Am.  Jour.  Pharm. ) 
September,  1906.  J 
Criticisms  of  the  U.S. P. 
415 
official  method,  with  very  much  less  chance  of  error,  and  it  requires 
only  about  a  half-hour  for  the  entire  determination.  (Charles  E. 
Caspari,  in  Meyer  Bros1.  Drug.,  1905,  page  249.) 
DIRECTIONS  FOR  DETERMINING  MELTING-POINT  ARE  MISSED. 
Among  the  things  not  found  in  the  U.S.P.  are  directions  for  deter- 
mining the  melting-point  of  various  substances.  This  determination 
of  the  melting-point  is,  in  the  majority  of  cases,  such  a  satisfactory 
evidence  of  the  identity  and  purity  of  a  chemical  that  all  other  tests 
may  frequently  be  omitted. 
The  German  Pharmacopoeia  devotes  considerable  amount  of  space 
to  a  description  of  how  the  melting-point  is  to  be  determined,  and 
further  defines  the  melting-point  as  that  degree  of  heat  at  which  the 
opaque  substance  melts  down  to  transparent  drops.  (Otto  Herting, 
in  D.  A.  Apoth.  Zeitg.y  1905,  page  71.) 
MELTING-POINT  FOR  STEARIC  ACID  SHOULD  BE  HIGHER. 
The  commercial  stearic  acid  is  practically  the  only  kind  that  is  of 
interest  to  the  pharmacist,  and  the  Pharmacopoeia  specifies  a  melt- 
ing-point of  not  lower  than  560  C.  According  to  Brannt  ("Animal 
and  Vegetable  Fats  and  Oils,"  Vol.  I,  page  148)  this  melting-point 
corresponds  to  a  mixture  of  60  per  cent,  palmitic  acid  and  40  per 
cent,  stearic  acid,  the  former  being,  from  the  source  and  process  of 
manufacture,  the  substance  that  is  naturally  present  in  addition  to 
the  stearic  acid.  A  very  large  proportion  of  the  commercial  article 
has  a  lower  melting-point  than  560  C,  and  it  should  be  remembered 
that  a  difference  of  2°  or  30  produces  a  marked  effect  upon  the 
consistence  of  glycerin  suppositories;  where  an  acid  of  540  C. 
melting-pointing  is  used,  the  resulting  base  is  too  soft,  and  does  not 
hold  glycerin  well  at  ordinary  temperatures.  It  will  repay  the 
slightly  increased  cost  to  specify  "  stearic  acid  extra,"  having  a 
melting-point  of  580  C.  (Dr.  J.  M.  Francis,  in  Bull,  of  Phar.,  1905, 
Page  317.) 
