ON  CHLOROFORM. 
303 
by  a  careful  distillation,  leaving  about  one  or  two  per  cent,  in 
the  retort,  which  will  almost  always  react  very  decidedly  with 
concentrated  sulphuric  acid.  This  is  due  to  the  difficulty  of  de- 
stroying these  compounds  by  sulphuric  acid  in  operations  on  the 
large  scale,  which  is  completely  effected  only  by  very  prolonged 
contact,  and  then  probably — at  least  the  last  portions — with 
difficulty.  If  chloroform  treated  in  this  way  is  afterwards  care- 
fully rectified,  the  last  portions  of  the  distillate  will  usually  react 
with  sulphuric  acid. 
A  re-rectification  is  easily  accomplished,  and  without  much 
trouble.  The  chloroform  is  introduced  into  a  glass  retort  to- 
gether with  a  wire  coil,  a  thermometer  is  inserted,  and  the  retort 
placed  in  a  water-bath,  which  is  rapidly  heated  until  the  chloro- 
form boils,  when  the  heat  is  sufficiently  reduced  so  as  to  keep 
the  temperature  at  about  the  same  point,  taking  care  not  to  let 
it  rise  above  67°  C.  (153°  F.)  The  boiling  point  of  chloroform 
varies  with  its  density,  and  from  accidental  causes.  Liebig 
states  that  chloroform  of  1*480  sp.  gr.  boils  in  a  dry  retort  at 
60-8°  C.  (141-5°  F.),  but  in  the  presence  of  water  at  57-3°  C. 
(135*14°  F.)  If  the  temperature  is  in  no  case  allowed  to  rise 
over  67°  C.  (153°  F.),  the  last  portions  of  the  foreign  impurities 
are  left  behind,  which,  if  present  in  minute  proportion,  may  not 
be  positively  injurious,  but  which  possess  such  a  suffocating  odor 
that  their  complete  removal  is  at  _  least  very  desirable.  The 
temperature  suggested  here  is  a  few  degrees  less  thau  that  re- 
commended by  Hirsch,  but  is  sufficiently  high  for  the  distillation 
of  pure  chloroform. 
For  some  time  past  I  have,  for  reasons  stated  before,  reduced 
the  chloroform  to  the  specific  gravity  1*475.  If  95  per  cent, 
alcohol,  in  sufficient  quantity  for  this  purpose,  is  added  to  chloro- 
form of  a  higher  density,  the  mixture  turns  milky  ;  and  if  it  is 
now  subjected  to  distillation  even  in  the  presence  of  dry  carbon- 
ate of  potassa,  as  directed  by  the  pharmacopoeia,  a  considerable 
and  varying  proportion  distils  over  at  first  in  a  milky  condition, 
and  contains  all  the  water,  notwithstanding  this  liquid  boils  at 
about  33°  C.  (60°  F.)  above  the  boiling  point  of  chloroform. 
The  milkiness  of  the  mixture  is  caused  by  the  separation  of 
water  in  minute  globules ;  and,  if  it  is  allowed  to  rest,  this  water 
