1 82 
The  US.P.  Melting  Points. 
j  Am.  Jour.  Eharm. 
\      April,  1910. 
serious  cause  of  discordant  results  in  melting  point  determinations. 
In  so  far  as  this  cause  accounts  for  divergence  in  U.  S.  pharma- 
ceutical practice,  the  remedy  is  obviously  the  adoption  by  the  U.S. P. 
Committee  on  Revision  of  a  carefully  defined  official  method. 
In  an  attempt  recently  made  in  the  Hygienic  Laboratory  to 
select  or  devise  a  method  which  could  be  recommended  for  such  a 
purpose  it  was  not  considered  feasible  to  experimentally  test  a 
great  variety  of  methods,  nor  indeed  was  such  a  time  consuming 
procedure  necessary,  for  the  specifications  laid  before  us  by  the 
Committee  on  Revision,  calling  for  the  utmost  simplicity,  avail- 
ability, and  economy  consistent  with  reasonable  efficiency,  made  pos- 
sible the  elimination  by  inspection  of  practically  all  methods  except 
one  or  two  which  we  considered  to  offer  promise.  Comparative 
experimental  tests  were  made  upon  two  methods  but  the  conclusion 
was  soon  reached  that  the  simpler — applied  with  carefully  defined 
procedure — would  probably  easily  meet  all  practical  requirement^ 
of  pharmaceutical  practice  and,  at  the  same  time,  very  greatly 
improve  the  present  standard.  This  method  consists  of  one  of  the 
capillary-tube  variety,  more  or  less  modified  to  meet  specific  con- 
ditions as  they  developed.  It  involves  the  use  of  a  simple  round- 
bottom  straight  glass  tube  of  about  30  mm.  internal  diameter  and 
about  100  mm.  long,  flaring  slightly  at  the  top  like  an  ordinary  test- 
tube.  This  tube  or  container  is  fitted  with  a  stirring  device,  which 
any  one  can  make  in  a  few  minutes  from  a  piece  of  small  sized, 
thick-walled  capillary  glass  tubing  of  such  length  that  a  double 
bend  above  the  top  of  the  container  brings  the  outer  end  of  the 
stirrer  within  easy  reaching  distance  of  the  hand  for  convenience 
in  manipulation.  When  in  use  the  container  is  filled  with  a  suitable 
bath  to  a  depth  which  will  permit  of  such  an  immersion  of  the  bulb 
of  the  thermometer  that  the  upper  end  of  the  bulb  will  be  2  to  3  cm. 
below  the  surface  of  the  bath  and  the  lower  end  of  the  bulb  about 
equally  distant  from  the  bottom  of  the  container. 
For  melting  points  up  to  1500  C. — or  even  to  1800  C. — pure 
concentrated  sulphuric  acid  was  considered  the  most  suitable  and 
satisfactory  bath.  When  fresh  it  can  be  used  at  much  higher  tem- 
perature but  then  its  very  irritating  fumes  make  it  decidedly  objec- 
tionable. After  much  experimentation  no  bath  could  be  found  suit- 
able for  work  at  temperatures  much  above  2000  C.  which  was  not 
more  or  less  objectionable  because  of  fuming.  This  difficulty,  how- 
ever, was  found  to  be  effectively  overcome  by  a  slight  modification 
