228  German  Pharmacopoeia  Requirements.  {'^"'  Viariyii**'"' 
fat  in  the  tube  under  the  sHght  pressure  of  the  water  would  seem 
to  fulfill  such  a  condition  and  to  indicate  at  least  the  melting  point 
of  that  portion  of  the  fat  which  is  in  direct  contact  with  the  tube. 
More  extended  experience  with  fats  might  of  course  change  my 
views  on  this  point. 
The  absence  of  stirring  as  a  requirement  in  these  determinations, 
although  perhaps  not  so  serious  an  omission  as  for  melting  points 
at  higher  temperature,  still  seems  to  me  a  mistake. 
The  requirement  in  the  new  edition  of  a  method  for  the  determina- 
tion of  freezing  points  is  all  on  the  credit  side — no  such  requirement 
being  found  in  the  old  edition.  The  method  is  substantially  as 
follows:  Ten  grams  of  the  substance  under  investigation  are  care- 
fully melted  in  a  test  tube  containing  a  suitable  thermometer.  By 
dipping  the  tube  in  water,  the  temperature  of  which  is  about  5° 
C.  below  the  freezing  point  of  the  substance,  the  melt  is  cooled 
to  about  2°  below  the  freezing  point;  then  by  stirring  with  the 
thermometer,  or  if  necessary  by  seeding  with  a  small  crystal  of  the 
substance  under  investigation,  freezing  is  induced  and  the  highest 
temperature  observed  during  the  freezing  process  is  the  freezing 
point. 
The  method  has  the  advantage  of  extreme  simplicity,  and  is 
therefore  readily  available  to  all  concerned.  It  is  also  probably 
adequate  for  the  purpose  intended,  but  without  personal  experience 
with  the  method  I  hesitate  to  offer  critical  comment,  except  per- 
haps that  the  dimensions  of  the  test  tube,  and  also  of  the  ther- 
mometer, used  should  be  specified.  The  latter  criticism  is  oi 
general  application  and  will  be  referred  to  later. 
Just  as  for  the  freezing  point,  the  methods  described  for  the 
determination  of  the  boiling  point  constitute  a  feature  of  the  new 
edition  not  found  in  the  old,  and  therefore  represent  a  distinct 
advance  in  standardization. 
As  in  the  case  of  the  melting  point,  the  boiling  point  require- 
ments are  divided  into  2  parts : 
The  first  part  describes  a  method  which  is  intended  to  serve 
only  as  a  means  of  identification  of  the  liquid,  and  not  as  a  test 
of  its  purity.  The  procedure  is  somewhat  similar  to  that  described 
for  the  first  melting  point  method.  A  thin-walled  capillary  tube 
of  3  mm.  internal  diameter  and  containing  1-2  drops  of  the  liquid 
under  investigation  is  attached  to  a  suitable  thermometer  and  im- 
mersed in  a  bath  of  sulphuric  acid  just  as  in  the  first  melting- 
