  carbon  dioxide.    Finally  the  crucible  and  its  contents 
