^^'£y^'im!"^'}  German  Pharmacopoeia  Requirements.  227 
It  seems  to  me  also  that  in  the  matter  of  definition  of  the  melting 
point  the  book  leaves  a  large  opening  for  progress  toward  more 
rational  and  adequate  pharmacopoeial  standardization.  I  am  firmly 
of  the  opinion  that  the  requirement  of  a  definite  melting  interval 
or  range  rather  than  a  melting  point,  would  establish  a  more 
logical  and  effective  standard. 
The  old  requirements  for  the  fats  and  fatty  substances  involve 
the  use  of  a  thin-walled  capillary  tube  of  not  more  than  i  mm. 
diameter,  open  at  both  ends.  Enough  of  the  melted  fat  is  drawn 
into  one  end  of  the  tube  to  form  a  column  about  i  cm.  high,  and 
is  then  cooled  at  10°  for  24  hours  to  insure  complete  solidification. 
Attached  to  suitable  thermometer  the  sample  is  immersed  in  water 
contained  in  a  test  tube  of  30  mm.  diameter.  The  bath  is  gradually 
warmed  with  frequent  stirring.  The  temperature  at  which  the  fat 
becomes  transparent  and  rises  in  the  tube  is  the  melting  point. 
The  new  requirements  differ  in  the  following  details: 
1.  A  U-shaped  capillary  of  0.5-1  mm.  diameter,  filled  with 
molten  fat  to  the  same  level  in  each  arm  replaces  the  straight  tube. 
2.  The  sample  is  cooled  on  ice  for  2  hours,  or  at  10°  for  24 
hours. 
3.  The  charged  tube  is  attached  to  a  suitable  thermometer  so 
that  the  sample  will  be  on  a  level  with  the  thermometer  bulb. 
4.  A  bath  of  equal  parts  of  glycerin  and  water  displaces  the 
bath  of  sulphuric  acid. 
5.  Temperature  must  be  raised  "  very  slowly  "  to  avoid  super- 
heating. 
6.  That  temperature  at  whjch  the  fat  becomes  perfectly  clear 
and  transparent  is  the  melting  point. 
I  am  of  the  tentative  opinion  that  the  U-capillary  is  not  an 
improvement  over  the  straight  capillary  in  determining  the  melting 
point  of  fats.  This  constant  is  generally  more  difficult  of  exact 
determination  as  applied  to  fats  than  for  the  other  class  of  com- 
pounds. It  is  claimed  by  authorities  on  fats  that  some  fats  become 
clear  and  transparent  before  complete  melting  while  others  remain 
cloudy  for  some  time  after,  and  therefore  perfect  clearness  and 
transparency  is  not  a  good  criterion  of  the  melting  point.  For 
the  purpose  of  pharmacopoeial  standardization,  however,  the  main 
thing,  it  seems  to  me,  is  to  select  some  behavior,  in  the  region  of 
the  much  mooted  "  true  melting  point/'  which  is  easily  observed 
and  reasonably  constant.    With  the  old  method,  the  rise  of  the 
