Am'jSyr'i9ih9.rm'       Purity  of  Commercial  Aspirin.  469 
or  in  the  tablet-bottle  in  the  waistcoat  pocket — yet  capable  of  imme- 
diate disintegration  in  water.  In  the  "  standard  "  series  mentioned 
above  all  the  samples  were  very  satisfactory  in  this  respect.  On 
dropping  the  tablets  into  water  and  allowing  them  to  remain  for 
half  a  minute  without  agitation  some  "  effloresced  "  into  a  powder, 
others  swelled  and  parted,  and  all  save  one  became  powder  on 
swirling  the  test-glass  ;  the  exception  remained  partially  powdered, 
about  half  the  tablet  retaining  its  form,  yet  being  quite  soft  and  dis- 
solving within  a  minute  or  two.  In  this  connection  it  is  interesting 
to  note  what  must  indicate  variability  in  machining,  which  must 
occur,  for  on  taking  six  or  eight  tablets,  as  was  done  with  one 
brand,  about  half  of  them  disintegrated  within  ten  seconds,  the  re- 
mainder taking  the  full  half-minute. 
Analytical  Precautions. 
In  the  examination  of  tablets  certain  precautions  are  necessary 
on  account  of  the  excipient,  which,  apart  from  the  usual  starch,  talc 
and  adhesives,  sometimes  includes  small  quantities  of  a  wax  or  fatty 
substance.  Stearic  acid  has  been  noted  in  one  or  two  cases,  and  if 
this  and  substances  such  as  Japan  wax  are  employed  it  is  clear  that 
for  very  precise  work  analytical  procedure  must  be  modified  to  meet 
them.  A  determination  of  the  free  salicylic  acid  by  iron  and  the 
total  by  bromine  is  perhaps  the  most  satisfactory  means  of  evalua- 
tion. In  the  latter  test  it  is  best  to  extract  the  tablet  with  alcohol 
and  filter ;  add  alkali  and  distil  off  the  alcohol  during  saponification, 
then  follow  the  method  indicated  in  the  case  of  aspirin. 
For  the  free  salicylic  acid,  crushing  the  tablet  and  applying  the 
B.P.  test  is  not  of  much  value  where  fatty  excipients  have  been  used 
since,  while  really  containing  quite  the  ordinary  traces,  the  barest 
evidence  is  given  in  the  water  test.  'For  the  estimation  it  is  best  to 
take  one,  two,  or  three  tablets,  grind  up  in  a  mortar  with  9  Cc.  of 
alcohol  and  a  little  kaolin,  adding  70  Cc.  of  water,  and.  drawing 
through  a  Gooch  filter,  then  washing  with  another  20  Cc.  of  water, 
the  volume  being  adjusted  finally  to  90  Cc.  and  the  determination 
completed  as  before.  Since  the  difference  is  one  third,  it  is  useful 
to  remember  that  by  multiplying  the  number  of  Cc.  of  standard  so- 
lution used  to  effect  the  match  by  0.3  (since  1  Cc.  =  1/10  Mgm.) 
one  gets  the  milligrams  of  free  acid  in  the  tablets  taken.  For  ex- 
ample :  two  tablets  were  treated  as  described,  and  required  3  Cc.  of 
