Am.  Jour.  Pharm.  j 
November,  1919.  * 
Test  for  Sodium  Salicylate. 
745 
mass  higher  than  that  at  which  the  alkali  melts,  and  so  losing  small 
traces  by  volatilization.  Secondly,  by  neutralizing  the  alkaline  solu- 
tion with  acid,  the  colloidal  carbon  is  precipitated  so  that,  on  fil- 
tering, a  clear  water-white  solution  is  obtained.  This  is  the  method 
proposed  by  YVarington3  in  his  classic  papers  on  the  analysis  of 
commercial  compounds  of  citric  acid  and  tartaric  acid,  and  with 
slight  modifications  is  the  official  method  for  the  assay  of  alkali  salts 
of  organic  acids  of  the  Ninth  Decennial  Revision  of  the  United 
States  Pharmacopoeia,  from  which  the  following  extract  is  taken: 
"  After  allowing  the  carbonized  mass  to  cool,  disintegrate  it  with  the 
aid  of  a  stout  glass  rod  and  transfer  the  mass  and  crucible  to  a 
beaker.  Add  50  Mils,  distilled  water  and  50  Mils.  N/2  H2S04, 
cover  the  beaker  with  a  clock  glass  and  boil  for  30  minutes.  Then 
filter  the  solution  and  wash  the  residue  until  the  washings  cease  to 
redden  litmus  paper.  Now  determine  the  residual  acid  in  the  cooled 
filtrate  by  titration  with  N/2  KHO,  using  methyl  orange  as  in- 
dicator." 
In  the  case  of  sodium  salicylate,  low  results  are  obtained  by  this 
method  also,  the  carbon  retaining  a  small  portion  of  the  alkali  even 
after  prolonged  boiling  with  excess  of  standard  acid.  YVarington 
has  also  stated  that  under  some  circumstances  the  charcoal  retains  a 
little  acid,  so  that  low  results  also  would  be  caused  by  this  effect. 
To  obviate  these  errors  we  have  devised  the  following  method, 
which  gives  very  accurate  results:  About  1.5  Gm.  are  heated  to  dull 
redness  till  gases  cease  to  be  evolved,  taking  care  not  to  fuse  the 
carbonized  residue.  Detach  the  cooled  mass  from  the  crucible  as 
far  as  possible  by  means  of  a  glass  rod  and  transfer  to  a  beaker. 
Boil  gently  with  50  Cc.  distilled  water  for  at  least  five  minutes,  and 
pour  the  alkaline  solution  through  a  filter  paper,  keeping  back  as 
much  of  the  carbon  as  possible.  Boil  again  with  more  distilled 
water,  transfer  the  whole  to  the  filter  and  wash  thoroughly  with 
distilled  water.  After  draining  transfer  the  filter-paper  and  car- 
bonaceous residue  to  the  crucible,  and  ignite  at  a  dull  red  heat  until 
the  carbon  has  been  burned  completely.  Dissolve  the  residue  thus 
obtained  in  water  and  add  the  solution  to  the  filtrate  already  pre- 
pared. Now  add  excess  of  standard  acid  (say  50  Cc.  N/2  H2S04), 
cover  with  a  clock  glass,  and  heat  the  whole  to  boiling.  In  this  way 
any  colloidal  carbon  discoloring  the  solution  is  precipitated.  Filter 
again,  wash  with  hot  distilled  water  until  the  washings  cease  to 
3/.  C.  S.,  1875,  925-994- 
