^jjiy/'xgjg™*}      American  Acetylsalicylic  Acid.  523 
the  U.  S.  Pharmacopoeia  modified  by  first  heating  the  bath  to  1200 
C.  before  attaching  the  melting-point  tube  to  the  thermometer. 
The  melting  point  of  purified  acetylsalicylic  acid  was  found  to 
be  131. 5-132. 50  C.  (corr.).7  With  the  exception  of  one  specimen, 
which  was  obviously  impure,  the  various  specimens  examined  melted 
between  1280  and  1330  C.  as  may  be  seen  in  the  accompanying  table. 
It  would  appear  that  this  range  of  melting  points  would  be  more 
acceptable  and  reliable  than  the  melting  points  described  in  various 
standards. 
Presence  or  Absence  of  Free  Salicylic  Acid. — It  is  generally 
conceded  that  the  presence  of  salicylic  acid  in  amounts  more  than 
traces  is  deleterious.  Furthermore,  the  mount  of  salicylic  acid  is 
a  good  index  of  the  purity  of  the  acetylsalicyclic  acid,  because  the 
test  is  so  delicate  that,  under  favorable  conditions,  mere  traces  may 
be  determined  and,  as  a  rule,  the  better  the  product,  the  less  the 
amount  of  free  salicylic  acid. 
The  tests  appearing  in  various  pharmacopoeias  for  salicylic  acid 
as  an  impurity  in  acetylsalicylic  acid  do  not  give  concordant  results, 
different  workers  interpreting  the  results  differently,  nor  are  they 
detailed  in  such  a  manner  as  to  yield  maximum  delicacy. 
After  experimentation,  it  was  decided  to  establish  a  "  limit "  test 
of  approximately  0.1  per  cent,  free  salicylic  acid,  when  carried  out 
according  to  the  following  method: 
0.1  G.  of  the  substance  was  placed  in  a  dry  colorimeter  tube  and  1  Cc. 
of  alcohol,8  previously  distilled  over  NaOH,  was  added.  After  the  acetyl- 
salicylic acid  had  dissolved,  48  Cc.  of  water  and  1  Cc.  of  fresh  0.1  per  cent, 
ferric  chloride  (FeCls-6H20)  solution  were  added.  At  the  same  time  a  con- 
trol was  run  by  treating  1  Cc.  of  a  "  standard  "  salicylate  solution  the  same 
as  above.9  If  within  two  minutes  the  color  given  by  the  acetylsalicylic  acid 
is  not  more  intense  than  the  color  given 'by  the  "standard,"  the  presence  of 
not  more  than  0.1  per  cent,  free  salicylic  acid10  is  proved. 
7  Isolated  crystals  attached  to  the  walls  of  the  melting-point  tube,  apart 
from  the  bulk  of  acetylsalicylic  acid,  melted  at  a  lower  temperature. 
8  An  excess  of  alcohol  destroys  or  lessens  the  color  when  only  a  very 
minute  amount  of  salicylic  acid  is  present. 
9  The  control  should  be  made  each  time  as  standing  in  the  air  changes 
its  tinctorial  power. 
10  The  presence  of  pure  acetylsalicylic  acid  does  not  seem  to  affect  the 
iron  (Fe+  +  +)  salicylic  acid  coloration.  The  small  amount  of  acetic  acid 
was  added  to  the  sodium  salicylate  control  solution  (1)  to  simulate  an 
acidity  approximating  the  acidity  of  the  acetylsalicylic  acid,  and  (2)  since 
