.Am.  Jour.  Pharin. 
April,  1892. 
Sodium  Benzoate. 
185 
SODIUiM  BENZOATE. 
By  Henry  F.  Kaercher. 
Contribution  from  the  Chemical  Laboratory  of  the  Philadelphia  College  of  Pharmacy, 
No.  106. 
Read  at  the  Pharmaceutical  Meeting,  March  15. 
This  salt  is  regarded  by  our  Pharmacopoeia  as  crystallizing  with 
a  definite  amount  of  water — i.  e,,  one  molecule  or  1 1  *  1 1  per  cent. 
The  result  of  an  investigation  by  the  writer,  however,  indicates  that 
it  contains  variable  quantities  of  water,  which  may  be  entirely 
removed  at  a  low  temperature. 
The  first  specimen  examined  was  a  sample  of  the  salt  as  found  in 
the  market.  It  corresponded  to  all  the  tests  of  purity.  On  heating 
a  portion  to  2000  C,  it  was  found  that  this  temperature  was  not 
sufficiently  high  to  decompose  it.  The  amount  of  moisture 
obtained  by  drying  to  constant  weight  at  1200  C.  was  4-59  per 
cent.  Several  methods  were  used  to  determine  whether  this  dried 
salt  was  anhydrous  or  not — one  by  igniting  and  estimating  the  ash 
volumetrically  as  sodium  carbonate;  the  other  by  estimating  the 
benzoic  acid.  The  latter  process  was  found  to  give  the  more 
accurate  results  and  was  accomplished  by  treating  an  aqueous  solu- 
tion of  the  salt  with  dilute  hydrochloric  acid,  shaking  out  the  pre- 
cipitated benzoic  acid  with  ether,  and  allowing  the  solvent  to 
evaporate  spontaneously.  The  residue  on  being  weighed  gave 
84-66  per  cent,  (the  theoretical  amount  in  an  anhydrous  salt  being 
8472  per  cent.). 
The  next  salt  examined  was  made  by  granulating  at  6o°  C. 
Estimation  of  the  moisture  gave  18-23  per  cent.  The  same  salt 
crystallized  from  alcohol,  however,  gave  only  9  0 1  per  cent.  (1  rj  I 
per  cent,  being  the  theoretical  amount  of  one  molecule),  all  of 
which  was  removed  at  120°  C. 
An  anhydrous  salt  was  obtained  by  keeping  a  small  quantity  of 
that  crystallized  from  alcohol,  in  a  desiccator  over  sulphuric  acid 
.for  several  days. 
Another  sample  was  made  by  crystallizing  from  aqueous  solution, 
displacing  adhering  water  by  washing  first  with  alcohol  and  then 
with  ether,  and  exposing  to  the  air  for  a  short  time.  This  was 
found  not  to  be  a  practical  method. 
A  salt  was  then  made  from  benzoic  acid  sublimed  from  benzoin, 
by  granulating  at  a  moderate  heat  (below  2000  C).   In  this  prepara- 
