522  American  Acetylsalicylic  Acid.  {Am'J^r-IJIh8arm' 
Melting  Poixt. — The  melting  point  of  acetylsalicylic  acid  has 
been  given  at  various  temperatures  from  n8°  to  1370  C.  ;3  the  British 
Pharmacopoeia  describes  the  melting  point  at  1330  to  1 35 0  C. ;  the 
German  Pharmacopoeia" 'about  135 0  C";  the  French  Pharmacopoeia 
at  1 35 0  C. ;  New  and  Nonofficial  Remedies,  1917,  I34-I36°C.  The 
Bayer  Company,  in  the  patent  trial  at  Qhicago  a  number  of  years 
ago,  gave  among  the  "four  infallible  tests"  a  melting  point  of  "about 
I35°  C."  Several  men  have  carefully  determined  the  melting  point 
in  recent  years.  Emery  and  Wright4  in  1912  found  that  "Aspirin, 
Bayer  ''  melted  at  130.5-1310  C.  In  France,  Francois5  has  deter- 
mined the  melting  point  of  pure  acetylsalicylic  acid,  which,  accord- 
ing to  his  method,  is  1320  C.  When  various  samples  of  acetylsali- 
cylic acid  were  examined  in  this  laboratory,  it  was  found  that  the 
melting  point  of  none  was  as  high  as  that  described  in  New  and 
Nonofficial  Remedies  or  the  British,  French,  or  German  pharma- 
copoeias when  taken  according  to  the  general  method  of  the  U.  S. 
Pharmacopoeia,  vol.  9,  p.  596.  On  critical  observation,  it  may  be 
seen  that  the  melting  point  of  acetylsalicylic  acid  is  preceded  and 
accompanied  by  decomposition.  If  the  sample  in  the  melting  tube, 
is  heated  from  the  original  room  temperature  of  the  bath  to  1200 
C,  the  temperature  of  melting  will  be  lower  than  if  the  bath  is  first 
heated  to  1200  C.  and  the  melting-point  tube  then  placed  in  the 
bath.6  Thus  the  melting  point  of  acetylsalicylic  acid,  like  so  many 
organic  compounds  which  decompose  and  do  not  melt  sharply,  is 
unsatisfactory  and  cannot  be  taken  as  an  "  infallible  test "  of  purity, 
especially  when  determined  by  different  operators  who  do  not  give 
their  method  in  detail.  After  making  a  large  number  of  melting- 
point  determinations  of  acetylsalicylic  acid,  alone  and  in  parallel 
with  other  operators,  it  was  decided  to  use  the  method  described  in 
3  For  reference  to  older  literature  see  Beilstein,  II,  1496  (889). 
4  '*  The  Melting  Temperature  of  Aspirin  and  Salicylic  Acid  Mixtures," 
Proc.  Assoc.  Off.  Agr.  Chcm..  1912;  Bureau  of  Chemistry.  Department  of 
Agriculture,  Bull.  162. 
5  "  Assay  of  Aspirin."'  /.  pharm.  Cli'un.,  15  (1917).  No.  7.  213. 
6  Similar  observations  were  made  by  Emery  and  Wright,  who  state :  "  An 
accurate  determination  of  the  melting  temperature  in  this  way  (the  rate  of 
heating  was  such  as  to  give  a  rise  in  temperature  of  about  i°  per  minute)  is 
rendered  difficult  by  the  fact  that  '  aspirin  '  decomposes  on  heating,  as  evi- 
denced in  the  depression  of  the  melting  temperature  of  the  pure  substance  of 
about  ic  for  every  rive  minutes'  heating  just  below  its  melting  temperature." 
