ON  THE  PREPARATION  OP  CHLOROFORM.  425 
and  153^.  Heated  above  167^,  the  yield  decreases  as  in 
Group  III.,  and  the  chloroform  contains  more  chlorine.  At  and 
below  122^,  the  yield  likewise  decreases,  (Exps.  11  and  12,) 
but  the  chloroform  is  entirely  free  from  chlorine  or  its  acids,  if 
a  sufficient  time  has  elapsed  before  artificial  heat  was  applied. 
The  most  variable  quantity  of  chloroform  is  afforded  if  the 
ingredients  are  mixed  at  ordinary  temperature,  and  the  formation 
induced  by  heating  afterwards.  If  the  mixture  is  heated  rapidly, 
and  the  temperature  passes  quickly  above  167°,  the  amount  of 
chloroform  decreases;  it  contains  much  chlorine  and  evolves  heat 
spontaneously;  moreover,  the  mass  is  apt  to  pass  over,  and 
many  troublesome  precautionary  measures  are  requisite  to  retain 
it  in  the  still.  If,  on  the  other  hand,  the  fire  is  removed  after 
the  temperature  of  between  135  and  167^  is  attained,  the  yield 
will  be  favorable.  This  circumstance  explains  the  increased 
amount  with  a  larger  quantity  of  water  in  proportion  to  the 
chlorinated  lime,  as  then  the  proper  temperature  may  be  acci- 
dentally more  easily  reached ;  but  with  the  greatest  care  the 
yield  is  very  variable. 
By  operating  as  directed  for  Group  II.  of  the  experiments, 
the  chloroform  distils  spontaneously  without  danger  for  the  mass 
to  pass  over,  though  the  still  may  be  far  more  than  half  filled. 
After  the  cessation  of  the  distillation,  the  supernatant  portion 
is  returned  and  with  a  slight  heat  rectified ;  or  it  might  perhaps 
be  better  to  distil  it  by  itself  from  a  glass  retort,  or  preserve  it 
for  the  next  operation. 
Much  of  the  result  depends  likewise  on  the  shape  and  other 
conditions  of  the  still.  If  made  of  a  good  conductor  of  heat,  or 
being  exposed  to  draughts  of  air,  or  supplied  with  a  high  head, 
the  still  will  be  refrigerated,  and  the  contents  require  to  be 
heated  previously  a  few  degrees  higher,  or  the  application  of 
heat  after  the  temperature  has  begun  to  fall.  Larger  quantities  of 
material  will  of  course  less  readily  be  cooled  down. 
The  author  used  likewise  three  other  vessels  for  preparing 
chloroform,  from  three  to  ten  pounds  of  chlorinated  lime.  Em- 
ploying a  common  demijohn  set  in  straw,  and  cooling  with  a 
Liebig's  condenser,  he  obtained  from  ten  pounds  of  chlorinated 
lime  6  per  cent,  chloroform.  A  cask  appears  to  be  the  most 
suitable  still  for  chloroform,  if  connected  with  a  good  refrige- 
