1 84  The  U.S. P.  Melting  Points.         { AmApS"ri9ioarm" 
by  direct  application  of  a  small  Bnnsen  flame  to  the  walls  of  the 
container,  special  care  being  taken  in  all  cases  to  insure  a  definite 
uniform  rise  in  temperature  within  a  certain  range  of  the  melting 
point.  Further  details  of  manipulation  will  be  briefly  indicated  in 
my  discussion  of  the  remaining  causes  of  divergence. 
The  37  compounds  mentioned  above  are,  with  some  exceptions, 
included  only  in  that  class  of  pharmacopceial  compounds  whose 
melting  point  determination  by  a  capillary  tube  method  offers  no 
complication.  I  believe,  however,  that  the  application  of  this 
method  to  all  other  classes  (such  as  fats,  waxes,  etc.)  involves  only 
modification  in  details  and  procedure  and  not  any  material  change 
of  apparatus.  Furthermore,  I  can  see  no  objection  to  applying  it 
as  a  modification  of  Landolt's  method  in  those  cases  where  it  would 
seem  feasible  and  desirable  to  determine  the  melting  point  or  freez- 
ing point  of  a  compound  by  using  a  comparatively  large  amount, 
with  the  thermometer  dipping  directly  into  the  substance. 
As  an  official  method  doubtless  some  will  criticize  the  one  sug- 
gested as  being  too  crude  to  insure  the  degree  of  accuracy  and 
refinement  that  is  desired  in  a  standard  value.  But  it  seems  to 
me  that  the  principal  object  in  the  standardization  of  melting  points 
— at  least  from  the  present  view  of  the  Pharmacopoeia — is,  not  so 
much  to  adopt  a  method  which  will  insure  the  utmost  degree  of 
accuracy  and  refinement  attainable,  however  desirable  that  might 
be,  as  it  is  to  adopt  a  method  which  shall  'be  readily  available  to, 
and  easily  applied  by,  all  concerned  with  the  melting  points  of 
pharmacopceial  compounds,  and  which  shall  be  capable  of  reasonably 
concordant  results  as  obtained  by  different  manipulators,  which 
after  all  is  a  very  fair  test  of  accuracy. 
Though  intending  to  be  brief  I  have  doubtless  devoted  more 
time  to  my  discussion  of  methods  than  would  perhaps  seem  desir- 
able in  the  scope  of  a  short  paper  involving  other  phases,  but  in 
any  standardization  the  question  of  methods  is  the  fundamental 
and  probably  the  most  important  consideration — which  fact  may 
offer  some  justification  for  my  slight  elaboration  upon  this  point. 
My  indulgence,  however,  will  necessitate  a  very  brief  discussion  of 
the  remaining  causes  if  this  paper  is  not  to  unreasonably  encroach 
upon  the  other  features  of  your  programme. 
That  varying  manipulation  in  melting  point  work  may  result  in 
different  values  for  the  same  compound  has  been  experimentally 
demonstrated,  and  is  further  indicated  by  the  recommendations  of 
