"^""'May ^911*^™' I  German  Pharmacopoeia  Requirements,  229 
point  method.  A  second  capillary  tube  open  at  the  lower  end  and 
sealed  about  2  mm.  above  the  open  end  dips  into  the  liquid  in  the 
main  capillary  to  prevent  bumping.  The  temperature  at  which 
an  unbroken  series  of  bubbles  begins  to  rise  from  the  bottom  of  the 
liquid  is  the  boiling  point. 
Having  had  no  experience  with  this  or  a  similar  method  I 
offer  no  critical  comment. 
The  second  boiling  point  method  described  is  intended  to  deter- 
mine the  purity  of  the  liquid  and  of  course  involves  distillation. 
It  is  required  that  at  least  50  c.c.  of  the  substance  be  distilled 
from  a  distilling  flask  of  75-80  c.c.  capacity.  The  bulb  of  the 
thermometer  must  be  placed  i  cm.  below  the  delivery  tube  of  the 
flask.  Before  beginning  distillation  a  small  piece  of  broken  porce- 
lain is  placed  in  the  liquid  tO'  prevent  bumping.  The  flask  is  heated 
in  an  air  bath.  Nearly  the  entire  liquid  must  distill  over  within 
the  required  temperature — any  low  boiling  fraction  and  any  residue 
should  be  only  very  small. 
It  seems  to  me  that  this  method  might  be  improved  by  being 
more  specific  in  detail ;  for  instance,  the  length  and  diameter  of  the 
neck  of  the  flask  and  the  position  of  the  delivery  tube  with  relation 
to  the  mouth  of  the  flask  should  be  defined.  Also  such  indefinite 
phraseology  as  nearly  "  and  very  small "  are  surely  out  of  place 
in  the  standardization  of  a  physical  constant.  It  would  seem 
feasible,  instead,  to  incorporate  in  the  description  of  individual 
liquids  a  percentage  yield  of  distillate  that  should  be  obtained  within 
the  required  limits  of  temperature ;  or  to  have  a  general  percentage- 
yield  requirement,  applied  to  all  liquids    unless  otherwise  stated." 
Finally:  I  consider  that  the  general  requirements  covering 
melting  points,  freezing  points  and  boiling  points,  are  seri- 
ously deficient  in  the  lack  of  more  specific  limitations  re- 
garding the  thermometer  to  be  used.  The  book  uniformly  pre- 
scribes the  use  of  einem'  geeigneten  Thermometer  " — a  phrase, 
which  I  have  translated  "  a  suitable  thermometer/'  although  pos- 
sibly it  could  with  equal  accuracy  be  interpreted  to  mean  "  an 
accurate  thermometer."  In  either  case,  however,  my  criticism 
applies,  with  little  variation.  Much  argument  might  be  ofifered  to 
justify  my  attitude  on  this  point — a  single  illustration  I  believe 
will  serve  the  purpose :  Of  two  equally  accurate  thermometers, 
standardized  in  the  same  way  and  covering  the  same  range,  one 
might  be  six  inches  long  and  the  other  three  feet  long — obviously 
