PHOSPHATE  OF  LIME  IN  ACETIC  ACID. 
389 
PHOSPHATE  OF  LIME  IN  ACETIC  ACID. 
To  the  Editor  of  the  American  Journal  of  Pharmacy: 
Sir, — Not  long  since,  I  had  occasion  to  determine  in  a  sample 
of  undried  Charleston,  S.  C,  guano  the  amount  of  phosphoric 
acid,  and  being  out  of  chemically  pure  acetic  acid,  I  requested 
mj  assistant  to  procure  for  me  a  small  quantity  at  No.  ,  this 
city.  Although  the  figures  of  the  first  and  second  determina- 
tions corresponded,  they  were  unsatisfactory ;  those  of  the  third, 
fourth,  and  fifth  determinations,  differing  .largely  among  them- 
selves, were  equally  unsatisfactory.  Here  follow  the  percent- 
ages :  Nos.  1  and  2,  28*69  per  cent.;  No.  3,  26*75  per  cent.  ; 
'  No.  4,  33*42  per  cent.  ;  No.  5,  30*22  per  cent. 
As  the  method  used  by  me  gives,  when  properly  executed, 
very  concordant  results,  it  was  thought  advisable  to  test  the 
chemically  pure  {!)  acetic  acid.  Ammonia  in  excess  was  added, 
when  a  copious,  white,  gelatinous  precipitate  formed,  which,  on 
investigation,  proved  to  be  phosphate  of  lime,  (The  ammonia 
filtrate  I  omitted  to  examine.  I  doubt  not  that  it  contained  lime 
originally  combined  with  carbonic  acid.)  It  is  easy  now  to 
account  for  the  high  percentages  of  phosphoric  acid,  and  to 
exphiin  the  discrepancies  the  following  is  offered : 
The  hydrochloric  or  nitric  acid  solution  of  the  guano  (prepared 
in  a  proper  manner),  to  which  a  known  quantity  of  citric  acid 
has  been  added,  is  supersaturated  with  ammonia,  the  precipitated 
bone-phosphate  of  lime  dissolved  in  an  excess  of  acetic  acid,  and 
the  lime  eliminated  by  means  of  oxalate  of  ammonia.  Now, 
according  as  the  excess  of  ammonia  is  large  or  small,  the  result 
will  be  influenced,  not  only  by  the  amount  of  acid  required  to 
saturate  an  excess,  large  or  small,  but  by  the  excess  of  acid  as 
well ;  and,  had  not  the  quantity  (1  gramme)  of  substance  used 
for  analysis  been  the  same  in  each  case,  it  would  be  natural  to 
seek  a  cause  here  ;  for  it  is  evident  the  smaller  the  amount  of 
substance  taken,  the  higher  the  percentage  of  phosphoric  acid, 
and  vice  versa. 
When  pure  acetic  acid  was  used,  the  sample  of  Charleston, 
S.  C,  guano  yielded  of  phosphoric  acid  22*36  per  cent. 
The  writer  regrets  that  he  is  unable  to  give  the  percentage  of 
