402 
Calcium. 
Am.  Jour.  Pharm. 
June,  1920. 
The  standard  calcite  yielded  the  following  proportions  of  these 
impurities : 
Si02   0.0119 
0.0123    Av.,  0.0121  percent. 
Fe203-Al203   0.01319 
0.01360  Av.,  0.0134  per  cent. 
MgO   None 
Manganese   None 
SIIvICA. 
A  0.5  Gm.  sample  was  weighed  in  a  platinum  dish,  a  very  little 
water  was  added  followed  by  5  Co.  hydrochloric  acid  (i  :  i).  The 
mixture  was  evaporated  to  dryness  and  the  residue  baked  at  200°  C. 
until  free  from  the  odor  of  the  acid;  20  Cc.  of  i  :  i  hydrochloric 
acid  was  then  added  and  the  mixture  boiled  for  about  10  minutes; 
30  Cc.  water  was  added;  the  mixture  was  boiled  and  the  silica  col- 
lected on  a  filter  and  washed  well  with  hot  water.  The  filtrate  was 
put  through  the  same  procedure  again  but  only  an  unweighable 
amount  of  silica  was  obtained.  The  filter  containing  the  silica  was 
ignited  to  constant  weight  over  a  blast  lamp  and  weighed ;  the  weight 
of  the  silica  being  corrected  for  the  ash  of  the  filter. 
FERRIC  AND  ALUMINUM  OXIDES. 
The  filtrate  from  the  silica  was  made  alkaline  with  freshly  dis- 
tilled ammonia,  only  a  slight  excess  of  ammonia  being  used;  a  few 
drops  of  bromine  water  was  added  and  the  mixture  boiled  until  only 
a  very  faint  odor  of  ammonia  was  perceptible.  The  oxides  were 
filtered  off,  redissolved  in  hot  dilute  nitric  aid  and  reprecipitated 
with  ammonia  as  before;  they  were  then  filtered  off,  washed  thor- 
oughly with  hot  water  and  ignited  over  the  blast  a  short  time  to 
constant  weight.  The  weight  of  the  combined  oxides  was  then  cor- 
rected for  the  filter  ash. 
MAGNESIA. 
The  filtrate  from  the  ferric  and  aluminum  oxides  was  rendered 
alkaline  with  ammonia,  boiled  and  20  Cc.  of  boiling  saturated  solu- 
tion of  ammonium  oxalate  added.  The  mixture  was  boiled  for 
five  minutes  and  allowed  to  settle.  The  calcium  oxalate  was  filtered 
off  and  washed  with  hot  water  several  times,  redissolved  in  dilute 
hydrochloric  acid  and  reprecipitated  as  before.  The  filtrates  from 
the  two  precipitations  of  calcium  oxalate  were  acidified  and  evapo- 
rated to  about  150  Cc. ;  cooled  and  treated  with  17  Cc.  of  28  per  cent. 
