744 
Test  for  Sodium  Salicylate. 
/Am.  Tour.  Pharm. 
<•  November,  19 19. 
NOTE  ON  THE  QUANTITATIVE  B.P.  TEST  FOR  SODIUM 
SALICYLATE.1 
By  J.  B.  P.  Harrison,  F.I.C.,  and  F.  E.  Carter,  B.Sc. 
The  monograph  of  the  British  Phamacopoeia  states  that  sodium 
salicylate  must  contain  99.5  per  cent,  of  the  pure  salt. 
The  quantitative  test,  as  given  in  the  paragraph  headed  "  Char- 
acters and  Tests,"  is  thus  described :  "  2  Cms.  heated  to  redness  till 
gases  cease  to  be  evolved  leave  an  alkaline  residue  which,  when 
treated  with  water,  filtered,  and  well  washed,  yields  a  clear  solution 
requiring  for  neutralization  not  less  than  24.8  milliliters  of  N/2 
solution  of  sulphuric  acid."  This  is  practically  the  same  test  as  that 
prescribed  for  quantitatively  determining  sodium  and  potassium  tar- 
trate, but  whereas  in  this  instance  very  accurate  results  can  be  ob- 
tained, in  the  case  of  sodium  salicylate  varying  results  are  given  by 
different  experiments  on  the  same  sample. 
F.  H.  Alcock,2  in  a  paper  entitled  "  Sodium  Salicylate,"  has 
drawn  attention  to  this  anomaly,  and  attributed  the  unsatisfactory 
results  obtained  by  titrating  the  alkaline  solution  after  treating 
sodium  salicylate  in  the  manner  above  described  to  the  retention  of 
part  of  the  alkali  by  the  carbonaceous  matter  which  is  filtered  off, 
even  after  this  has  undergone  very  considerable  washing  with  dis- 
tilled water.  This  fact  we  can  fully  confirm,  and  at  the  end  of  this 
note  shall  give  results  in  confirmation.  Alcock,  however,  did  not 
concern  himself  with  improving  the  details  of  the  method,  but  put 
forward  a  new  process  based  on  the  decomposition  of  sodium  sali- 
cylate by  ammonium  chloride  when  the  two  are  heated  together  in 
strong  aqueous  solution. 
One  of  the  disadvantages  of  the  alkalimetric  process  as  described 
in  the  B.  P.  is  that  the  solution  obtained  for  titration  with  standard 
acid  is  often  deeply  colored  with  carbonaceous  matter,  so  that  it  is 
difficult  to  see  the  change  in  color  of  the  indicator  at  the  end  of  the 
reaction.  This  tendency  to  produce  a  solution  of  colloidal  carbon 
can  be  obviated  in  two  ways.  Firstly,  by  prolonged  ignition  of  the 
carbonized  mass  whereby  the  carbon  is  either  burned  away  or  ren- 
dered in  a  form  denser  than  that  of  colloidal  carbon.  In  thus  heat- 
ing, however,  there  is  a  danger  of  raising  the  temperature  of  the 
1  Reprinted  from  The  Pharm.  Jour,  and  Pharmacist,  Sept.  13,  1919. 
2  P.  J.,  Fourth  Series,  Vol.  23,  p.  597. 
