fZeXio^"""'}  Calcium.  403 
ammonia  water,  followed  by  15  Cc.  of  a  10  per  cent,  sodium  phos- 
phate solution.  The  solution  was  stirred  well  and  allowed  to  stand 
over  night.    No  weighable  amount  of  precipitate  could  be  obtained. 
MANGANKSK. 
Volhard's  reaction  (a  solution  of  0.5  Gm.  of  the  calcite  in  5  Cc. 
conct.  nitric  acid  was  boiled  with  an  excess  of  lead  peroxide,  then 
diluted  with  25  Cc.  of  water  and  the  insoluble  matter  allowed  to 
settle),  yielded  no  trace  of  violet-red  color,  therefore  it  was  concluded 
that  no  more  than  a  negligible  proportion  of  manganese  was  present, 
if  any. 
THKORKTICAL  CaCOs  CONTENT  OF  STANDARD  MATERIAIv. 
No  evidence  was  obtained  as  to  how  the  Fe203  and  AI2O3  were 
combined  in  the  calcite  but  it  was  arbitrarily  taken  that  the  two  oxides 
were  present  in  equal  proportions  and  combined  as  carbonates  in 
the  "ic"  state,  since  the  proportions  were  too  small  to  exert  any 
but  a  negligible  influence  on  the  calcium  determinations. 
Likewise  the  state  of  combination  of  the  Si02  was  not  determined, 
and  while  it  may  have  been  present  in  some  form  of  combination 
with  calcium,  yet  the  amount  concerned  would  be  negligible,  and  as 
a  consequence  the  Si02  was  arbitrarily  considered  as  being  present 
in  the  free  state. 
The  proportion  of  silica  (Si02)  was   0.0121  per  cent. 
The  proportion  of  Fe203  plus  AI2O3  was  0.0134  P^r  cent.,  which, 
figured  to  the  carbonate  state,  amounted  to   0.0286  per  cent. 
The  total  of  impurities,  therefore,  was   0.0407  per  cent. 
The  difference  between  this  figure  (0.0407  per  cent.)  and  100 
per  cent,  was  considered  to  represent  the  CaC02  content  of  the 
standard  material.  Thus,  the  CaCOs  content  was  theoretically 
99.959  per  cent. 
DETAILS  OF  THE  DIFFERENT  METHODS  OF  ESTIMATION  OF  CAIvCIUM. 
No.  I.  Precipitating  as  calcium  oxalate  and  weighing  as  cal- 
cium carbonate. 
A  0.5  Gm.  sample  was  freed  from  silica  and  iron  and  aluminum 
by  the  methods  mentioned  under  "Methods  of  Determining  Impuri- 
ties." The  calcium  was  precipitated  as  oxalate  as  mentioned  under 
"Methods  of  Determining  Impurities,"  except  that  it  was  washed 
more  thoroughly.    The  calcium  oxalate  was  dried  on  the  filter, 
