Am.  Jour.  Pharm. ) 
April,  1910.  J 
The  US.P.  Melting  Points. 
183 
of  the  apparatus,  which*  consisted  in  fitting  the  container  with  a 
cork,  perforated  for  the  thermometer  and  for  the  stirrer  and  with 
two  or  three  small  vents  at  the  edge  to  avoid  excessive  pressure. 
With  this  modification,  a  very  pure  grade  of  cotton-seed  oil,  freshly 
distilled  paraffin,  certain  mineral  oils,  and  a  few  other  substances 
could  be  conveniently  used  up  to  3000  C.  or  over  ;  but  they  soon 
become  colored  and  have  to  be  frequently  renewed.  A  bath  was 
finally  adopted  consisting  of  a  mixture  of  pure  concentrated  sul- 
phuric acid  and  potassium  sulphate  in  definite  proportions  as 
recommended  by  Mulliken.1  In  my  experience  this  bath,  contrary 
to  the  claims  made  for  it,  fumes  at  high  temperature  almost  as  badly 
as  the  pure  sulphuric  acid.  With  the  simple  cork  modification  the 
fumes  would  char  the  cork  and  quickly  spoil  the  bath,  but  by 
attaching  a  disk  of  thin  asbestos  to  the  bottom  of  the  cork  and 
including  a  glass  tube  in  the  perforation  for  the  stirrer  both  the 
fuming  and  the  charring  were  effectively  overcome  and  the  bath 
could  be  used  as  high  as  350°  C,  or  even  to  3700  C,  with  perfect 
convenience  and  safety.  In  all  cases  -  where  the  cork  modification 
was  applied  the  stirrer,  in  order  to  avoid  inconvenience  in  attaching 
the  capillary  tube  to  the  thermometer,  was  made  in  two  parts,  the 
first  part  extending  through  and  about  one-half  inch  above  the  cork ; 
the  second  part  being  the  remainder  of  the  stirrer  as  first  described. 
The  two  parts  are  easily  joined,  with  ample  security,  by  means  of 
a  small  piece  of  small  bore  rubber  tubing.  The  advantage  of  such 
an  arrangement  in  connection  with  the  cork  hardly  needs  further 
discussion. 
The  dark  color  gradually  acquired  by  the  bath  from  contamina- 
tion with  organic  compounds  can  be  readily  cleared  from  time  to 
time  by  adding  a  pinch  of  potassium  nitrate  and  in  this  way  con- 
tinuous use  for  a  large  number  of  determinations  is  possible.  I 
have  myself  made  considerably  more  than  100  determinations  with- 
out renewing  the  bath. 
This  method  has  been  applied  to  the  suggested  standardization 
of  the  melting  points  of  about  37  of  the  more  important  pharma- 
copceial  compounds,  involving  from  4  to  8  or  more  determinations 
on  each  of  5  to  8  samples  of  the  individual  compounds  (with  a  few 
exceptions).    In  making  these  determinations  the  bath  was  heated 
1  S.  P.  Mulliken :  "  Identification  of  Pure  Organic  Compounds,"  vol.  i, 
p.  219. 
