438    MANUFACTURE,  IMPURITIES  AND  TESTS  OF  CHLOROFORM. 
The  slow  decomposition  before  alluded  to  as  liable  to  occur  in 
chloroform  of  high  density,  is  easily  detected,  first,  by  the  odor 
of  chlorine,  which  is  more  strongly  marked  on  first  opening  the 
bottle, — and  again,  by  suspending  moistened  blue  litmus  paper 
in  the  bottle  above  the  liquid.  This  decomposition  commences, 
and  in  most  cases  is  limited  to  the  vapor  above  the  liquid.  When 
it  has  seriously  affected  the  liquid  chloroform,  there  is  little 
danger  but  that  the  specimen  will  be  rejected,  for  the  odor  of 
chlorine  is  then  so  strong  and  pungent  that  it  becomes  almost 
impossible  to  inhale  the  vapor.  Chloroform  that  is  undergoing 
the  slow  decomposition  from  too  high  density  alone,  may  give  no 
acid  or  bleaching  reaction  with  litmus  paper,  when  immersed  in 
the  liquid,  nor  more  than  the  faintest  possible  cloudiness  when 
shaken  with  solution  of  nitrate  of  silver,  but  if  a  piece  of  moistened 
litmus  paper  be  suspended  in  the  vapor  within  the  bottle,  it 
first  becomes  of  a  reddish  tinge,  about  the  edges  first,  and  is  then 
more  or  less  bleached,  or  turned  of  a  dingy  white  color.  Test 
paper  so  suspended  becomes  more  or  less  red  within  half  an  hour, 
in  almost  all  samples  of  good  chloroform  that  has  been  long 
kept,  but  is  never  bleached  unless  decomposition  is  going  on. 
This  distinction  of  reaction  is  important,  and'  affords  very  clear 
indications.  In  ordinary  commercial  chloroform  of  low  density, 
the  vapor  above  the  liquid  is  rarely  acid,  even  when  the  liquid 
itself  is  so.  When  very  delicate  shades  of  acid  reaction  are  to 
be  detected,  the  strip  of  blue  litmus  paper  should  be  torn  rather 
than  cut  at  its  free  extremity,  and  the  reaction  looked  for  upon 
the  projecting  fibres  of  the  torn  edges. 
It  has  been  before  stated  that  the  addition  of  a  small  portion 
of  alcohol  prevents  the  decomposition  of  good  chloroform.  The 
addition  of  alcohol  also  arrests  this  decomposition,  even  after  it 
has  gone  on  for  many  weeks,  but  it  does  not  of  course  free  the 
remaining  chloroform  from  the  products  of  the  decomposition. 
In  this  case  a  new  rectification  is  required  to  separate  the  watery 
looking  fluid  which  is  produced,  and  either  adheres  to  the  bottle 
about  the  edges  of  the  surface  of  the  chloroform,  or  is  diffused 
through  it,  rendering  it  opalescent.  The  appearance  of  this 
liquid  on  the  addition  of  alcohol  is  an  unfailing  test  of  the  con- 
dition of  the  chloroform  in  this  respect.  New  rectification  from 
powdered  quick-lime  separates  this  fluid,  and  renovates  the  chlo- 
roform entirely. 
